THIf DOOK1J A PART
OF THE LIDRAR.Y OF
From the collection of the
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library
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San Francisco, California
2006
EXPERIMENTAL COOKERY
BOOKS IN HOME ECONOMICS
HOUSEHOLD EQUIPMENT. Second Edition. By
Louise Jenison Feet and Lenore E. Sater.
A FUNCTIONING PROGRAM or HOME ECONOMICS.
By Ivol Spa/ord.
A GUIDE TO TEXTILES. By Mary Evans and Ellen
Beers McGowan.
ADULT EDUCATION IN HOMEMAKING. By L. Belle
Pollard.
THE CONSUMER-BUYER AND THE MARKET. By
Jessie V. Coles.
FOOD SERVICE IN INSTITUTIONS. By Bessie Brooks
West and LeVelle Wood.
FUNDAMENTALS OF TEXTILES, A WORKBOOK. By
Eda A . Jacobsen and Helen E. McCullough.
FOOD FOR FIFTY. By Sina Faye Fowler and Bessie
Brooks West.
FUNDAMENTALS IN TEACHING HOME ECONOMICS.
By Ivol Spa/ord.
HOME FURNISHING. By Anna H. Rutt.
ECONOMICS OF HOUSEHOLD PRODUCTION. By
Margaret G. Reid.
FOOD PREPARATION. Second Edition. By Marion
Deyoe Sweetman.
MANUAL FOR FOOD PREPARATION STUDY. By
Florence B. King.
EXPERIMENTAL COOKERY FROM THE CHEMICAL AND
PHYSICAL STANDPOINT. Second Edition. By
Belle Lowe.
FOOD PREPARATION STUDIES. Second Edition. By
the late Alice M. Child and Kathryn Bele Niles.
FOOD PREPARATION RECIPES. By the late Alice M.
Child and Kathryn Bele Niles.
EXPERIMENTAL
COOKERY
From the Chemical and Physical Standpoint
BY
BELLE LOWE
Professor , Foods and Nutrition
Iowa State College
WITH A LABORATORY OUTLINE
SECOND EDITION
NEW YORK
JOHN WILEY & SONS, INC.
LONDON: CHAPMAN & HALL, LIMITED
COPYRIGHT, 1932, 1937
BY BELLE LOWE
All Rights Reserved
This book or any part thereof must not
be reproduced in any form without
the written permission of the publisher.
Printed in the U. S. A. 3/41
THE HADDON CRAFTSMEN, INC.
CAMDEN, N. J.
TO
ELIZABETH MILLER KOCH
with
acknowledgment of kelpy
inspiration., and encouragement
CONTENTS
CHAPTER PAGE
I. THE RELATION OF COOKERY TO COLLOID CHEMISTRY .... 1
II. SUGAR COOKERY 31
III. FREEZING 83
IV. FRUITS AND VEGETABLES 103
V. JELLY 152
VI. GELATIN 178
VII. MEAT 194
VIII. EMULSIONS 266
IX. MILK AND CHEESE 293
X. EGG COOKERY 323
XL FLOUR AND BREAD 391
XII. BATTERS AND DOUGHS 447
XIII. FATS AND OILS . 542
INDEX . 585
INTRODUCTION
The principal function of this volume is to present our newer knowl-
edge of food preparation and cookery processes from a chemical and physi-
cal basis, particularly that of colloid chemistry. In doing this, many results
secured from experimental work along these lines at Iowa State College
have been included. A condensed arrangement of the data on cookery,
which are found in widely scattered sources, has been included also.
Many of the sciences serve as a foundation or basis for food prepara-
tion. Inorganic, organic, physical, and plant chemistry, as well as physics
and other sciences, are necessary for an adequate understanding of many
processes in food preparation. But the subject matter herein covered is
perhaps more closely related to physical chemistry and the branch of
physical chemistry known as colloid chemistry. In fact, so many of the
ingredients used in food preparation are colloidal in nature that food
preparation may be classed as one field of applied colloid chemistry. As
a phase of colloid chemistry it offers a vast field for exploration, for
although commercially prepared foods have been studied extensively the
problems in connection with their preparation are far from completed.
Work along other lines of cookery has hardly started. Some of the older
work on cookery needs to be repeated and explained in the light of newer
interpretations of science.
Because the majority of home economics students have had no oppor-
tunity to take even an elementary course in physical or colloid chemistry,
it becomes necessary to present a simple outline and explanation of col-
loid chemistry in its relation to food preparation. Since this is the founda-
tion material for this treatise it seems logical to present it first. But to
many persons this is the newest and perhaps the most difficult subject
matter in relation to food preparation. Therefore, it is probably better for
the student to commence with the chapters on sugar cookery, freezing, and
fruits and vegetables, referring only to the few paragraphs in Chapter I
needed to understand some of the factors of sugar cookery and freezing.
A fundamental understanding of sugar cookery and freezing preparation
processes is based largely upon the portion of physical chemistry dealing
with solutions, vapor pressure, the boiling point, and the freezing point.
This material is outlined in these chapters. But to present the material
on colloid chemistry in such a manner in every chapter would lead to
many repetitions and make the book unduly long. Hence this material is
summarized in Chapter I, although the author realized that it would prob-
ably be necessary to review or to present portions of this chapter in connec-
tion with subsequent ones.
x INTRODUCTION
Many contradictory observations are often made in cookery. This is
to be expected, particularly when the materials used are in a colloidal
state. Unless the constituents of food products are present in the same
amount, and, even if present in the same proportion, if the colloidal
particles are not the same size, if the previous treatment, including the
thermal and mechanical treatment and the time element, is not exactly
duplicated, then even an elementary knowledge of colloid chemistry leads
one to expect different results in finished products, because of variation
of these different factors. It is not possible to control all these factors. For
instance, the variation in ash content of flour, eggs, milk, meat, fruits, and
vegetables is nearly always beyond our control. But the necessity for a
detailed description of the technic and method followed in reporting
results is obvious. Detailed directions in writing the laboratory outline
are essential or the technics followed may vary so much that the results
are worthless for comparisons. It is of course understood that adequate
explanations cannot be offered for all cookery processes. In some instances
it is necessary to determine the results time after time and let the theory
fit the laboratory facts. In other cases the explanations offered will need
to be changed, modified, or replaced by data obtained from future investi-
gations.
In starting the laboratory work the author asks her students to assume
the attitude that every result obtained is right. If it is not as expected,
what are the reasons? For example, a burned, charred product results from
certain procedures. If, when students have used the same proportions, the
same ingredients, and tried to follow the same technic, the individual
results differ, what are the possible interpretations for the divergence? In
the same manner the reported results of other investigators are taken as
correct. If the students' laboratory results do not always agree with
reported results, interest comes in comparing methods used, the ingredients
used, their proportion, and the technic followed, to find explanations for
agreement or disagreement.
It is hoped that this volume will fill a need for a textbook for discus-
sion material for food-preparation courses in colleges and as a reference
work for teachers of secondary schools. It is also hoped that the reference
to and summary of articles in the literature will create an interest on
the part of the student to read and interpret them for herself.
Food-preparation study in colleges may include courses designated as
experimental cookery. The material in this book may be given in such
courses. The manual "Food Preparation Studies" by Child-Niles-Kolshorn
will also be an aid in these courses.
To some the term experimental cookery implies only a method of
presenting material. Such is not the use of the expression in this volume.
It is used to designate a certain field of subject matter relating to food
preparation. The laboratory outline included in this volume is arranged
to present this subject matter as far as possible.
INTRODUCTION xi
What constitutes or should constitute experimental-cookery courses
cannot be answered fully at the present time. They are of necessity rapidly
developing and changing. The author believes that eventually they will
have the same relation to food-preparation courses that those in animal
feeding have to nutrition courses.
The author takes this opportunity to acknowledge with appreciation
the comments of Dr. P. Mabel Nelson, Florence Busse Smith, Alma
Plagge, Viola M. Bell, and the other members of the Foods and Nutrition
staff of Iowa State College. The aid of Dr. Amy Le Vesconte for many
/>H determinations is also acknowledged.
To Dr. E. A. Benbrook and Margaret Sloss of the Veterinary Depart-
ment the author is indebted for aid in taking photo-micrographs.
For reading portions of the manuscript and for the suggestions they
have offered, the author is also indebted to Dr. E. I. Fulmer (the chapter
on the Relation of Cookery to Colloid Chemistry) ; to Prof. M. Mortensen
and Prof. C. E. Iverson (the chapter on Freezing) ; to Dr. R. M. Hixon
(the chapter on Fruits and Vegetables) ; to Dr. Paul E. Howe and Prof.
M. D. Helser (the chapter on Meat) ; to Prof. M. Mortensen, Dr. E.
W. Bird, and Dr. B. W. Hammer (the chapter on Milk) ; and to Ethan
E. Hoovler (the entire book).
To the many students in her "Experimental Foods" classes who through
their interest and enthusiasm have always been a stimulus to further work,
the author wishes to express her most grateful appreciation.
EXPERIMENTAL COOKERY
CHAPTER I
THE RELATION OF COOKERY TO COLLOID
CHEMISTRY
The early lines of food work cannot be expressed better than in the
words of Ostwald (1922). "Scientific study of the field still contents itself
with chapters on analysis and the recognition of adulterants, but chapters
dealing with the preparation of food are hardly started. Much as every one
would like to obtain better food for less money, study of such questions
is regarded as menial and best left to the cook. A scientific study of the
preparation of food is considered as only amusing even in scientific circles."
Later Ostwald remarks that the chapters that are missing in food prepa-
ration are the ones to which colloid chemistry may be applied.
Since so many phases of food preparation are based on colloid chemistry
it seems necessary to include in this book a chapter on its relation to cook-
ery. It is a short and brief outline. As such, it can be used as an intro-
duction or as a summary or for both introduction and summary of the
work on food preparation, although the subsequent chapters have been
written with the idea that at least portions of this chapter will be used
in connection with each of them.
Thomas Graham's contributions constitute the foundations of colloid
chemistry. His most important results were published between 1861 and
1864. But it is only since the publications of von Weimarn and of Ostwald
in 1906 and 1907 that rapid development has been made in colloid chem-
istry, and it is an even shorter time since the most extensive applications
of it have been made to food preparation. Graham used the terms
crystalloids and colloids to apply to definite materials. Crystalloids were
dialyzable through parchment membrane, whereas colloids were not dialyz-
able. The terms are now misleading, for we know that any crystalloid can,
by a definite treatment and the selection of the right medium, be brought
into the colloidal state. Many of the so-called colloids can be crystallized.
The term colloidal state indicates that the material is dispersed in another
substance, so that it is preferable to speak of colloidal systems rather than
colloids. Colloidal systems differ from molecular ones in the size of the
dispersed particles. This difference in size of the particles gives different
physical properties to the system.
Bancroft states that "adopting the very flexible definition that a phase
1
2 RELATION OF COOKERY TO COLLOID CHEMISTRY
is called colloidal when it is sufficiently finely divided, colloid chemistry
is the chemistry of bubbles, drops, grains, filaments, and films, because in
each of these cases at least one dimension of the phase is very small. This is
not a truly scientific classification because a bubble has a film round it,
and a film may be considered as made up of coalescing drops or grains."
A knowledge of colloid chemistry is necessary to have a real understanding
of processes and methods used in a large number of industries and occupa-
tions. Bancroft gives a list of 60 such occupations, which include: "cream,
butter, cheese, and casein products; cooking and washing."
Classification of Substances Based upon the Degree of Dispersion
in Solution
Solutions and suspensions. When a solid substance is added to a
liquid one of three types of mixtures may be formed. (1) A true solution,
which is a homogeneous mixture. (2) A colloidal solution, which appears
to be homogeneous. The dispersed particles have a size of 1 m/x to 0.1^ and
can be separated by a sufficiently fine filter. (3) A suspension in which
the dispersed particles are greater than 0.1,u. The dispersed particles can
be separated from the liquid by filtration or sedimentation. Gortner
states, "Inasmuch as fine suspensions possess, to a large degree, certain
characteristic properties of colloidal systems, there has been a general tend-
ency of recent years to raise the upper limit to 0.5/x," instead of O.I p.. It
should be understood that the above classification is an arbitrary one and
that in nature there are no abrupt transitions. There can be no definite
division made between true and colloidal solutions for the transition is
gradual. There are some colloidal solutions known in which the dispersed
particles are less than 1 m/x. There is also no line of demarcation between
colloidal solutions and suspensions.
In true solutions the dispersed phase consists of particles of molecular
or ionic size, whereas the colloidal solutions contain particles of larger size,
and the suspension contains particles large enough for mechanical separation.
The smaller the particles with a definite quantity of material the more
dispersed the substance; the larger the particles the less dispersed. A true
solution can be reproduced if the temperature, pressure, and concentration
are known, since the degree of dispersion is constant. But in colloidal solu-
tions it is necessary to know the degree of dispersion as well as the tem-
perature, pressure, and concentration to reproduce the system. The prop-
erties of solutions like gelatin also depend upon the method of preparation
and their previous history; the properties of a true solution are independent
of the method of preparation or their previous history. The systems whose
properties are dependent upon their previous history are said to show
hysteresis.
Colloidal systems are heterogeneous, so that it is necessary to distinguish
which is the dispersed phase and which is the dispersing medium. Some of
SOLUTIONS AND SUSPENSIONS
the terms used are dispersed phase and dispersing medium- discontinuous
phase and continuous phase ; internal phase and external phase ; and micelles
and intermicellar liquid. The usage of the last group appears to be in-
creasing at the present time.
TABLE 1
CHARACTERISTIC DIFFERENCES OF
True solutions
Colloidal solutions
Suspensions
In molecular subdivision
Particles are not visible
with ultra-microscope
Particles less than 1 m/*
Formation of gels is not
characteristic
Transparent
Particles pass through
parchment membranes
Intense kinetic movement
Systems show high os-
motic pressure
In colloidal subdivision
Refracted light of parti-
cles is visible with ultra-
microscope
Particles from lm/x to 0.1 ju
Formation of gels is
characteristic
Transparent
Particles or micelles pass
through high-grade filter
paper, but not parchment
Less kinetic movement,
more Brownian move-
ment
Systems show low os-
motic pressure
In mechanical subdivision
Particles visible with or-
dinary microscope or
naked eye
Particles greater than 0. 1 n
Formation of gels is not
characteristic
Generally opaque
Particles do not pass
through high-grade filter
paper
Little movement
Systems show no measur-
able osmotic pressure
Particles of colloidal size may be in a gaseous, liquid, or a solid state.
These micelles may be dispersed in solids, liquids, or gases; and if sys-
tems are classified according to the dispersed and dispersing medium there
may be a
solid in a solid, ruby glass;
liquid in a solid, opals ;
gas in a solid, pumice ;
solid in a liquid, gold sol ;
liquid in a liquid, lyophilic colloids;
gas in a liquid, whipped cream ;
solid in a gas, smoke;
liquid in a gas, fog.
4 RELATION OF COOKERY TO COLLOID CHEMISTRY
Sometimes the classification of colloidal systems is based on the dispersed
phase only, and this is designated as a solid, liquid, or a gas, according to
the material dispersed. Gortner adds emulsions to the above eight systems
to be considered in colloidal systems.
Dispersion of substances. It is possible to change particles from
molecular size to suspension particles and vice versa. Ostwald states that
"it may be accomplished either through the dispersion of nondispersed or
coarsely dispersed substances, or through the condensation of molecularly
dispersed systems. To these ends not only chemical but mechanical, elec-
trical and other kinds of energy may be used." Water passes from the molec-
ular through the colloidal and into the suspension state in freezing. Von
Weimarn states that all crystalline substances pass through a colloidal
zone in going into solution and in crystallizing from solution, for during
crystallization the size of the particles increases, passing from molecular,
through colloidal, to suspension dimensions. This emphasizes the fact that,
within each group or class of substances, there may be a wide variation
in the degree of dispersion. This dispersion, as in crystallization, may pass
through molecular, colloidal, and suspension zones, whereas with other
substances there may be wide degrees of dispersion of the substance
within one zone. The properties of the systems vary with the size and
degree of dispersion of their particles, which affect the results obtained in
cookery. The properties of colloidal particles approaching molecular dis-
persion are different from those of particles approaching the suspension
zone. One illustration will be mentioned. The gluten particles of flour
have colloidal dimensions. According to Gortner and Doherty, not all
gluten particles from different flours are the same size. The gluten particles
in pastry flour are more dispersed or of smaller size than those in bread
flour. This is one reason for the different results obtained in baked foods
when bread flour is used instead of pastry flour. The properties and bak-
ing qualities of different flours vary with the size of the gluten particles.
Particles approaching the limits of the size of one zone may show prop-
erties of two zones. Thus sugar has a high molecular weight and in cookery
shows both molecular and colloidal properties as if it belonged to an in-
between group. In gelatin dishes with a definite concentration it increases
the stiffness of the gel ; in custards it acts like a protective colloid.
Increasing and Lessening the Degree of Dispersion of
Substances in Food Preparation
In food preparation many of the methods used and many of the in-
gredients added to foods bring about increased or decreased dispersion.
Heat. Increasing the temperature may bring about a greater or a lesser
degree of dispersion. The heating of water increases its dispersion. The dis-
persion of fat globules in milk is increased by the application of heat to
DISPERSION BY ALKALIES 5
the milk, but when proteins are coagulated by heat the degree of dispersion
is decreased.
Mechanical dispersion. Beating of a food is a mechanical means of
bringing about a greater or a lesser degree of dispersion. In cookery, stir-
ring may bring about more uniform distribution of particles in a food,
like white sauce. But even this may prevent lumping or clumping and thus
is a means of bringing about dispersion, just as beating a curdled custard
is a mechanical means of bringing about a greater degree of dispersion of
a suspension, but although it reduces the size of the curds it does not reduce
them enough to change the suspension to the colloidal state. Homogenization
of milk or cream is a mechanical means of increasing the dispersion of fat
particles. Beating an egg white is a mechanical means of lessening the
degree of dispersion, as it brings about partial coagulation of the egg white
in the cell walls surrounding the air bubbles.
Dispersion by acids. The addition or the development of acid in
preparation of food may be a chemical means of bringing about a greater or
a lesser degree of dispersion. For instance, the development of acid during
the fermentation of bread brings about greater dispersion of the gluten.
The addition of acid to whole egg tends to curdle the egg or bring about a
lessened degree of dispersion. If a large enough quantity of acid is added,
the degree of dispersion may be increased after passing through a zone
of lesser dispersion. The explanation of the different effects of acid on the
gluten and on the egg proteins depends upon the isoelectric point of the
gluten and the egg protein and the degree of acidity developed. This will
be considered later.
Dispersion by alkalies. The addition of alkalies may also tend to
bring about a greater or a lesser degree of dispersion. In quick breads and
cakes the addition of soda in excess of the amount required to neutralize
the acidity of the mixture may bring about increased dispersion of the
gluten particles, which results in a definite grain or crumb.
The different methods of bringing about a lesser or a greater degree of
dispersion are applicable to all food products. In some cases the effect may
be modified by other factors. It is interesting to trace these through dif-
ferent classes of food products. If alkali is taken as an example, its effects
on some foods may be cited. The alkalies, hydroxides of ammonia, sodium,
and potassium or their basic salts are the ones considered. Calcium and
magnesium salts may have different effects.
Sucrose is little affected by alkalies if they are not stronger than those
ordinarily used in cookery. But when alkalies are added to the mono-
saccharid sugars they bring about decomposition. The sugar in solution is
in the molecular state, and the alkalies cause increased dispersion, even
though the sugar and its decomposition products both remain in molecular
dispersion. The properties of the decomposition products are different
from those of the original sugar.
Vegetables and fruits are softened by the addition of alkalies during
6 RELATION OF COOKERY TO COLLOID CHEMISTRY
cooking, and they may become mushy and disintegrate. This is probably
due to the greater dispersion of the cellulose and pectic substances. In dried
legumes, alkalies may also increase the disintegration of some of the protein.
Milk is prevented from curdling or coagulating by the addition of alkali.
Curdling is a lessened dispersion of the milk protein, casein. The addition of
alkalies to eggs elevates the temperature for coagulation. Alkalies added
to doughs cause a greater degree of dispersion of the gluten, which results
in a dough that is runny and sticky to handle. In larger quantities the bak-
ing quality of the flour is partially destroyed. Alkalies added to gelatin
tend to prevent its setting, and they may cause greater dispersion in emul-
sions.
Dispersion by enzymes. Enzymes may also cause an increased or
lessened degree of dispersion in foods. The clotting of milk upon the ad-
dition of rennin is an example of lessened dispersion, but the proteinase
enzyme in flour increases the dispersion of the gluten.
Classification and Properties of Colloids Based upon
Physico-Chemical Relationships in Liquids
Each colloidal solution as well as each true solution has its own peculiar
properties. These depend upon the nature of the particles in solution and
the dispersing medium. But a large group of colloidal systems may have
similar properties, and for convenience they are classified in a group or
subdivision. The classification of colloidal systems into groups is not
always satisfactory, for there is no distinct line of demarcation between
the different subdivisions. Ostwald, Freundlich, Gortner, and Buchanan
and Fulmer give excellent discussions of the properties of colloidal systems
which are of interest to those concerned with food preparation.
Suspensoids and emulsoids. One basis for classification of colloidal
systems is the nature of the dispersed phase. In a suspensoid the dispersed
particles are in a solid state. In an emulsoid the dispersed particles are in a
liquid state. Many authorities classify suspensoids and lyophobes, emulsoids
and lyophiles, as being coextensive, but Freundlich states that this is in-
correct, for there are many emulsoids with lyophobic properties.
Reversible and irreversible colloids. If after a colloidal solution is
evaporated, a sol is reformed upon the addition of water, the colloid is
classified as a reversible colloid. Gelatin and dried egg white are examples
of this type of colloid. An irreversible colloid does not spontaneously form
a sol with the addition of water, after water has been evaporated. Re-
versible and hydrophilic colloids are coextensive; irreversible and hydro-
phobic colloids belong to similar groups.
Sols and gels. Colloidal solutions are also classified upon the basis
of their consistency. Those which are apparently solutions are called sols.
Those with a jelly-like consistency are called gels. The consistency of fruit
jelly or a gelatin dessert is that of a typical gel. There is no distinct line
SWELLING OF COLLOIDAL GELS 7
of separation between sols and gels, nor on the other hand, according to
Jordan Lloyd, between gels and curds. The classification of gels on the
basis of consistency includes many gels that do not have similar proper-
ties. Some gels are formed from sols by coagulation. Custard is an ex-
ample of this type. A starch gel is formed by gelatinization of the starch
during cooking. Gelatin, agar-agar, and soaps form sols above certain
temperatures and gels at lower temperatures. Such gels are called revers-
ible. The sol-gel transformation is brought about gradually, there being
no definite melting or setting temperature. The change from a sol to a gel
by cooling is termed gelation and is a distinct process from that of coagu-
lation. Temperature, time, concentration, and the presence of electrolytes
or non-electrolytes are factors in gel formation. There are various theories
regarding gel structure, but space does not permit considering them here.
It may be added that there is a similarity between crystallization and
gelation. Jordan Lloyd states that "gelation is a process closely parallel to
crystallization and is accompanied in most cases by evolution of heat." One
other factor of similarity is that with rapid cooling a finer structure of the
micelles is obtained.
Swelling of colloidal gels. Freundlich designates the gels that may
imbibe a liquid and give it up as turgescible, and those which do not swell
as non-turgescible. The imbibition of water is known as turgescence; the
giving up of water is designated as deturgescence. The term hydration is
used to indicate imbibition of water by the micelles ; solvation is the general
term used for all liquid dispersion mediums. The lyophilic colloids are
characterized by their affinity for their dispersion mediums. Whether the
micelles of gelatin, agar-agar, etc., actually act as a solvent for the inter-
micellar liquid, or whether the liquid is attracted and bound, probably
by electrical forces, to the surface of the micelle in the form of a shell is
still a disputed question. The amount of water that can be held by many
of the micelles in the form of a shell around the particle is relatively enor-
mous. As the concentration of the micelles is increased, the viscosity of the
solution increases, owing to a larger portion of the dispersion liquid being
bound. A concentration of 0.75 per cent of pectin micelles gives a fruit
jelly of good texture. Increasing their concentration gives a stiffer jelly.
The molecules of the dispersion medium are probably oriented in a definite
manner around the micelle, for the volume of a gelatin gel is less than the
combined volume of the dry gelatin and the water.
The ability of the micelles to take up and hold water is important in
food preparation. The thickening of a cup of milk by an egg in a custard
is due to the ability of the egg proteins to bind the liquid. The thickening
power of starches is due to the swelling of the starch granules during heat-
ing. The ability of proteins, starches, etc., to imbibe water is very great.
A pressure of 2500 atmospheres is required to prevent the swelling of starch
when it is heated in water. Gortner defines imbibition pressure as "the
pressure against which such a colloid will imbibe a liquid, or conversely the
8 RELATION OF COOKERY TO COLLOID CHEMISTRY
pressure which is required to force the dispersions medium out of a gel.
Imbibition pressures should not be confused with osmotic pressure, and in
many instances they assume values greatly in excess of values obtainable
by osmotic pressure. If a sheet of dried gelatin is placed in a saturated
solution of sodium chloride, water will be withdrawn by imbibition forces
against the osmotic pressure of the sodium chloride solution, and sodium
chloride will crystallize out in the solution."
The micelles possess either a positive or a negative charge. When the
electrical forces holding the bound water to the micelle are neutralized, as
may happen when electrolytes are added under suitable conditions, the
bound water is released and the viscosity of the system decreases. When
a custard is curdled the bound water is set free. The ability of muscle fibers
to hold water during cooking prevents drying of the meat to a great extent.
Effect of added substances upon swelling of gels. The addition
of such substances as acids, alkalies, mineral salts, and sugar may increase
or inhibit the degree of swelling. Many such combinations are made in
cookery. Lemon juice and vinegar may be added for flavor. Soda, salt, and
baking powder may be added to foods. Different proportions of mineral
salts are found in foods, and the proportion may vary in the same food
owing to many causes. In general, the addition of acids or alkalies increases
the swelling of colloidal gels. With acids, this usually continues until a
maximum is reached at pH 3.0 to 2.5, when imbibition is decreased with
greater acidity. With alkalies the maximum swelling is about />H 10.5,
though gluten gels are likely to disintegrate when they become as alkaline
as this. Sometimes the addition of acids or alkalies lessens hydration. This
depends upon the pH of the substance when the acid or alkali is added.
In general, salts lessen the degree of swelling even in the presence of acids
or alkalies.
Syneresis. After gels are allowed to stand protected against evapora-
tion for a number of hours there is a tendency for the gel to separate into
two phases. A liquid may squeeze out of the gel. A typical example is the
separation of the whey from the curd in clabbered milk. It is also noticed
in some jellies, cranberry jelly in particular. This separation into a more
solid and a more liquid part may take a long time in the case of some food
gels, a shorter time in others. In syneresis the liquid part contains a large
proportion of the solvent, a smaller proportion of the solid. The more solid
part has a high concentration of the solid, a lower one of the solvent.
Hydrophilic and hydrophobic colloids. The terms lyophilic and
lyophobic include all dispersing mediums whereas hydrophilic and hydro-
phobic indicate that the dispersing medium is water. Hydrophilic means
"water loving"; hydrophobic means "water hating." The lyophilic colloids
belong to the liquid dispersed in liquid systems, though as pointed out by
Gortner and by Fischer this terminology is not strictly accurate, for the
dispersed phase and dispersing medium are more or less soluble in each
other. Thus, with gelatin and water, hydration occurs or the two are
ELECTROLYTES AND HYDROPHOBIC COLLOIDS 9
mutually more or less soluble in each other. The chief differences between
hydrophilic and hydrophobic colloids are their degree of hydration and their
reaction to electrolytes. The particles of a hydrophilic colloid require the
addition of a large quantity of an electrolyte to bring about coagulation,
whereas the hydrophobic colloids are sensitive to, and coagulated by, very
small quantities of electrolytes. Gelatin, agar-agar, starch, and protein solu-
tions belong to the hydrophilic group; the metal sols belong to the hydro-
phobic group. There is no distinct line between the hydrophilic and hydro-
phobic colloids. Even the particles of the rather typical hydrophilic colloids
are not hydrated to the same extent. Thus an agar-agar sol is more strongly
hydrated than a gelatin one. Another way of expressing this is to say that
about 1 per cent of agar-agar will form a stiff gel, but more than 1 per cent
of gelatin is required for a stiff gel.
The charge on colloidal particles. That the micelles possess either a
negative or a positive charge is agreed, though the origin of the charge is
still disputed. For aqueous solutions the charge is most easily explained on
the basis of adsorbed ions. The charge may also come from ionization
of the micelle, or by electrification by contact with the dispersing medium,
in the same manner that a glass rod becomes charged when rubbed with
fur. If the charge on the micelles is reduced to practically zero, the col-
loidal system becomes unstable. The electrical charge is one important
factor in the stabilization of sols. One example in foods is the casein of
milk. When the electrical charge of casein reaches zero, the protein floc-
culates and is precipitated. Kruyt cites it as an example of a protein sol
that is not sufficiently hydrated to be stabilized by hydration alone, so that
it can exist when negatively or positively charged, but not when the charge
is neutralized.
Freundlich uses the term electrokinetic phenomena to designate certain
electrical properties of colloidal systems. He also states that these electro-
kinetic phenomena are closely associated with the physical properties of
interfacial tension, adsorption, colloidal stability, mutual precipitation, and
flocculation.
The theories that have been advanced to explain electrokinetic phenom-
ena are based upon the double-layer theory of Helmholtz. This theory is
that the micelle is surrounded by a double layer of ions, the inner layer,
which may be negative or positive, being closely adsorbed by the micelle,
and the outer layer, consisting of ions of opposite charge from those of the
inner layer, lying close to the micelles in the intermicellar liquid. If the
inner layer of ions is negative, the micelle is negatively charged, the outer
layer being positively charged. As the colloid passes through its isoelectric
point the charge of each double layer is reversed.
Effect of electrolytes upon hydrophobic colloids. When a hy-
drophobic colloid is coagulated by an electrolyte its electric charge is
removed. The amount of electrolyte required depends upon several factors:
( 1 ) The manner of adding. More electrolyte is required if it is added in
10 RELATION OF COOKERY TO COLLOID CHEMISTRY
small portions than if added all at once. (2) The valence of the ion bring-
ing about the coagulation. Coagulation is brought about by the ion having
the opposite charge to that of the colloid. As a general rule, the precipitat-
ing effect is increased with an increase of valence of the ion bringing about
the coagulation. There are exceptions to this rule, as some monovalent ions
have greater effect in bringing about coagulation than some polyvalent
ions. (3) Concentration of the electrolyte. In many cases there are zones in
which a definite concentration of the electrolyte brings about maximum
coagulation. Higher or lower concentrations are not so effective or may not
bring about coagulation. This is illustrated later in egg cookery. High con-
centrations of ferric or aluminum chloride do not bring about coagulation
of distilled-water custards but small concentrations cause coagulation.
(4) The concentration of the colloid also affects the amount of electrolyte
required for coagulation. (5) A definite time may be required, depending
upon the concentration of the protein and electrolyte.
Effect of electrolytes upon hydrophilic colloids. The effect of
electrolytes upon hydrophilic colloids is varied. Kruyt states that the hydro-
philic colloids are stabilized by two factors, the electric charge and the
strong hydration of the particles, and after the hydrophilic colloid is
dehydrated it is as sensitive to electrolytes as the hydrophobic colloids.
Dehydration of the hydrophilic colloids may be brought about by different
means. Some proteins may be dehydrated by heating. Alcohol may be
used to dehydrate hydrophilic colloids, and tannins may also bring about
dehydration. This dehydration by heating or other means is called denatur-
ation. If an egg white is dialyzed and the electrolytes removed it is not
coagulated when heated. But the addition of electrolytes to the heated
dialyzed egg white brings about coagulation. Kruyt states that if small
quantities of electrolytes are added to a starch or agar-agar sol the electric
charge is removed but the colloidal particles do not precipitate. If alcohol,
a dehydrating agent, is added to the above starch or agar-agar sol, coagu-
lation occurs. It is immaterial in which order the two stability factors, the
electric charge and hydration, are removed. The removal of one has no
evident effect, but the removal of both factors causes coagulation. The term
denaturation will be used in later references to indicate sensitization of
hydrophilic colloids to electrolytes. The term denotes whatever changes are
brought about during dehydration of the colloid.
The action of electrolytes upon proteins is given as follows by Buchanan
and Fulmer.
"1. Those electrolytes which bring about a reversible precipitation
in high concentration. These include the salts of the alkalis, K, Na,
NH4, Li and possibly Mg. Ammonium sulphate is commonly used
in 'salting out' of proteins. The precipitate so formed will be redis-
solved on dilution, i.e., the process is reversible.
"When the protein is on the alkaline side of its isoelectric point (i.e.,
ISOELECTRIC POINT 11
negatively charged), the order of effectiveness of the salt is on the
basis of cations : Li > K > Na > NH 4 > Mg and of anions, citrate
> tartrate > SO 4 > acetate > Cl > NO 3 > C1O 3 > I > SCN.
"2. Those electrolytes which bring about an irreversible precipita-
tion in concentrated solutions. These include the salts of alkaline
earths, Sr, Ba, Ca, and possibly Mg.
"The order of effectiveness for negatively charged protein is Ba >
Ca > Sr and acetate > Cl > NO 3 > Br > I > SCN with the re-
verse order for the positively charged protein.
"3. Those electrolytes which in low concentrations bring about an
irreversible precipitation. These include the salts of the heavy metals
such as Ag, Hg, Fe, Cu. An interesting characteristic of this group
is the fact that two optimal zones may be found. For instance, copper
sulphate solutions precipitate albumin in concentrations from
0.001 N 1 2V, in higher concentrations the precipitate redissolves, a
precipitate appearing again at a concentration of 6 N. Zinc salts show
maximal precipitation at 0.01 2V 0.5 N and again at 42V."
Protective and denaturating colloids. A substance that tends to
prevent coagulation of micelles is designated as a protector; if it is in the
colloidal state it is called a protective colloid. Sometimes small amounts
of a colloid sensitize instead of protecting. The latter are sometimes called
denaturating colloids.
Amphoteric colloids. Substances that combine with either acids or
bases are known as amphoteric substances. Proteins belong to this group.
They are composed of amino acids. The amino acids contain amine
( NH 2 ), and carboxyl ( COOH), groups. The - NH 2 groups
combine with acids; the COOH groups combine with alkalies. Most
of the NH 2 and COOH groups are linked or bound in forming the
protein molecule, but some are free, and combinations with acids and bases
are formed with these free groups.
Isoelectric point. At a definite acidity or />H for each protein, there
is a point called the isoelectric point. The />H of different proteins at the
isoelectric point varies because of the different amino-acid content of each
protein, which results in a larger or smaller number of NH 2 or
COOH groups. At the isoelectric point the protein is combined with
neither anions nor cations or else it is combined with both equally, for the
charge is neutral. Thus at the isoelectric point in a cataphoresis experiment
the protein does not migrate to either the anode or cathode. At the iso-
electric point certain characteristic properties of the protein are at a mini-
mal, i.e., it is most easily precipitated by electrolytes, is least soluble, shows
the least viscosity, is also less dispersed, and least stable as a colloidal solu-
tion. Other minimum points at higher acidity or alkalinity than the isoelec-
tric point are not considered in this discussion, for they are found less
frequently in food preparation.
12 RELATION OF COOKERY TO COLLOID CHEMISTRY
Combinations of proteins with alkalies. At a />H above its iso-
electric point the protein combines with alkalies to form such salts as
sodium proteinate, calcium proteinate, etc.
NH 2 NH 2
R-C + NaOH -- R-C + H 2 O
COOH COONa
protein sodium sodium proteinate water
hydroxide
Combination of proteins with acids. At a />H below the isoelectric
point or on the acid side the protein combines with acids to form salts such
as protein chlorides. Here the effect is additive and similar to the addition
of hydrochloric acid to ammonia to form ammonium chloride.
NH 2 NH 3 C1
R-C + HC1 -> R-C
COOH COOH
protein hydro- protein chloride
chloric
acid
Combinations of proteins with acids or alkalies in food prep-
aration. Many combinations of proteins with acids or alkalies are formed
in food preparation. Most alkaline salts of the proteins are soluble. Some of
the acid salts are soluble; others are difficultly soluble. Casein, the protein
present in rnilk in the largest quantity, has a pH of 4.7 at its isoelectric
point. Casein in sweet milk is found as an alkaline salt. Fresh milk has a
/>H of 6 to 7. If an acid is added to the milk the casein will be precipitated
when the reaction of the milk reaches the isoelectric point of the casein,
pH 4.7. This occurs in natural souring by the formation of lactic acid
in the milk. Familiar examples of combinations of acid with milk are the
addition of lemon juice to milk for sherbet or the addition of tomatoes to
milk for cream of tomato soup. If enough acid is added to lower the reac-
tion of the milk below the isoelectric point of the casein, an acid salt is
formed. If this salt is soluble, the curds of casein will dissolve. This change
of the protein from an alkaline to an acid salt often occurs in making may-
onnaise and other salad dressings. The addition of a small amount of acid
to egg yolk will curdle it, but upon the addition of a little more acid the
curd may dissolve.
Stoichiometrical combination. Stoichiometrical combination means
that the reaction between compounds is carried out according to the laws
of valence. Loeb and others working with dilute solutions of proteins,
acids, alkalies, and salts showed that proteins combine with acids and al-
kalies in Stoichiometrical relationship. But Hoffman and Gortner have
shown that proteins in stronger concentrations of acids or alkalies adsorb
SURFACE TENSION 13
acid or alkali. This means that owing to the surface area and the physical
property of adsorption the proteins can combine with larger quantities of
acids or alkalies than is possible in stoichiometrical combination alone.
Boundary Phenomena
Because of the size of micelles, surface phenomena assume an important
place in colloidal reactions. Surface tension, the formation of foams, inter-
facial tension, adsorption, formation of surface skins, orientation of mole-
cules, cohesion, and adhesion all have application in food preparation. Dif-
ferent authorities use a different terminology to designate the chemical and
physico-chemical processes taking place at the interface between two phases.
Kruyt calls them boundary phenomena, Freundlich designates them as
capillary chemistry, and other authorities use other terms.
Total surface area increases in proportion to the increase in number and
decrease in size of the micelles. Molecular systems have proportionally a
greater surface area than colloidal ones, but, on account of the small size
of the particles, other forces have a greater effect than surface ones in
molecular systems.
Freundlich states that "The subject of capillary chemistry may be divided
into natural subdivisions, according to the nature of the interfaces which
separate the various possible pairs of phases. We can distinguish the follow-
ing interfaces: liquid/gaseous, liquid/liquid, solid/gaseous, solid/liquid,
solid/solid. Because of the complete rigidity of the interface between two
solids, the section relating to this pair drops out."
Surface tension. Arbitrarily, surface tension refers to the tension
of a liquid/gas interface. Liquids like gases possess kinetic energy, but un-
like gases they have a surface or a boundary layer. This boundary layer
gives a liquid certain properties that gases do not have. Surface tension is
the result of the inherent property of a fluid to tend to form a minimum
surface under all conditions. The minimum surface for a given volume is
in the form of a sphere ; hence, when free to do so liquids assume a spheri-
cal shape. Small drops of water falling on a dusty surface or a waxy leaf
tend to form in drops. Large drops are flattened by gravity. When drops
of water fall on a surface like clean glass, they spread and wetting occurs.
The forces acting between the clean glass and the liquid prevent the liquid
assuming a spherical shape.
The molecules in the interior of a homogeneous liquid do not exhibit any
surface-tension phenomena in relation to one another since they are sub-
jected to a balanced attraction. That is, they are equally attracted by other
molecules on all sides. But the surface film is in a state of tension due to
the unbalanced attractions of the molecules at the surface. The molecules
are attracted only downward and sideways. Whereas the molecules in the
interior of the liquid are evidently arranged at random, those in the surface
are oriented or arranged in a definite and orderly manner. Freundlich
14 RELATION OF COOKERY TO COLLOID CHEMISTRY
states that it is only a step to conceive that this tendency to form a mini-
mum surface resides in a membrane. Kruyt speaks of a boundary layer.
The tension of this membrane is the so-called surface tension of the liquid.
Surface tension is defined by Buchanan and Fulmer as "the amount of
work required to produce a new surface of unit area at constant tempera-
ture." To enlarge the surface of the liquid requires work. The amount of
work expended to enlarge a surface multiplied by the area increased is
termed free surface energy. The amount of work to enlarge a surface is
greater with increased surface tension. Just as the surface area of a liquid
tends to assume a minimum surface through its inherent surface tension,
so free energy tends to assume a minimum value. The free surface energy
is decreased (1) by reducing the surface area or (2) by reducing the sur-
face tension. Hence, small drops of liquid will unite with large drops if
they are within the same space so that they are connected by their vapor,
thus reducing the surface area.
Water has a high surface tension. Surface tension is measured in dynes
per centimeter. The surface tension of water at 18C. is 73.0; that of ethyl
alcohol, methyl alcohol, and chloroform at 20C. is 21.7, 23.0, and 26.7,
respectively. The surface tension of mercury at 15C. is 436.0. Surface ten-
sion decreases with increase in temperature, becoming zero at the critical
temperature.
The surface tension of solutions. When a substance is dissolved
in a pure liquid the surface tension of the solution may not be changed,
it may be raised, or it may be lowered. The substances that scarcely change
the surface tension or elevate it slightly include the aqueous solutions of
most electrolytes and some organic compounds. Sugar increases the surface
tension of water. Freundlich calls these substances capillary-inactive or
surface-inactive. The group of substances that lower surface tension in-
cludes in aqueous solutions many organic compounds such as aldehydes,
fatty acids, fats, acetone, amines, alcohols, tannins, saponins, and proteins.
Freundlich calls this group of substances capillary-active or surface-active.
If a substance lowers or increases the surface tension, the effect is always
increased with its concentration. Surface tension can be lowered tremen-
dously, but it can be raised to only a slight extent. If a substance lowers
the surface tension its concentration is greater in the boundary layer than
in the bulk of the liquid ; and, conversely, if the substance raises the surface
tension the concentration is less in the boundary layer.
Substances like the fatty acids, formic, acetic, propionic, and butyric,
etc., that belong to a homologous series, show an increased lowering of the
surface tension as the series is ascended, if they are kept at the same con-
centration. This regularity of increase with such a series is known as
Traube's rule.
Formation of foams. Absorption at liquid/gaseous interfaces.
A foam is a dispersed gaseous phase, the dispersing medium often being a
liquid. The solutions of substances that lower surface tension are apt to
INTERFACIAL TENSION OF LIQUIDS/LIQUIDS 15
froth. Freundlich states that the formation of a foam is a complicated
phenomenon. "Whilst in most other colloidal structures the particles of the
disperse phase are of colloidal minuteness, this is by no means essential
or even usual, in the case of foams. On the other hand the dispersion
medium is often of colloidal fineness, that is, the gas bubbles are separated
from one another by liquid films, having a thickness of only a few m//,.
Hence in a foam the surface of a liquid has been enormously extended,
which is in opposition to the tendency of surface tension to make the sur-
face a minimum. For this reason a liquid must fulfil a number of special
conditions. In the first place the surface tension of the liquid must be
small, for otherwise its tendency to reduce the surface would be too power-
ful." A second condition for the production of stable foams is that the
vapor pressure shall be small, for substances with high vapor pressure
evaporate rapidly. The surface films must not coalesce readily. These con-
ditions are fulfilled by aqueous solutions of capillary-active substances, and
especially by sols of many colloids, like soaps, saponins, tannins, and
proteins. Freundlich states that in protein solutions a third influence plays
a part, for they have the property of forming thin "pellicles" or surface
skins on the boundary layer, which tend to prevent evaporation. Since
the substance that lowers surface tension of the liquid is found in greater
concentration in the foam, if the foam is continually removed as it is
formed, the greater portion of the protein or other substance is removed.
This is applied in the following and similar ways. In making sorghum
molasses, in order to have a delicate-flavored product, one must have
"a good boil" and remove the scum forming on the surface. In this way,
tannins, which would increase the bitterness of the sorghum, proteins, and
other substances are removed.
Rahn has shown analytically the results of the application of "the law of
Gibbs and Thomson which states that substances which cause a depression
of surface tension will accumulate in the surface. In a gelatin solution,
there is more gelatin in the very surface layer than in the center of the
solution." In a milk foam the concentration of protein is greater in the
foam than in the solution. The analytical results of Rahn are given in
Table 2.
Rahn states that "If protein is concentrated on the surface it has a
tendency to become solid, but all proteins do not behave alike. Some
solidify rapidly, others slowly, and some do not solidify at all. Quite often,
this solidification is irreversible, and the protein, when put back into the
solution, will not dissolve again." When milk foams, solid walls form
around the air bubbles and, when the foam settles, these walls of protein
can be seen with the aid of a microscope.
Interfacial tension of liquids/liquids. When two non-miscible
liquids are poured together, one liquid forms a layer on top of the other,
thus making a liquid/liquid boundary. The less the solubility of the two
liquids in each other, the greater their interfacial tension ; but most liquids
16 RELATION OF COOKERY TO COLLOID CHEMISTRY
TABLE 2
COMPOSITION OF SKIMMED MILK AND ITS FOAM (Rahn]
Constituent of
the milk
Average of 9 experiments
with intensely foaming
skimmed milk
Average of 6 experiments
with slightly foaming
skimmed milk
Liquid part
%
Foam
07
%
Liquid
%
Foam
%
Protein
3.09
4.85
0.75
3.51
4.73
0.78
3.01
4.92
0.74
3.24
4.92
0.76
Fat and lactose
Ash
Total solids
Protein increase in the
foam
8.69
9.02
13.6
8.67
8.92
7.6
are not completely insoluble in each other. Just as a substance may con-
centrate at a liquid/gaseous interface, so likewise those substances which
decrease interfacial tension tend to concentrate at a liquid/liquid or a
liquid/solid interface. With the addition of a third substance soluble in
water, Traube's rule holds, but if it is more soluble in the second liquid
then the lowering of the interfacial tension is small and Traube's rule
scarcely applies.
Adsorption. Adsorption has been defined as the concentration of a
substance at an interface. The increased concentration at the interface is
designated as positive adsorption ; a decrease in the boundary layer is called
negative adsorption. The amount adsorbed depends on the concentration
of the material being adsorbed and the extent of the surface at which it
can be adsorbed. The importance of surface reactions or phenomena can-
not be over-emphasized in food preparation. Lowering of interfacial tension
aids in the forming of emulsions. Fat is strongly adsorbed by sugar crystals,
and when the two are mixed this aids in distributing the fat throughout
the batter.
Bancroft states that peptization is always due to adsorption. Since peptiza-
tion occurs frequently in food preparation, additional mention should be
made of it here in connection with adsorption. Bancroft states that theo-
retically there are three possibilities when adsorption occurs at a surface.
(1) If an adsorbed film has a low surface tension on the water side and a
high one on the other side, it will tend to scrunch up and to peptize the solid
as internal phase. (2) If the reverse is true, the -solid will tend to form the
external phase. (3) If the two surface tensions are equal, neither will pre-
ORIENTATION OF MOLECULES 17
vail. Many instances of peptization might be mentioned. There is the pre-
vention of coagulation by heat of peptizating action of sugar on egg pro-
tein. There is the peptizing action of soda on flour proteins with increasing
tenderness of the product. This occurs in the chocolate cake known as
devil's food when excess soda is used.
The interfacial tension of solids/liquids. Adsorption is very pro-
nounced at the interface between these two phases. Just as small drops of
a liquid will unite through their vapor to form larger drops, thus reducing
the free surface energy and their surface area, so small crystals in a super-
saturated solution will unite to form larger crystals. Small crystals have a
greater solubility than large crystals. They also have a greater surface area
than the large ones per unit mass, thus a greater surface energy. Since
surface energy tends to a minimum, equilibrium can be reached only by
establishment of larger crystals in the solution. A discussion of the growth
of crystals in fondant and similar candies during storage is given later.
Formation of surface skins. Bechhold states that one characteristic
of colloidal systems is the forming of a surface skin. This may be similar
to the formation of a boundary layer in a liquid. Staining solutions form
a scum on the surface that must be removed by straining before using.
In food preparation this surface skin may be due to a change, as coagulation
of a portion of the egg by beating or coagulation of proteins by heating.
Whatever the cause, beaten eggs and egg yolks form surface skins after
standing a short time, which is not entirely due to a drying of the surface.
Boiled milk forms a pronounced skin during heating and after cooling.
Orientation of molecules. The molecules at an interface do not
lie at random but are oriented or arranged in a definite manner. The
arrangement assumed depends partly upon the arrangement of the atoms
in the molecule. Molecules of ethane (CH 3 .CH 3 ), butane, and pentane
are symmetrical, i.e., in each molecule the two ends are identical. In acetic
acid (CH 3 .COOH) the two ends of the molecule are unsymmetrical. In
ethane the two ends would behave the same at an interface, but this would
not hold for acetic acid. The (CH 3 ) group is called a non-polar group;
the (COOH) group, a polar one. At the air/ water interface polar groups
always orient away from the air and towards the water, for water has
pronounced polar characteristics. "Like attracts like" is a rule that all
students of organic chemistry have learned. In general, the polar liquids are
miscible, but slightly polar liquids are relatively insoluble in polar liquids.
A substance like acetic acid, containing a short hydrocarbon chain and a
polar group, is completely miscible with water, for the (COOH) group is
attracted to the water so strongly that the hydrocarbon chain is also
dragged into the water. When two (CH 3 ) groups are attached to the
(COOH) group, the solubility is lessened, and with increasing length of
the hydrocarbon chain solubility in water progressively decreases. Thus the
possession of a polar group confers upon the substance a certain solubility
in water, and the possession of a non-polar group may confer upon it a
18 RELATION OF COOKERY TO COLLOID CHEMISTRY
greater solubility in some other solvent. Orientation occurs at the interface
of two liquids, such as emulsions. Polar groups are those containing oxygen,
nitrogen, sulfur, or iodine. Thus substances containing (COOH),
(CHO), or (NH 2 ) groups, or double bonds, contain polar groups. Polar-
ity is based upon the concept that some parts of a molecule may have
gained while other parts may have lost one or more electrons. This results
in differences in charges at a small distance apart. The polar groups or
polar substances are reactive; the non-polar groups or substances are more
inert.
Cohesion. Cohesion refers to the property of a substance whereby
the particles of a body are united throughout the mass. The particles as a
unit resist being torn apart.
Adhesion. Adhesion refers to the attraction whereby the surface of
a substance sticks to the adjacent surface of another substance. Drops of
water adhere to glass, and the dough adheres to the sides of the container
in which it is placed. Pans for sponge and angel cakes are not greased, so
that the adhesion of the cake mixture to the sides of the pan will aid
expansion of the cake.
Coagulation of Proteins
The term denaturation is used more frequently than coagulation by
scientific investigators at the present time to denote certain changes in
proteins. Definite characteristics of the proteins are changed when they
are coagulated, among which is loss of solubility in water and dilute salt
solutions. In some instances and under certain conditions the coagulation
process may be reversible.
Manner in which denaturation may be brought about. Coagula-
tion of proteins may be brought about by a variety of processes. In cookery
one of the principal means of coagulation is heat. But in addition to heat
the action of acids, alkalies, salts, alcohol, mechanical agitation, radiation,
and ultra-sonic vibrations may denature the protein and convert it from a
soluble into an insoluble form.
Some changes in the proteins during denaturation. All investi-
gators agree that denaturation is brought about in two steps. The first step
is a preliminary alteration of the protein or denaturation. The second is a
physical change which leads to coagulation or aggregation. Clayton in
discussing "Foods as Colloid Systems" reviews some of the theories of
protein denaturation. "Hydrolysis has been frequently reported as the
cause of denaturation, but present views incline to the idea of some struc-
tural rearrangement within the molecule. Thus, the refractive index in-
creases during heat denaturation, whilst X-ray diffraction patterns lead
to the view that coagulation is accompanied by the elimination of water
between NH 2 and COOH groups. . . . Cubin holds that denaturation is
the distortion or opening up of the protein unit, whilst flocculation is the
HEAT COAGULATION 19
process following this and rendered possible by it. Interaction of NH 2 and
COOH groups situated on contiguous colloid units leads to aggregation
and, hence, coagulation."
No matter how denaturation is brought about, the denatured product
has sulfur atoms, the combination of which differs from those in the native
protein. Mirsky and Anson have shown that in native egg albumin no
sulfhydryl (SH) and disulfide (S-S) groups are detectable by certain
methods. But in completely coagulated protein the number of SH and
S-S groups detectable is the same as in hydrolyzed protein. These workers
have also shown that in partially coagulated protein when the soluble and
insoluble fractions are separated the soluble portion contains no detectable
SH or S-S groups, but the insoluble fraction has the number of reactive
SH and S-S groups characteristic of the completely denatured protein.
In the interfacial coagulation of a protein, i.e., when a film of insoluble
protein forms at the surface of a protein solution, SH and S-S groups
appear, the number being the same as that found in the hydrolyzed protein.
Also when the proteins are denatured by ultra-violet light, by acids, or by
other means the SH and S-S groups appear. From these results they con-
clude that the formation of insoluble proteins and increase in detectable
SH and S-S groups are closely linked phenomena; that denaturation is a
definite chemical reaction; and that a given protein molecule is either
completely native or completely denaturated.
In a later paper Mirsky and Anson report that the number of detectable
SH and S-S groups in different proteins varies with the pH and the tem-
perature. To illustrate, native hemoglobin had no detectable SH groups
at pH 6.8. But with increase of pH the SH groups become detectable
in increasing numbers up to pH 9.6. But native egg albumin showed no
detectable group at pH 6.8 or pH 9.6. However, denatured hemoglobin
had detectable groups at pH 6.8 and still more at pH 9.6. They found
that intact, unhydrolyzed proteins possess in addition to SH groups other
reducing groups which can be oxidized by ferricyanide. The number and
activity of these groups vary from protein to protein. They are probably
contained in the tyrosine and tryptophane component of proteins. "It can
now be seen that the activation of SH and S-S groups in protein denatura-
tion is part of a more general process."
Heat coagulation. As has been indicated heat coagulation of proteins
is used in preparation of food products, and, fortunately for the mental
equilibrium of the cook, heat coagulation of proteins is ordinarily not
reversible. Otherwise, many cooked dishes would, with certain treatment,
revert to their original uncooked consistency.
Some of the changes occurring during heat coagulation of the proteins
have been indicated. But these are not the only factors playing a role in
the process. Electrolytes have some role in heat coagulation of proteins.
This is shown in the work with distilled water egg custards. It has been
shown that, if the mineral content of egg white is lowered through dialysis,
20 RELATION OF COOKERY TO COLLOID CHEMISTRY
coagulation does not occur on heating. The effect of electrolytes in heat
coagulation may be brought about either by chemical reaction or by
adsorption. If the effect of salts is brought about by adsorption, the salts
must be very strongly adsorbed and almost impossible to remove from the
aggregated protein by washing the protein, for the process is usually
irreversible. Any theory of heat coagulation of the proteins must not only
explain how the proteins are rendered insoluble by heat but the effect of
other factors. That the heat coagulation of proteins is influenced by
electrolytes, sugar, temperature, time, the reaction of the solution, and the
presence of water and other factors is evident when the cooking of eggs,
custards, salad dressings, cheese and egg dishes, baked products, and meat
is observed. The effect of some of these factors can be determined in the
laboratory; but the understanding of the manner of their action is lacking
in many instances and awaits explanation by the colloid chemist or bio-
chemist.
Bancroft and Rutzler have reported that heat-coagulated egg white
may be peptized by dextrose and certain salts. They showed that the
coagulated and repeptized egg-white sols are identical with the original
solution by immuno-biological tests for species specificity and isoelectric
point measurements. Because of the similarity of the reversed protein to
the original protein they believe that coagulation is a colloidal reaction
which is due to a physical rather than a chemical change.
Interfacial denaturation. Proteins are also denatured at interfaces,
typical examples being the insoluble portion of beaten egg white, and froth
or foam on milk. When egg white or milk foams are allowed to remain
undisturbed, they gradually collapse and the wrinkled membranes, skin,
or films may be observed through the microscope. Mention has already
been made that protein can be recovered from a solution by removing the
foam. Denaturation of protein solution occurs by shaking and in some
instances spontaneously, an example being the membrane formed at the
interface of an air/protein solution when no agitation has occurred.
Neurath and Bull state that both heat and surface denaturation proc-
esses involve an unfolding of the peptide chains which in the natural state
are curled up in the interior of the molecule and become stretched out
when the molecule comes in contact with the surface of the bulk of the
solution. The polar groups of the protein molecule, the amino, carboxyl,
the OH groups of the hydroxy acids, the sulfur-containing groups, and
the peptide linkages, have an affinity for water; whereas the non-polar or
lyophobic groups, the hydrocarbon residues, tend to be repelled by water.
Thinking that an interaction between the amino and carboxyl groups
during heat denaturation might diminish the lyophobic or polar properties
of natural protein, whereas an unfolding of the peptide chains by surface
denaturation might expose lyophobic groups to the surface, which in the
native state are buried in the interior, Neurath and Bull measured the
volume contraction of native, heat-denatured, and surface-denatured pro-
PEPTIZATION OF PROTEINS 21
teins. They found that the native protein had the lowest density, heat-
denatured ones were intermediate, and the surface-denatured protein had
the highest density.
This membrane-forming property of protein through denaturation is
important in food preparation, in all products in which beaten egg white
is used, in emulsions, and wherever interfacial reactions occur.
Membranes form readily on the surface of protoplasm and play impor-
tant parts in cell functions. The presence of calcium has been shown to
stiffen the surface membranes in some instances, whereas sodium and
potassium in the absence of calcium tend to soften and dissolve the membrane.
This suggests that salts may also have some influence in surface denatura-
tion and that the salts of flour, egg, and milk used in cooked products may
modify the denaturation at surfaces.
Clayton states that high concentrations of sugar in egg white will pre-
vent surface denaturation, which of course has application in making angel
cakes, meringues, and sweetened souffles.
Peptization of Proteins
Peptization is the reverse process of coagulation. It increases dispersion
and solubility.
Means of bringing about peptization. Peptization may be brought
about by chemical, electrical, and mechanical means or by enzymes. Freund-
lich states that the hydroxyl ion is generally a very effective peptizer. Other
peptizing ions used in food preparation are the citrate, acetate, and tartrate
ions. Peptization brought about by adsorption has been mentioned.
Peptization of proteins. The results of Gortner, Hoffman, and Sin-
clair show that different salts added to wheat proteins in varying amounts
to give the same /H, or in equivalent concentrations, cause peptization
and solution of varying amounts of the proteins. Both cations and anions
form a lyotropic series. They found the anions arranged in the following
order of increasing peptization : F < SO 4 < Q < tartrate < Br < I ; and
for the cations the following order of increasing peptization : Na < K <
Li < Ba < Sr < Mg < Ca. Most of their salt solution extracts of flour
had a />H of 5.0 to 6.0. This would be on the acid side of the isoelectric
point of the flour proteins, and they would be positively charged. When
the solubility of wheat proteins is increased, the tenderness of the result-
ing bread is increased.
Freundlich states that hydrophobic colloids and also solids may be
peptized by suitable electrolytes, but the process does not take place spon-
taneously. It is necessary to divide up mechanically the liquid or solid mass
very finely, in order that the charging action of the peptizing ion may be
effective. In some liquids it is often sufficient to divide them by energetic
stirring.
"Salting-out" of hydrophilic colloids occurs at high concentrations. But
22 RELATION OF COOKERY TO COLLOID CHEMISTRY
at lower concentrations electrolytes frequently bring about peptization.
Freundlich states that this has been investigated particularly in some pro-
teins or mixtures of proteins, it being found clearly in the case of globulins.
Some globulins remain in solution only in the range of their isoelectric
point because of the peptizing effect of electrolytes.
Both the concentration of the electrolyte and its valence affect the extent
of peptization. In general, the peptizing action is increased with increasing
valence. For example, there is little peptization with the chlorine ion, the
sulfate ion peptizes in higher concentrations, and the citrate ion brings
about peptization with low concentrations.
Bound and Free Water
Water plays a very important role in both plant and animal life as a
solvent for sugars, electrolytes, etc., and thus in the translocation of food
material and metabolism products. But in addition to being a solvent
water forms part of the inmost structural portion of the cell. For example,
from muscle tissue, although it is composed of more than 65 per cent of
water, even with considerable pressure only a few drops of liquid can be
pressed. Part of this water is free water, for it contains the dissolved salts,
proteins, and other materials. But as the period after death increases,
changes occur in the tissue, and greater amounts of liquid can be obtained
with pressure. This water, held by the colloidal micelles so that it forms an
intimate part of the material, is designated as bound water.
Not only cells of plants and animal tissues, but starches, proteins of flour,
gelatin, eggs, and other complex compounds such as lecithin have the
capacity to bind water, giving the product certain characteristics. The
free water is designated as that portion of the water in which solutes such
as sucrose and salt can be dissolved. The bound water is that portion
which is held so tightly that not even sucrose will dissolve in it. The
density of bound water is so great that some investigators state it is
equivalent to having a pressure of 10 thousand atmospheres on it. From
this and other properties bound water is often considered as solid water.
Bound water has a very low dielectric constant. Burns states, "All the
physiological colloids have the property of taking in relatively large quan-
tities of water even against enormous pressures, and of holding this water
against even strenuous methods of removal. This 'bound' water stored in
the micropores is under considerable compression, so much so that its
density and all its physical properties are altered."
The compression of the bound water in bulk is probably due to orienta-
tion and packing of the water molecules around the micelles. It has no
appreciable vapor pressure and freezes with difficulty or forms such small
ice crystals that the biological structure is not injured.
Bound water often requires the application of heat and suction to drive
it off. Burns says, "An alumina gel cannot be dried by heating it for 2 or 3
FLUIDITY AND VISCOSITY 23
days at 500 C., yet some relationship does exist between the 'free' and
'bound' water. Under certain conditions as yet undefined, bound water
may become free again, and the reverse." The greater power of some
samples of meat to retain moisture and yet appear firm and less juicy than
other samples cooked under the same conditions is known. Ostwald states
that pork can be distinguished from other meats by the fact that its water-
holding capacity suffers the least change when cooked or dried. In his work
with angel cake Barmore speaks of the crumb of cake baked at higher oven
temperatures as containing as much moisture but apparently binding the
water more securely for it appears more dry.
Fluidity, Viscosity, and Plasticity of Colloidal Systems
Fluidity and viscosity. Bingham uses the term fluidity to express
the opposite of viscosity. A fluid like water yields readily to any force that
tends to change its form, whereas a viscous substance shows some resistance
to flow. Viscosity is one of the important properties of colloidal systems.
As a general rule, the lyophobic colloids show a viscosity but little greater
than that of the dispersion medium, the viscosity increasing only slightly
with increasing concentration of the micelles. But the lyophilic colloids may
show very high viscosities or even plasticity with very low concentrations
of the micelles.
Bingham states that "a mixture of liquids may have an indefinite number
of fluidities dependent upon the method of mixing, in other words, upon
the structure of the liquid." He also states that colloidal solutions show
differences in fluidity due to differences in structure. Thus it is possible that
cake or other batters made with the same materials and the same propor-
tion of materials may show differences in the structure of the finished cake
on account of different methods of mixing, giving different viscosities to
the batter.
Some substances flow readily; others resist flow; and some must have
weight applied to start flow. When a substance tends to resist a shearing
force it may exhibit a flow that is characterized as viscous, turbulent, or
plastic. If the substance entirely regains its original shape, when the shear-
ing stress is removed, it shows perfect elasticity. If the original shape is
not entirely regained and the substance is deformed to an extent directly
proportional to the shearing force, then the substance is said to show
viscosity. This flow that is directly proportional to the shearing force is
called linear flow. By this is meant that if a weight of 1 pound produces
a definite deformation, a weight of 2 pounds produces twice that deforma-
tion. Turbulent flow is the flow obtained when the ratio of the shearing
force to the deformation decreases.
A pure liquid at a given temperature and pressure has a definite fluidity.
The viscosity of water is approximately six times as great at as at
100C. The viscosity of sols usually decreases with an increase in tern-
24 RELATION OF COOKERY TO COLLOID CHEMISTRY
perature, part of this being due to the effect of temperature upon the
intermicellar liquid. Gortner states that in "colloid systems changes due
to temperature are influenced not only by the viscosity of the dispersion
medium but likewise by the effect of temperature on solvation." Thus
gelatin and agar-agar form sols with rather low viscosity at high tempera-
tures when compared to the viscous liquid or plastic gels they form at low
temperatures. Starch usually forms a suspension at low temperatures, and
its decided increase in viscosity or plasticity comes with rapid hydration at
the gelatinization point. Gortner states that heating a starch paste beyond
the gelatinization temperature causes a decrease in viscosity or plasticity.
Electrolytes added to lyophilic systems, often even in traces, cause great
changes in the viscosity of the sol.
The factors affecting the viscosity of lyophilic systems. Gort-
ner adds an eleventh factor, that of rate of shear, pointed out by Sharp
and Gortner, to the ten given by Ostwald that cause variation in the
viscosity of lyophilic systems. They are as follows : ( 1 ) concentration,
(2) temperature, (3) degree of dispersion, (4) solvation, (5) electrical
charge, (6) previous thermal treatment, (7) previous mechanical treat-
ment, (8) the presence or absence of other lyophilic colloids, (9) the age
of the lyophilic sol, (10) the presence of both electrolytes and non-elec-
trolytes, and (11) the rate of shear.
Viscosity is closely related to the consistency of the finished product in
food preparation. So close is this relation in many cases that the ten factors
listed by Ostwald may nearly be taken as ten commandments of food
preparation. Thus the consistency of a custard is influenced by the concen-
tration of egg or the protein micelles; the temperature to which it is
cooked ; the degree of dispersion of the micelles, which is influenced by the
reaction and other factors; the degree of hydration, which is influenced by
reaction, the kind and concentration of salts present, etc. ; the beating
of the egg; the use of milk or water; how long the custard has aged in
addition to the age of the eggs and milk when used ; the kinds and con-
centration of salts in the egg and milk as well as the addition of sodium
chloride and the non-electrolyte sugar.
Since the line of demarcation between sols and gels is not a definite one,
fruit jellies, gelatin, milk, cream, as well as egg dishes, may be added to
the group of foods in which the consistency of the finished product is related
to viscosity. But this does not end the application, for the structure or type
of product in baked goods is closely related to the viscosity of the batter or
dough, which in turn is influenced by all these factors. Of course these
factors or nearly the same ones affect other properties as well as viscosity of
food materials. Thus the extensibility of gluten, the heat coagulation of
proteins, etc., are influenced by many or all of these factors.
Plasticity. Bingham defines plasticity as "a property of solids in virtue
of which they hold their shape permanently under the action of small
shearing stresses but they are readily deformed, worked or molded, under
ENERGETICS 25
somewhat larger stresses. Plasticity is thus a complex property, made up
of two independent factors, which we must evaluate separately." Modeling
clay is plastic. Plasticity is an important property of fats used for cakes,
biscuits, and pastry. A plastic fat has a consistency such that it will form
a thin sheet or layer in a batter or it will retain air bubbles when
"creamed." The enclosing of these air bubbles in the fat is an aid in leaven-
ing cakes and may assist in obtaining a velvety texture, for the enclosing
of the air renders the fat more plastic, thus more easily distributed in the
batter at lower temperatures.
Energetics
Burns states, "Energy is the underlying cause of all changes in matter.
This does not seem a very satisfactory definition, but, so far, it is the only
one possible. . . . Energy, then, is that which produces an effect on our
senses." It is measured by its power to do work.
Energy in some form is often applied to the materials used for food
products. This energy may be electrical, mechanical, or in the form of heat.
An electric current passed through a food may be used to cook it. Very
interesting experiments are being carried out along this line of work by the
Household Equipment Department at Iowa State College. One of the
striking results is the very short time required to cook the food. The pas-
sage of an electric current is used by some companies to pasteurize milk
and by some to sterilize fruit juices.
Mechanical energy is used to beat, stir, fold, knead, or grind food.
The frequency of application of heat to foods does not need to be men-
tioned, for this is what the term to cook means. Foods may be cooked by
radiant heat ; or by transmission of the heat by conduction, i.e., from parti-
cle to particle ; or by convection, which is the diffusion of heat through a gas
or liquid by movement of the gas or liquid particles. A combination of these
methods may be used to transmit the heat. Oven cooking employs all three.
Kinetic energy is due to motion. It may be due to motion of the sub-
stance itself or of the particles composing it. It is directly available for
work. Potential energy is associated with position, i.e., composition, stress,
or strain. Kinetic energy is necessary to liberate it to perform work.
Just as matter is indestructible, though its form may be changed, so is
energy indestructible. This constitutes the first law of thermodynamics.
The law of Hess states that the amount of heat generated by a chemical
reaction is the same whether it takes place all at once or in steps.
The second law of thermodynamics concerns the degradation or dissipa-
tion of energy. In practise, some of the freed energy is converted into heat,
which is diffused among the surrounding objects, and, so far as work is
concerned, is lost. Burns states the law simply: "Every change takes place
at the cost of a certain amount of available energy." He adds that the
second law lends itself to the deduction that the cause of all change is the
26 RELATION OF COOKERY TO COLLOID CHEMISTRY
tendency of energy to attain the same uniform degree of intensity as that
of its environment. This means that any system tends to change to the
most stable state.
Bread during baking tends to attain a physico-chemical equilibrium. But
the temperature attained during baking is much higher than the storage
temperature. Freshly baked bread does not taste or feel like bread 24 hours
old. Bread can be stored so that it loses no moisture, yet readjustments in
the loaf take place, so that staling occurs. If bread is stored at temperatures
of 60C. or above, the texture remains more like that of freshly baked
bread and staling is not perceptible. But at this temperature bacterial
changes occur readily. If the bread has not lost considerable moisture, upon
reheating it, it acquires the characteristics of freshly baked bread.
The principle of Le Chatelier gives the factors of equilibrium: "Every
system in chemical equilibrium, under the influence of a change of any
single one of the factors of equilibrium, undergoes a transformation in
such direction that, if this transformation took place alone, it would pro-
duce a change in the opposite direction of the factor in question. The
factors of equilibrium are temperature, pressure and electromotive force,
corresponding to three forms of energy; heat, electricity and mechanical
energy."
Hydrogen-Ion Concentration
The symbol />H is very commonly used in present-day literature. Some
explanation of the term and its relation to hydrogen-ion concentration is
desirable. Perhaps it will be best to review briefly what is meant by hydro-
gen-ion concentration. In a solution of hydrochloric acid in water, the
molecule of the acid consists of an atom of hydrogen united to an atom of
chlorine. Hydrochloric acid molecules are found in the solution, but not all
the acid remains in the molecular form. Part of the acid molecules are
ionized into hydrogen ions and chlorine ions, the degree of ionization de-
pending upon the concentration, the more dilute the acid solution the
greater the percentage of hydrochloric acid ionized. The hydrogen ions are
positively charged, and the chlorine ions are negatively charged. In symbols,
the ionization of hydrochloric acid is expressed as follows:
HC1 =; H+ + Cl-
When a substance is ionized in solution the solution conducts an elec-
trical current.
When water is ionized it gives both hydrogen ions and hydroxyl ions.
Since the ionization of water is very slight, the amount of hydrogen and
hydroxyl ions in a liter of water is not great.
H 2 O < ; H+ + OH-
In pure water the concentration of hydrogen ions and hydroxyl ions is
HYDROGEN-ION CONCENTRATION 27
equal at 22 C. The reaction of water varies at various temperatures, so
that the following discussion is confined to room temperature or 22C. The
concentration of the hydrogen ions and hydroxyl ions is of a
10,000,000
gram-molecular weight (mole) each per liter. A normal solution of hydro-
gen ions contains 1 gram-molecular weight (1 gram) of hydrogen ions per
liter of solution; a normal solution of hydroxyl ions contains 1 gram-
molecular weight (17 grams) of hydroxyl ions per liter of solution. A liter
of pure water contains of a mole of hydrogen. This requires
10,000,000
many figures to express as a fraction, so for convenience the concentration
is expressed as follows : ^^ = 10~ 7 . Again for convenience Sorensen
JLU,UUU,UUU
proposed to disregard the minus sign and use the numerical value of the
exponent 10 to express the reaction corresponding to the concentration of
hydrogen ions.
When the concentration of the hydroxyl ions is equal to that of the
hydrogen ions, the concentration of hydroxyl ions is also of a
10,000,000
mole or 10~ 7 . This is the neutral point. The term />H is used to denote the
concentration of the hydrogen ions only. Sometimes />OH is used to denote
the concentration of the hydroxyl ions. Thus when the concentration of the
hydrogen ions is pH 7, that of the hydroxyl ions is pOH 7. If the con-
centration of the hydroxyl ions is multiplied by the concentration of the
hydrogen ions a definite product is obtained. In fractions this would be
written thus:
i i i
10,000,000 10,000,000 100,000,000,000,000
But in the exponential notation it is expressed as follows:
10~ 7 X 10- 7 = 10~ 14
When the hydrogen-ion concentration in a solution is increased, the hy-
droxyl-ion concentration is decreased, so that the product of the concentra-
tion of the hydrogen and hydroxyl ions always gives 10~ 14 , and this is a
constant for the product of these two ions. Thus in a solution that has a
pH 6 the hydrogen ions exceed the hydroxyl ions but the product of their
concentrations is the constant 10~ 14 . In a solution that has a />H 6 the
concentration of the hydrogen ions expressed in fractions is ^ r ^ of
1,000,000
a mole of hydrogen. In the same solution the concentration of the hy-
droxyl ions is of a mole. The product of these two concentra-
1 OU , 000 ,OOvJ
28 RELATION OF COOKERY TO COLLOID CHEMISTRY
tions gives the constant. Expressed in exponential notation it is 10 6 )x
10 8 = 10~ 14 . In a solution that has a pH 8 the hydroxyl ions exceed the
hydrogen ions but the product of their concentration is again 10~ 14 . When
the concentration of the hydrogen ions is /H 3 or 10~ 3 then the concentra-
tion of the hydroxyl ions is 10~ n and their product is again 10~ 14 .
Literally, the term pH means to a power. It is used to express the re-
action of a fluid, that is, its degree of acidity or alkalinity, but it does not
do this directly, as is shown in the above equations. It is an inverse logarith-
mic function, deprived of its minus sign. Experimentally it is determined
electrometrically and is really a number obtained from determining the
electromotive force (E.M.F. ) of a substance in a suitable apparatus and
by using this value of (E.M.F.) in a formula, computing the />H.
Hydrogen-ion concentration refers to the concentration of the ionized or
active ions per liter of substance. The />H value does not represent this
directly but for all practical purposes may be taken as a value represent-
ing it.
The relation of hydrogen-ion concentration and pH values in solutions
of varying normalities is given below.
TABLE 3
Solution
Grains of hydrogen
ion per liter
pH value
Normal
1.0
AV10
0.1
1
N/ 100
0.01
2
Ayiooo
0.001
3
tf/10,000
0.0001
4
N/ 100, 000
0.00001
5
Nf 1,000, 000
0.000001
6
N/ 10, 000, 000
0.0000001
7
The above arrangement shows that the pH value is riot an arithmetical
series or ratio but varies according to the logarithmic notation. Thus />H 2
is not one-half of pH 1 but one-tenth of it.
The number of times the hydrogen-ion and hydroxyl-ion concentrations
of a solution exceed that of pure water may be shown as follows. The
arrangement is by Alexander.
The />H values are determined by two methods: the principal one is by
electrometric determinations, the other is by the use of indicators. The
latter is a rapid and a very useful way to determine an approximate />H
value and to check apparatus. For an accurate determination the electro-
metric method must be used.
REFERENCES 29
TABLE 4
pH value
Number of times that the H- orOH-ion concentration exceeds
that of pure water
1
1,000,000
2
100,000
3
10,000
acid side
4
1,000
H-ion concentration
5
100
6
10
7
pure water, neutral
8
10
9
100
10
1,000
11
10,000
alkaline side
12
100,000
OH-ion concentration
13
1,000,000
LITERATURE CITED AND REFERENCES
Alexander, J. Colloid Chemistry. An Introduction with Some Practical Appli-
cations. Van Nostrand Co. (1924).
Alexander, J. Colloid Chemistry, Theoretical and Applied. By International
Contributors. Collected and edited by J. Alexander. Chemical Catalog Co.
(1926).
Bancroft, W. D. Applied Colloid Chemistry. McGraw-Hill Co., 3rd Ed. (1932).
Bancroft, W. D., and Rutzler, J. E., Jr. The Denaturation of Egg Albumin.
J. Physical Chem. 35: 144 (1931).
Bechhold, H. Colloids in Biology and Medicine. Translation by G. M. Bullowa.
Van Nostrand Co. (1919).
Bingham, E. C. Fluidity and Plasticity. McGraw-Hill Co. (1922).
Bingham, E. C. Viscous and Plastic Flow in Colloid Systems, p. 430. Colloidal
Behavior, edited by R. H. Bogue. McGraw-Hill Co. (1924).
Buchanan, R. E., and Fulmer, E. I. Physiology and Biochemistry of Bacteria.
Williams & Wilkins Co. (1928).
Burns, D. An Introduction to Biophysics. Second Edition. J. & A. Churchill
(1929).
Clayton, W. Foods as Colloid Systems. Food 4: 193 (1935).
Collins, W. D. Laboratory Thermometers. Ind. Eng. Chem. 13: 240 (1921).
Denton, M. C. What is Experimental Cookery? J. Home Econ. 11: 119 (1919).
Gortner, R. A. Outlines of Biochemistry. John Wiley & Sons (1929).
Gortner, R. A., and Doherty, E. H. Hydration Capacity of Gluten from Strong
and Weak Flours. J. Agri. Research 13: 389 (1913).
Fischer, M. H. Soaps and Proteins. John Wiley & Sons (1921).
Freundlich, H. The Elements of Colloidal Chemistry. Translation by G. Barger.
Methuen & Co. and E. P. Dutton & Co. (1924).
Freundlich, H. Colloid and Capillary Chemistry. Translation by H. S. Hatfield.
Methuen & Co. and E. P. Dutton & Co. (1926).
30 RELATION OF COOKERY TO COLLOID CHEMISTRY
Harkins, W. D. Surface Energy and Surface Tension, p. 192. Colloid Chemistry,
by J. Alexander. Chemical Catalog Co. (1926).
Holmes, H. N. Laboratory Manual of Colloid Chemistry. John Wiley & Sons
(1922).
Kopaczewski, W. Physics, Chemistry and Colloidal State, p. 547. Colloid Chem-
istry, by J. Alexander. Chemical Catalog Co. (1926).
Kruyt, H. R. Colloids. Translation, by H. S. van Klooster. John Wiley & Sons
(1927).
Langmuir, I. The Constitution and Fundamental Properties of Solids and Liquids.
II. Liquids. J. Am. Chem. Soc. 39: 1848 (1917).
Lloyd, D. J. The Problem of Gel Structure, p. 767. Colloid Chemistry, by
J. Alexander. Chemical Catalog Co. (1926).
Loeb, J. Proteins and the Theory of Colloidal Behavior. McGraw-Hill Co.
(1922).
Loeb, J. Crystalloidal and Colloidal Behavior of Proteins, p. 23. Colloidal Be-
havior, by R. H. Bogue. McGraw-Hill Co. (1922).
Mirsky, A. E., and Anson, M. L. Sulfhydryl and Bisulfide Groups of Proteins.
II. The Relation between Number of -SH- and -S-S- Groups and Quantity
of Insoluble Protein in Denaturation and in Reversed Denaturation. J. Gen.
Physiology 19: 427 (1936).
Mirsky, A. E., and Anson, M. L. Sulfhydryl and Bisulfide Groups of Proteins.
III. Sulfhydryl Groups of Native Proteins, Hemoglobin, and the Proteins of
the Crystalline Lens. J. Gen. Physiology 19: 439 (1936).
Mirsky, A. E., and Anson, M. L. The Reducing Groups of Proteins. J. Gen.
Physiology 19: 451 (1936).
Neurath, H., and Bull, H. B. The Benaturation and Hydration of Proteins.
I. J. Biol. Chem. 115: 519 (1936).
Ostwald, Wo. Theoretical and Applied Colloid Chemistry. Translation by
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Ostwald, Wo., Wolski, P., and Kuhn, A. Practical Colloid Chemistry. Trans-
lation by I. N. Kugelmass and T. Cleveland. Methuen & Co. London (1926).
Rahn, O. Why Cream and Egg White Whips. Explained on the Theory of Stable
Foams. Food Ind. 4: 300 (1932).
Robertson, T. B. The Physical Chemistry of the Proteins. Longmans Green &
Co. (1918).
Von Weimarn, P. P. Theory of the Colloid State of Matter, p. 27. Colloid Chem-
istry, by J. Alexander. Chemical Catalog Co. (1926).
Waidner, C. E., and Mueller, E. F. Note on Partial and Total Immersion Ther-
mometers. Ind. and Eng. Chem. 13: 237 (1921).
Zsigmondy, R. The Chemistry of Colloids. John Wiley & Sons (1917).
CHAPTER II
SUGAR COOKERY
Classification of the Carbohydrates
The carbohydrates are divided into three groups: the monosaccharids,
disaccharids, and polysaccharids. The monosaccharids are composed of one
saccharid or sugar group. They are sometimes called simple sugars. The
monosaccharids differ from each other in the number of carbon groups
and in the molecular arrangement. The monosaccharids contain alcohol
groups (HCOH), the number of which may vary from one to six.
In addition to the alcohol group a monosaccharid contains either an
aldehyde (HC O) or a ketone (C = O) group. Thus they are aldehyde
or ketone derivatives of complex alcohols and as such are called aldoses or
ketoses.
A biose is a sugar with two carbon groups, an alcohol group being at-
tached to one carbon and an aldehyde group to the other. A triose has
three carbon groups and has alcohol groups attached to two carbons and
either an aldehyde or ketone to the third carbon. The common monosac-
charids in foods are the hexoses, which contain six carbon groups. Five
of the carbons have alcohol groups, but the sixth has an aldehyde or ketone.
The common hexoses are dextrose and levulose, the former being an aldose,
and the latter a ketose. The following formulas though not conveying the
exact arrangement of the molecule illustrate the above points.
CH 2 OH CH 2 OH
CHOH CHOH
CHOH CHOH
CHOH CHOH
CHOH C = O
CHO CH 2 OH
Dextrose Levulose
All sugars higher than tetroses may assume two structural forms, the
pyran and the furan. The pyran form for a hexose sugar is a ring composed
of five carbons and one oxygen with one carbon outside the ring ; the furan
31
32
SUGAR COOKERY
form is a ring of four carbons and one oxygen with two carbons outside
the ring.
CH
\
CH 2 O
'CH C
Pyran
O
CH
H / H \ H
HO \ H HO / CH 2 OH
>H H
Beta-fructopyranose
O
HO.CH 2 /'
CH
-A
CH
\\
H HO
s OH
\|
1
CH 2 OH
Furan
OH H
Beta-fructofuranose
The two structural forms of the sugars are represented by the terms
glucopyranose and glucofuranose for glucose, fructopyranose and fructo-
furanose for fructose, etc. To avoid confusion of nomenclature, prefixes
are added to the terms indicating structural form to differentiate the
stereochemical forms (the same chemical and basic structural form but
with different spacial arrangements of the hydrogen and hydroxyl groups).
Thus the prefixes alpha-, beta-, gamma-, etc., added to the name of the
sugar with the ending denoting the structural form, such as alpha-gluco-
pyranose, beta-glucofuranose, definitely identify each sugar.
Haworth and his coworkers at Birmingham have worked out in detail
the way in which sugar units are united into chains. Haworth states that
there are several ways in which two glucose .units may be joined through
the intermediary of a common oxygen atom. But of the several OH posi-
tions available for providing the union of two glucose units, it has been
found that the union is formed through the first carbon of one unit and
the fourth carbon of the other glucose unit. Maltose is formed, as sho\vn,
by the union of two alpha-glucopyranose units. The union of about 30
alpha-glucopyranose units in this manner, according to Haw T orth forms
starch, though all investigators do not agree on the number of glucose
units in the starch chain. (See discussion of starch in Chapter XL)
Cellulose is composed of many beta-cellobiose units. In a manner similar
to that in which maltose is formed, two beta-glucopyranose units form
CLASSIFICATION OF THE CARBOHYDRATES
33
H OH H
The union of two a-glucopyranose units gives a-maltose
HO.CH 2
a-maltose
beta-cellobiose. Sucrose is composed of one alpha-glucopyranose united
through the first carbon to beta-fructopyranose.
The disaccharids contain two monosaccharid sugar groups; the poly-
saccharids contain many sugar groups. There are also trisaccharids. There
is always the possibility that the trisaccharids and some of the other rare
sugars may become commercially important, but at the present time they
are little used except in scientific work.
The common disaccharids found in foods are sucrose, maltose, and lac-
tose. Sucrose is composed of one dextrose and one levulose group; maltose
is made up of two dextrose groups ; and lactose is composed of one dextrose
and one galactose group.
Following is a list of the common carbohydrates used in foods. For a
complete list a physiological or organic chemistry may be consulted.
MONOSACCHARIDS :
Dextrose or glucose
Levulose or fructose
DISACCHARIDS
Sucrose
Maltose
Lactose
POLYSACCHARIDS
Dextrins
Starch
Cellulose
Pectins
Gums
34 SUGAR COOKERY
Sources of the Common Sugars
Dextrose or glucose, for it is known by both names, is widely distributed
in fruits, honey, and some vegetables. The sugar known by the trade name
"Cerelose" is practically a pure crystalline dextrose and is made from corn.
The term dextrose or glucose should be applied to crystalline dextrose
or its solution. Commercial corn sirup has been incorrectly called glucose.
It is made from corn, the starch being hydrolyzed with acid. Hydrolysis
is carried to the point at which 40 to 50 per cent of the starch is changed
to sugar, the remainder being split into dextrins. The sirup contains both
dextrose and maltose, but for convenience the sugar is usually all deter-
mined and expressed as dextrose. Thus corn sirup is a mixture of dextrin,
maltose, dextrose, and water.
Levulose or fructose is also widely distributed in natural foods, often
accompanying dextrose, or dextrose and sucrose. At present, pure crystalline
levulose is expensive. Honey contains nearly equal parts of dextrose and
levulose. When honey crystallizes, the greater part of the levulose is in
the sirup and the dextrose in the crystals.
Sucrose is widely distributed in plants, often with dextrose and levulose.
The common sources of it commercially are the sugar beet, the sugar cane,
the sugar maple, and the sugar palm. It is the common granulated sugar
on the market and is practically pure whether obtained from the beet or
cane. Maple sugar is not purified, for it would then lose the flavor for
which we prize it.
Maltose is formed as an intermediate product when starch is hydrolyzed
by boiling with mineral acid in the manufacture of commercial corn sirup
from corn. Commercially it is prepared from starch by a diastatic enzyme
and it is also found in germinating cereals and malt products.
Lactose is obtained from milk. One of its uses is for infant feeding.
Relative Sweetness of the Sugars
Sweetness is a quality that is detected by taste, but there is no exact
test for it. Much depends upon how the test is conducted, whether the
tongue is dry or moist, upon what part of the tongue the sample is placed,
and with several other conditions, the fatigue of the sense of taste. Some
persons detect sweetness in less concentrations than others. It cannot be
expected that all people will agree in their estimates of the relative sweet-
ness of the sugars, even with carefully worked out tests.
In rating the sweetness of the various sugars it is a commonly accepted
practise to rate sucrose as 100. Sugars sweeter than sucrose are ranked
higher than 100, and those less sweet are ranked lower.
Biester and Wood of the University of Minnesota give the following
rating to sugars :
EFFECT OF ACID UPON SUGARS 35
Levulose 173.3
Sucrose 100.0
Dextrose 74.3
Maltose 32.5
Lactose 16.0
Sale and Skinner of the Bureau of Chemistry (Water and Beverage
Laboratory) rate the sugars as follows:
Sucrose 100
Dextrose 50
Levulose 150
Maltose 50
Invert sugar 85
Paul in comparing the sweetness of several sugars with sucrose gives
the following value :
Sucrose 100
Dextrose 52
Levulose 103
Lactose 28
A commonly accepted value of dextrose at the present time is about
70 to 75. There is the probability that this is too high and that 50 is a
better figure. Levulose is conceded by all to be sweeter than sucrose, but
again there is no agreement as to how much sweeter. Some authorities rank
it 120 to 125. With the higher figures for the sweetening powers of dex-
trose and levulose it would seem that invert sugar should be sweeter than
the original sucrose. But the manufacturers of carbonated beverages, to
whom this would be beneficial, since they use solutions of sirup, do not
think that invert sugar is any sweeter than sucrose, even though 342 units
of sucrose yield 360 units of invert sugar or a gain of 5 per cent in weight.
Effect of Acid upon Sugars and Hydrolysis o Sugars
Strong concentrated acids decompose all the sugars producing humus or
caramel substances. The weak acids, malic and citric in fruits, lactic in sour
milk, acetic acid, and salts with an acid reaction like cream of tartar, affect,
the sugars in different degrees, depending on the particular acid used, the
strength of the acid, whether it is heated, and the length of time of heating.
The monosaccharids, dextrose and levulose, are not affected to any ap-
preciable extent by weak acids. When sucrose is cooked with weak acids
it is partially hydrolyzed to dextrose and levulose, but since the invert
sugars are not affected by the acid practically no other change takes place.
Lactose is only very slowly hydrolyzed by acid to dextrose and galactose.
Maltose is less readily affected by acid than sucrose, but is slowly hy-
drolyzed to two molecules of dextrose.
Sucrose and fondant. Sucrose is very easily hydrolyzed, even by very
36 SUGAR COOKERY
weak acids, though the addition of water to the sugar molecule cannot
he brought about by mixing sugar and water, but may be brought about
by enzymes as well as acids. The weak acids used in cookery lemon juice,
vinegar, fruit juices, or the acid salt cream of tartar all cause sucrose to
combine with water forming dextrose and levulose. Hydrolysis takes place
more rapidly if the solution is heated. In making fondant with cream of
tartar, if the sirup is boiled slowly for a long time, more inversion may
take place than when the sirup is boiled quickly with a larger amount of
cream of tartar. Compare the length of time required to bring about
crystallization in Experiments 7C, 1, and 7C, 2. Hydrolysis of fondant
containing cream of tartar occurs during storage though the rate is slow
at the storage temperature. Fondant made with cream of tartar and stored
in a fairly tight container becomes softer than fondant of the same con-
sistency before storage, but without the addition of cream of tartar. The
amount of the acid salt to bring about this softening at room tempera-
ture imparts a slightly sour taste to the fondant. To many persons this
slight acidity improves the flavor. In fondant made with a larger amount of
cream of tartar (Experiment 7C, 4), considerable hydrolysis may occur
with short storage.
To determine the effect of salts found in hard water upon the decom-
position of dextrose in fondant, some fondants were made Avith 10 per
cent of dextrose added to sucrose and distilled water. To the solution
different salts similar to those found in water were added, the fondants
made and stored in a heavy glass container, with a tight-fitting lid. They
were kept for two years. Acid calcium phosphate was added to some of the
fondant to compare an acid-reacting salt containing calcium with the other
calcium salts used. At the end of one year the fondants made with calcium
acid phosphate were plastic and kneadable, whereas those made with mag-
nesium sulfate, calcium sulfate, and other salts, as well as the control with
no salt, were too hard and dry to be kneaded. Here slow hydrolysis from
the calcium acid phosphate probably occurred over a long period, but drying
out of the fondant was also prevented, which was due to the hygroscopic
property of the levulose. If fondant is to be stored for some time before
it is molded the fondant made with an acid salt remains soft and plastic, or
Keeps better than fondant made without an acid or acid salt.
Hydrolysis of sucrose is often spoken of as inversion and the resulting
sugar as invert sugar. The reason for this name is found in the effect of
invert sugar upon a beam of light. If a straight beam of light is allowed
to pass through a solution of sucrose in an instrument called a polariscope,
the beam of light is rotated to the right and the sucrose is called dextro-
rotary. After the sucrose is hydrolyzed, the ray of light is rotated to the
left and the invert sugar is levo-rotary. Because of this inversion of a beam
of light, hydrolyzed sucrose is called invert sugar. Dextrose is dextro-
rotary and sucrose is levo-rotary. It is due to the fact that levulose rotates
EFFECT OF ALKALIES UPON SUGARS 37
the beam of light further to the left than dextrose rotates it to the right
that the rotation of invert sugar is opposite to that of sucrose.
Hydrolysis of sugars by enzymes. Enzymes also bring about hy-
drolysis of the disaccharid sugars. Since heat destroys enzymes the reaction
must occur at a low temperature. The enzyme invertase causes hydrolysis
of sucrose to dextrose and levulose. Maltose is prepared from corn by using
an enzyme.
Hydrolysis in chocolate creams. Jordan states that the liquefied
centers of chocolate creams and other confections are brought about by
acids, acid salts, or enzymes. The substance bringing about the hydrolysis is
added when the fondant is fairly hard and the softening due to the hydrol-
ysis occurs during storage. Paine states that the amount of the acid or acid
salt required to bring about inversion imparts a perceptible acid taste to
the fondant. Evaporation of liquid from the fondant must be prevented,
or the fondant loses water and becomes dry. Then some moisture is neces-
sary for hydrolysis to occur. The enzyme, invertase, may be added when
the fondant is beaten or when it is molded before dipping. The proper
amount of invertase is added for the inversion of the fondant, and accord-
ing to Paine this inversion takes place more readily at />H 4.4 to 4.6. To
give this acidity citric acid is added in small quantities. Invertase may be
used in fondant for chocolate creams, in confections with fruit like cherries
and pineapple, and in bonbons. The fat of chocolate prevents the confec-
tions dipped in it from losing moisture by evaporation. The bonbons dry
out more rapidly than the chocolate-covered candies. Paine states that the
addition of a small amount of egg albumen or egg white lessens evaporation
from the fondant.
Hydrolysis of starch. Starch, like sucrose, is very readily hydrolyzed
by acids, and the reaction takes place more rapidly at a high temperature.
When starch is used with acid fruit juices, a larger proportion of starch is
required to thicken the mixture to a definite consistency than is needed for
an equal quantity of water or milk. Fillings for lemon or cherry pie, because
of the hydrolysis by acid during cooking, need a larger proportion of starch
for thickening than fillings like chocolate cream.
Effect of Alkalies Upon Sugars
Strong alkalies, like strong acids, decompose the sugars. Weak alkalies
or salts with alkaline reaction, like sodium bicarbonate, common baking
soda, also act upon the sugars. Even alkaline salts found in hard water
may produce considerable decomposition in some of the sugars. Of the
disaccharids those most easily affected by acids are least readily decomposed
by alkali, and vice versa. Sucrose is scarcely acted upon by a weak alkali,
but maltose and lactose are affected more readily.
The monosaccharids are easily decomposed by alkalies, even very weak
ones. If the sugar is allowed to stand in a solution with a weak alkali
38 SUGAR COOKERY
many substances may be formed. Decomposition is brought about so rapidly
with strong alkalies that not so many products are formed with it. Nef
states that, of the 116 possible decomposition products with dextrose and
a weak alkali, 93 have been isolated. Very weak alkalies may cause re-
arrangement of the molecule. In the manufacture of dextrose great care
must be taken to keep the reaction acid to prevent an off color and taste.
The action of an alkali upon dextrose produces first a yellow tinge which
becomes deeper and finally brown if carried far enough. This decomposi-
tion is called caramelization. With very slight caramelization of dextrose
the flavor may not be very noticeable, but it may become strong and bitter,
and characterized by a strong, pungent, acrid after-taste. In sections of the
country where the water is very hard, enough decomposition to affect the
flavor may be brought about in ordinary cooking. This is more noticeable
when the sugar is cooked slowly. The addition of a little lemon juice,
vinegar, or the acid salt, cream of tartar, will prevent the discoloration and
the change in flavor. In some instances this browning or caramelization is
an advantage. For example, baked beans brown better when dextrose is
added than when sucrose is used.
Levulose, like dextrose, is unstable in an alkaline solution, decomposing
as readily or more so than dextrose and giving many decomposition prod-
ucts. But in cookery its decomposition by alkalies can be prevented in the
same way as that of dextrose. Candy made from honey often has a strong
flavor that may be rather disagreeable, owing to decomposition of the
dextrose and levulose during cooking. If just enough acid is added to com-
bine with the alkali present, the characteristic flavor of honey is retained.
Moisture-Absorbing Power of the Sugars
All sugars should be stored in a dry place for they deteriorate if stored
where it is damp. This power of absorbing moisture can be made use of
to improve some foods, but it is a detriment in others.
Browne reports that the sugars having the highest absorptive power from
a saturated atmosphere are the levulose-containing substances : invert sugar,
honey, levulose, and molasses. He finds that the percentage of water ab-
sorbed has no relation to the percentage of levulose present. This would
suggest that cakes made with levulose-containing products would not dry
out so rapidly as cakes made with sucrose. In practise, this is found to be
true. Cakes made with part levulose or levulose-containing substances do not
dry out so rapidly as those made with sucrose.
Honey and molasses are used in many family recipes for cookies, par-
ticularly the kinds made for holidays, for they can be made a long time in
advance of their intended use and they remain moist with storage in many
instances the moisture content seems to increase during storage.
Invert sugar either added to food or formed by inversion during cooking
is found in many food products. In the bakery trade it is used to prevent
SOLUTIONS 39
drying and checking. The acid in fruits inverts sucrose. The amount of
total sugar that can be held in solution in a given quantity of liquid is
greater if it contains a mixture of sucrose, levulose, and dextrose. Rich
preserves made of fruit containing little acid do not crystallize so readily
during storage if lemon juice is added when they are being made. The
lemon juice brings about more inversion than the less acid fruit juice. The
invert sugar does not crystallize so readily as the sucrose, the total quantity
of sugar held in solution is greater, and there is less evaporation.
The levulose-containing substances should be avoided for hard candies.
Duryea states that maltose is better to use in hard candies than dextrose,
because the candies remain drier. He also adds that another advantage
of using maltose in hard candy is that maltose is not so readily affected
by alkali. The decomposition caused by use of dextrose and alkaline water
is avoided.
The Melting Point of the Sugars and the Effect of Heat
When sugars are heated without the addition of water a point is reached
at which they change from a crystalline to a liquid state. This is called
the melting point.
Mackenzie states that the melting point of sucrose is 160 to 161 C.
Impure solutions of sucrose will give variable melting points. After sugar
is melted and cooled slowly it forms the hard amorphous sugar sometime?
called "barley sugar." The amorphous form of sugar like the amorphous
sulfur slowly reverts to the crystalline form. If sucrose is heated above the
melting point brownish-colored substances called caramel are formed. In
the presence of moisture, caramelization may begin at temperatures below
100C. Caramel is composed of a number of substances, decomposition
products of sucrose with loss of water.
Maltose melts at about 100C. Having a lower melting point than
sucrose it decomposes more easily by heat.
Dextrose crystallizes as the hydrate, C 6 Hi2O 6 .H 2 O, that is, one mole-
cule of water is combined with the molecule of dextrose. When heated
slowly it loses this water of crystallization between 50 and 60C. Perkin
and Kipping state that the melting point of the hydrate is 86, and that of
the anhydrous form is 146C.
The melting point of levulose is 95 C.
Solutions
Sugar and other substances are used constantly in cookery processes.
Therefore, it is desirable to know something about the properties of solu-
tions.
A solution is composed of two parts: one, the solute, is the dissolved
substance; and the other, the solvent, is the substance in which the solute
40 SUGAR COOKERY
is dissolved. A solution is a homogeneous mixture. This means that it is
uniformly mixed or alike in all parts.
A solution may be a gas dissolved in a solid, a gas in metal; a gas in a
liquid, air in water; a liquid in a liquid, alcohol in water; or a solid in
a liquid, sugar in water. It is to the class of solids in liquids that many
of our solutions in cookery belong.
Solubility of Substances in Solution
Solubility means the amount of a specific substance that will dissolve
in a given volume of a specified solvent. If the solvent is not mentioned
it is understood to be water. Solubility is generally expressed as the number
of grams of solute that will dissolve in 100 cc. of solvent, and as the tem-
perature affects solubility it is usually mentioned. If the temperature is not
stated it is understood to be room temperature or 20 to 22C.
Factors determining the solubility. Temperature, the fineness of
division and the nature of the solute, and the nature of the solvent deter-
mine the solubility to a great extent. Some substances are highly, others
only slightly, soluble in water, and still others are highly insoluble in this
solvent. Some substances will dissolve best in alcohol, or chloroform, or
ether, or benzine. Some liquids, like alcohol and water, will dissolve in all
proportions, but there is a limit to the solubility of all substances of a
crystalline form.
Fineness of division of the solute. A larger amount of the crystal-
line solute is soluble if it is very finely divided or powdered than if left
in large crystals. This does not refer to the ease or quickness of solution
but to the total number of grams dissolved in 100 cc. of the solvent. This
increase in solubility is due to the increased surface energy of the smaller
particles in the solvent. The diameter of the particles must be less than I/A
to increase the solubility to any great extent.
Temperature. The solubility of most crystalline substances in water
is increased by heating, though some are little affected by temperature
change, and a few are less soluble in hot water than in cold. Sodium
chloride, common salt, is an example of a substance that is little affected
by temperature change. At 0C. about 35.6 grams will dissolve in 100 cc.
of water, and about 39 grams at 100. Calcium hydroxide is only half as
soluble at 100 as at 20. The solubility of the sugars is increased by
elevation of temperature. At 0C., 179 grams of sucrose will dissolve; at
100C. 487 grams will dissolve.
Addition of other substances. Two forms of the same compound
may give different solubilities. Thus anhydrous lactose (without water of
crystallization) has one solubility and the hydrated form has another. Some-
times the addition of another substance, organic or inorganic, to the solu-
tion will increase or decrease the solubility of the solute. If, after all the
sucrose possible is dissolved, some potassium acetate, sodium chloride, or
SUCROSE 41
many other salts, is added to the solution, more sucrose can be dissolved.
This may affect the solubility of sugar in candy making, for it is known
that different waters, with different proportions and kinds of minerals, do
not always give identical results, with the same sugar, for the same kind
of candy.
Saturated solutions. Once all the solute is dissolved that can possi-
bly be held by a definite amount of solvent at a constant temperature, any
excess of the solute remains unchanged. The saturated solution is one that
contains all the dissolved solute that it can take up when in contact with
undissolved solute. In other words, it is a solution which when placed
with excess of the solute at a definite temperature is in equilibrium, i.e.,
there is neither increase nor decrease in concentration of the solute.
Supersaturated solutions. One should not define a saturated solution
as one containing all the solute it can hold, for a supersaturated solution
holds more than a saturated one. If water is heated to 70C. and all the
sucrose added that can be dissolved by the water at this temperature, one
has a saturated solution. There should be no excess of the solid left with
the liquid. If this solution is carefully cooled to 40C. without stirring
more sucrose will .be in solution than could have been if the water had not
been heated above 40. The cooling of a saturated solution leads to the
formation of crystals, and any excess beyond saturation is gradually pre-
cipitated as the temperature drops, though crystallization may not begin
immediately. But some substances, like the sugars, require longer than
others for crystallization to commence, unless the solution is stirred or
agitated.
The Solubility of the Sugars
The solubility of the sugars determines their use to a certain extent. It
is obvious to one who does a great deal of cooking that a sugar that requires
6 pounds of water to dissolve 1 pound of sugar, could not be used for con-
centrated sugar products like jellies, jams, frostings, or even cakes.
Sucrose. Sucrose has the greatest solubility of the disaccharid sugars.
Browne in his "Handbook of Sugar Analysis" states that, at 20C., 204
grams are soluble in 100 cc. of water. Thus at room temperature about
2 grams of sucrose are soluble in 1 cc. of water. At 100C. 487 grams of
sucrose are soluble in 100 cc. of water. For solubilities at other tempera-
tures see Table 5.
In Table 5 the solubility of sucrose is expressed in two ways. In column
2 is given the amount of sucrose dissolved in water to make 100 grams
of solution. Thus at 0C., 64.18 grams of sucrose are dissolved in 35.82
grams of water to give a total of 100 grams of solution. The third column
states the number of grams of sucrose dissolved in 100 grams of water at a
definite temperature.
42 SUGAR COOKERY
TABLE 5
SOLUBILITY OF SUCROSE IN WATER AT DIFFERENT TEMPERATURES
(From Browne's "Handbook of Sugar Analysis"}
Temperature,
degrees C.
Grams of sucrose
in 100 grams of
solution, or
per cent
Grams of sucrose
dissolved by 100
grams of water
Specific gravity
of solution
64.18
179.2
1.31490
5
64.87
184.7
1.31920
10
65.58
190.5
1.32353
15
66.30
197.0
1.32804
20
67.09
203.9
1.33272
25
67.89
211.4
1.33768
30
68.70
219.5
1.34273
35
69.55
228.4
1.34805
40
70.42
238.1
1.35353
45
71.32
248.7
1.35923
50
72.25
260.4
1.36515
55
73.20
273.1
1.37124
60
74.18
287.3
1.37755
65
75.18
302.9
1.38404
70
76.22
320.5
1 . 39083
75
77.27
339.9
1.39772
80
78.36
362 . 1
1.40493
85
79.46
386.8
1.41225
90
80.61
415.7
1.41996
95
81.77
448.6
1.42778
100
82.87
487.2
1.43594
Percentage of Sucrose in Saturated Solutions. From Table 5
the percentage of sugar may be obtained. At 0C., 64.18 grams of sugar and
35.82 grams of water give 100 grams of solution, so that the number of
grams of sugar may be read as percentage of sucrose or 64.18 per cent.
Maltose. Maltose is not a common sugar on the market. When used
to make jelly, it crystallizes from the jelly, like dextrose. Gillis has re-
ported the following solubility.
Lactose. The use of lactose in the home is limited because it is not very
soluble and lacks sweetness. According to Greenleaf, if lactose is crystal-
lized below 93.5C. the alpha hydrate form is obtained. Above 93.5C. the
beta lactose is formed. Beta lactose is about one-fourth sweeter than
alpha hydrate and dissolves more rapidly, hence does not leave a sandy
sensation in the mouth. Hudson states that at the final solubility of lactose
there are 1J^ parts of the anhydrous to 1 of the hydrate. Hunziker and
LACTOSE
43
TABLE 6
SOLUBILITY OF MALTOSE IN WATER (Gillis)
Temperature,
degrees C.
Grams of maltose in 100
grams of solution, or
per cent
Grams of maltose dissolved
by 100 grams of water
0.6
36.1
56.5
21.0
44.1
78.9
29.6
48.0
93.2
34.4
49.6
98.4
43.5
55.3
123.9
49.4
58.3
139.8
54.2
60.2
151.4
59.8
63.7
175.2
66.3
66.7
200.0
74.2
72.3
261.5
87.0
79.3
383.8
96.5
85.1
569.3
Nissen state that its solution is complete after shaking it 170 hours at
constant temperature. Herrington found that the addition of calcium
chloride to a lactose solution increased the solubility of lactose from 28.6
to 29.5 grams per 100 grams of water at 32C. An analysis of the pre-
cipitate showed the crystals to be a compourd of lactose with calcium
chloride. The following table of solubility of lactose is from Hudson.
TABLE 7
SOLUBILITY OF LACTOSE IN WATER (Hudson)
Temperature,
degrees C.
Final Solubility
Grams of lactose per 100
grams of solution, or
per cent
Grams of lactose dissolved
by 100 grams of water
10.6
11.9
15
14.5
16.9
25
17.8
21.6
39
24.0
31.5
49
29.8
42.4
64
39.7
65.8
74
46.3
86.2
89
58.2
139.2
44
SUGAR COOKERY
Dextrose. Dextrose and levulose are the only monosaccharid sugars
used in cookery to any extent. Dextrose has in recent years been put on the
market in crystalline form under the trade name of "Cerelose." Combs and
Bele give the solubility of "Cerelose" as shown in Table 8.
TABLE 8
SOLUBILITY OF "CERELOSE" IN WATER (Combs and Bele}
Temperature,
degrees C.
Grams of "Cerelose" per
100 grams of solution, or
per cent
Grams of "Cerelose" dis-
solved by 100 grams of
water
20
63
49.7
73.7
83.1
281.1
Thus at room temperature about 1 part of "Cerelose" is soluble in 1
part of water. "Cerelose" is less soluble than sucrose and goes into solution
at a slower rate.
The solubility of dextrose limits its use in cookery to a certain extent.
Jellies average about 60 to 70 parts of sugar by weight and 30 to 40
parts of liquid or juice. Dextrose at room temperature is soluble in water
to the extent of 1 part of dextrose to 1 part of water. Since the finished
jellies average over 50 per cent of sugar, when dextrose alone is used
in jelly it soon begins to crystallize after the jelly is cooled. If the jelly is
not covered it crystallizes very rapidly.
Levulose. Levulose is very soluble. It has a greater solubility than
sucrose. Since it is very soluble it must be present in very large quantities
before it crystallizes and is therefore very hard to crystallize. The data in
the table for the solubility of levulose are obtained from the results of
Jackson, Silsbee and Proffitt. The data in the third column are computed
from the grams of levulose soluble in 100 grams of solution.
Properties of Solutions
A solute dissolved in a solvent affects the properties of the solvent or in
other w r ords alters certain of its constant characteristics. No discussion of
osmotic pressure is given ; the effect on the freezing point is discussed in
the chapter on freezing. These characteristics may be listed as follows:
a. The vapor tension is lowered.
b. The boiling point is elevated.
c. The freezing point is lowered.
d. The osmotic pressure is increased.
EFFECT OF THE SOLUTE ON VAPOR TENSION 45
Vapor tension. Vapor tension may be defined as the vapor or gaseous
pressure of a liquid. The vapor tension of a liquid depends upon the amount
of vapor formed. Some liquids, like alcohol, evaporate rapidly and have a
high vapor tension. Others, like water, evaporate more slowly. This gaseous
pressure soon reaches a maximum at any given temperature. The maximum
pressure at a definite temperature represents the vapor tension of the liquid.
TABLE 9
SOLUBILITY OF LEVULOSE (Jackson, Silsbee and Proffitt)
Temperature,
degrees C.
Grams of levulose in 100
grams of solution, or
per cent
Grams of levulose dissolved
by 100 grams of water
20
78.94
374.8
25
80.29
407.3
30
81.64
444.6
35
82.98
487.5
40
84.34
538.5
45
85.64
596.3
50
86.90
663.3-
55
88.10
740.3
Effect of the solute on vapor tension. When a substance is dis-
solved in a liquid the vapor tension of the solvent is lowered, i.e., there is
less tendency to pass into the vapor state, hence the gaseous pressure is
decreased.
If water is the solvent, there is a tendency with a high concentration of
some substances for vapor from the air to enter the solution, thus increas-
ing the quantity of the solvent. This is particularly true of sugar solutions,
when the humidity of the air is high and the solutions are concentrated.
On damp, rainy days, fondant and similar candies have to be beaten for
a longer time to crystallize, unless they are cooked to a little higher tem-
perature so as to obtain a greater concentration.
The fact that it is harder for the vapor to leave the surface of the liquid
when there is a soluble substance in it is made use of in the following or
similar ways to keep food moist. A covered vessel containing food loses
moisture from the food until the air space is saturated with vapor. If the
vessel is tight enough, the food does not dry out to an appreciable extent.
If two dishes are placed in an enclosed vessel, one of them containing
water and the other a heavy sugar solution, the sugar solution, since it
loses vapor with difficulty and absorbs liquid, will gradually absorb water
from the other dish. If two foods are placed in the same container, the
one with more sugar will gradually absorb moisture from the other. This
is why an apple is often put in a box with a fruit cake, the apple drying
46 SUGAR COOKERY
up and keeping the cake moist. Cake and bread should not be stored to-
gether, as the bread will become dry quickly.
The Boiling Point of Water and Solutions
Water standing in an open vessel gradually evaporates, so that eventually
all the water disappears in the form of vapor. We know that evaporation
takes place more rapidly on warm days than on cool ones, and more rapidly
from a wide shallow vessel than from a narrow deep one. As the tempera-
ture is increased, the rapidity of the motion of the molecules is increased.
Therefore a larger number escape from the liquid as the temperature
increases, most of them being carried away by air currents.
Saturated vapor. If we cover a vessel of water, leaving an air space
between the surface of the liquid and the cover, evaporation takes place
for a time just as from an uncovered vessel. But when the vapor cannot be
carried away, the air above the liquid soon becomes filled \vith vapor mole-
cules. Of course some of them reenter the liquid. When they are entering
the surface of the liquid as rapidly as they are leaving it, the air is said to be
saturated and is in equilibrium with the liquid, i.e., the saturation point
is reached when the air holds all the vapor possible at that temperature.
If the temperature is increased the velocity of the molecules is increased,
and they leave the surface of the liquid faster than they enter until equi-
librium is again established. If the temperature is reduced, a part of the
vapor condenses into the liquid and forms drops of liquid on the sides and
cover of the vessel or on the surface of the liquid.
The boiling point. When water is heated slowly enough, air bubbles
are noticed forming on the sides and bottom of the pan. They come from
the air that has been held in solution by the water. A similar thing may
be noticed on a warm day when a glass or pitcher of cool water is left in
a warm room. The air bubbles collect on the sides of the glass or pitcher,
and if the vessel is jarred many of them will rise to the top of the water
and break. If heating of the water is continued the vapor begins to form.
Many of the first vapor bubbles collapse before they reach the surface.
Since the heat is applied at the bottom of the pan the vapor forms at
the bottom of the liquid. With the increased speed of the molecules, due
to the increased temperature, greater pressure is obtained, so that the
formation of vapor is more rapid until a point is reached at which the
rate of loss of heat from the water in the escaping vapor is equal to the
heat received by the liquid. If the rate at which the heat is applied is con-
stant, the bubbles are uniform in size. If a thermometer is held in the liquid
it is found that when this point is reached the temperature is constant.
This is the boiling point. A child might say that when a liquid is bubbling
it is boiling, and it would be a fairly good definition. However, the chemist
or physicist would word his definition differently. With vapor formation,
pressure is exerted. Since the bubble is less dense than the liquid it comes
ELEVATION OF THE BOILING POINT 47
to the surface. But the bubble cannot reach the surface until the pressure
within it is just a little greater than the pressure of the liquid on the
bubble. The pressure on the bubble in an open pan comes from the weight
of the column of liquid above it and the atmospheric pressure on the
surface of the liquid. Another way to define the boiling point is to say that
it is the temperature at which the pressure of the saturated vapor within
the liquid is just greater than the outside pressure on the surface of the
liquid.
If you live at sea level the boiling point of water is 100C. The Bureau
of Standards defines the boiling point of water as the point at which
ebullition is violent. Slow-bubbling water does not register quite as high
a temperature as rapidly bubbling water, but in cooking food in water
there is no great advantage in having the water boiling violently. The food
will cook nearly as rapidly in the slower bubbling water. With gas or
electricity it is an economy of fuel to lower the heat when the water begins
to boil, unless it is desirable to evaporate the liquid quickly.
The conversion of water from a liquid to a gaseous state requires a
certain amount of energy. This energy is expressed in terms of heat. To
change a gram of water at 100C. to vapor at 100 requires about 540
calories of heat. If the heat applied to boiling water is increased, the
quantity of water changed to vapor in a given time is increased. The vapor
escapes from the surface of the liquid, but in a pan the free surface is
limited. However, in boiling water it escapes from the free surface and
from the surface of the bubbles. The temperature of the water cannot be
increased because the heat lost by evaporation is equal to the heat received.
If the heat is increased, the heat lost by evaporation is increased and the
surface of the bubbles is increased enormously beyond the free surface of
the liquid to aid evaporation.
Lowering the boiling point. The boiling point of a liquid may be
lowered by reducing the pressure on the liquid. This may be done by
boiling the liquid in a partial vacuum. The boiling point is also lowered
with increased elevation above sea level. The atmospheric pressure is not
so great at high altitudes because of the lessened column or depth of air.
For each 960 feet above sea level the boiling point is decreased 1C.
Elevation of the boiling point. The boiling point of a liquid can
be elevated by increasing the pressure upon it. This may be done by pre-
venting the vapor above the liquid from escaping. If a soluble substance
is added to a liquid the resulting solution has a higher boiling point than
the pure liquid.
The pressure of a gas increases as the temperature increases. When
vapor is confined, as in a pressure cooker, the boiling point of a liquid
in the cooker is elevated. As the temperature is increased, the pressure
of the confined vapor on the surface of the liquid is increased. Therefore
a higher temperature is required to form great enough pressure in the
vapor bubbles within the liquid for them to reach the surface of the liquid.
48 SUGAR COOKERY
Thus the boiling point is elevated. The higher the temperature of the
confined vapor the greater the pressure on the liquid. The greater the
pressure on the liquid the higher the boiling point.
The boiling point of solutions. Each gram-molecular weight (mole)
of a non-ionized substance in a liter of water elevates the boiling point
0.52C. A gram-molecular weight of a substance is its atomic or com-
bined atomic weights. For example, sucrose is composed of carbon, hydro-
gen, and oxygen with the formula Ci2H 2 2On. The atomic weight of
carbon is 12; that of hydrogen is 1; of oxygen, 16. Thus 12 carbons, 22
hydrogens, and 11 oxygens give a molecular weight of 342 grams. The
boiling point of a liter of water containing 342 grams of sucrose is elevated
0.52C. Two moles of sucrose would elevate the boiling point 1.04C.
The boiling point can be elevated as long as the substance added is soluble.
When the solution becomes saturated, or the point is reached at which no
more can be dissolved, the boiling point is constant for substances that
behave normally in solution. If boiling is continued so that the solvent
is vaporized, the excess solute beyond saturation is crystallized. This is
illustrated in Experiment 3 in the laboratory outline.
Effect of ionized substances on the boiling point. Some sub-
stances when dissolved in water are ionized. In a solution of sodium
chloride, for example, not only sodium chloride molecules are found but
also sodium ions and chlorine ions.
NaCl ^H I Na+ + Cl~
The atomic weight of sodium is 23 and that of chlorine is 35. If 58
grams of sodium chloride (a mole) are added to a liter of water, and
the sodium chloride is completely ionized, the boiling point will be elevated
1.04C. The mole of sodium will elevate it 0.52 and the mole of chlorine
will elevate it 0.52. Sometimes a substance that ionizes in solution is not
completely ionized. When this happens, the boiling point is elevated accord-
ing to the degree of ionization.
At high altitudes it is possible to cook foods more rapidly by adding salt
to the cooking water. To be very effective this requires such a large quan-
tity of salt that the food becomes too salty. It may be used for potatoes
that are not peeled.
Sugar solutions behave abnormally in regard to the boiling point. In
Experiment 4 it is found that the sugar solutions do not behave like the
salt solution. They do not reach a constant boiling point. A mole of sucrose
(342 grams) measures about 1^4 cups. It can be readily seen by consulting
the solubility table of sucrose that its solubility will account for only a
partial elevation of the boiling point. The boiling point of the sugar solu-
tion increases with its concentration until the melting point of the sugar
is reached. Occasionally, in cooking a sucrose solution (Experiment 4A),
some of the sucrose crystallizes on the edge of the pan, thermometer, and
top of the sirup, similar to the salt solution, but this is not the usual result.
CRYSTALLIZATION
49
When the melting point of the sucrose is reached these crystals melt.
Temperatures far above the melting point of the sugars can be obtained.
However, with the very high temperatures, caramelization or decomposi-
tion of the sucrose occurs quite rapidly.
There is no very satisfactory explanation for the abnormal behavior of
the sugars. Chemists tell us that one explanation may be that the sugar
and water combine chemically giving a new compound with a new boiling
point, or the combination of the sugar with the water may give a very
concentrated solution, thus elevating the boiling point.
Boiling point of sucrose solutions. Browne in his "Handbook on
Sugar Analysis" lists the boiling point of sucrose solutions as follows.
TABLE 10
BOILING POINT OF SUCROSE SOLUTIONS (Browne}
Per cent sucrose
10
20
30
40
50
60
70
80
90.8
Boiling point
100.4
100.6
101.0
101.5
102.0
103.0
106.5
112.0
1.SOO
A 10 per cent solution of sugar is one that contains 10 grams of sugar
and 90 grams of water or one having these proportions.
Heat of solution. Some substances that are soluble may liberate heat
when they go into solution. The example of mixing water and sulfuric
acid (H 2 SO 4 ) is a well-known one. Other substances, instead of giving
off heat, cause the temperature to drop when they go into solution. They
are said to have a negative heat of solution, and heat is absorbed.
If sugar and water of the same temperature are mixed, the temperature
of the solution drops as the sugar is dissolving. Salt and many other sub-
stances also absorb heat as they go into solution. When the substances that
absorb heat as they go into solution are crystallized from solution, heat
is liberated and the temperature is elevated slightly. This is often notice-
able in making fondant or fudge. Frequently the sirup softens so that it
is not so viscous and is easier to stir when crystallization starts. As the
first crystals formed are not visible, one may think that the sirup is not
going to crystallize because of this softening. It is more noticeable with
larger amounts of fondant and fudge than with very small ones.
Crystallization
In making icings, frostings, or candy like fondant and fudge, it is neces-
sary to crystallize the sugar solution. For crystallization to occur, nuclei
must form in the solution. To these nuclei the material of the solution is
added to form crystals. Both the rate of formation of nuclei and the rate
of crystallization are affected by the nature of the crystallizing substance,
50 SUGAR COOKERY
the concentration, the temperature, agitation, and the impurities present in
the solution.
Nature of the crystallizing substance. Some substances like salt
crystallize readily from water solution. It requires only a very slight super-
saturation to start nuclear formation, and all excess salt in the solution
beyond the saturation point is precipitated as crystals. Some substances do
not form nuclei or crystallize so readily as salt. With sucrose it is often
necessary to have a considerable degree of supersaturation before crystal-
lization commences. Sucrose crystallizes more readily than levulose.
Formation of nuclei. Nuclei cannot form and crystallization cannot
occur except from a supersaturated solution. The formation of nuclei, that
is the uniting of atoms to form nuclei, is influenced by several factors. If a
solution is left to stand, a few nuclei may form spontaneously in various
places, and from these nuclei crystallization proceeds. When only a few
nuclei develop spontaneously in the solution, the crystals grow to large
size. Usually nuclei formation and crystallization do not begin immedi-
ately after supersaturation occurs. The rate of nuclear formation may be
favored by specks of dust in the solution. Agitation or stirring of a solution
increases the rate of nuclear formation. A drop in temperature at first
favors, and then retards, the formation of nuclei. Instead of spontaneous
formation of nuclei, seeding a solution may be used to start crystallization.
Seeding. When crystals of the same material are added to start crystal-
lization the process is called seeding. These crystals serve as nuclei for
crystal growth. If the quantity of crystals added is large and the size
of the crystals small, it serves as many nuclei in the solution, and the
resulting crystals are small. If the quantity of material added is very
small, the nuclei formed are few in number and the crystals formed are
large. One may think of all crystals as being large enough to be visible,
whereas many of them may be very small, so small in fact that they may
float in the air. Tutton tells of crystals difficult to obtain, but after being
obtained several times in the laboratory they were then easily obtained.
If crystals are floating in the air there is the possibility that they may
serve to seed solutions, and thus start crystallization.
Rate of crystallization. To the nuclei formed in the solution new
molecules from the solution are deposited, in a regular order or manner,
so that each crystal has a typical shape. One side or face of a crystal may
grow more rapidly than another. The rate at which the nuclei grow to
larger size is called the rate of crystallization. This rate may be favored
by the concentration of the solution and its temperature; it may be hin-
dered by foreign substances.
Concentration of the solution. A more concentrated solution favors
the formation of nuclei. A fondant sirup cooked to 114C. contains less
water and is more concentrated than one cooked to 111C. Thus nuclei
form more readily in the one cooked to 114C. Large, well-shaped crystals
form more readily if the degree of supersaturation is not too great. The
ADSORPTION AND IMPURITIES IN THE SOLUTION 51
most favorable supersaturation for crystal growth, of a sucrose solution
boiled to 112C, is that between 70 and 90C. Although crystallization
occurs in a very short time when the sirup is stirred at these temperatures,
the crystals formed are larger than when the sirup is cooled to a lower
temperature. See Figs. 1 and 3. Supersaturation and a low temperature
are desirable for the development of small crystals. The viscosity of a very
supersaturated sirup delays crystal growth.
Temperature at which crystallization occurs. It is a well-known
fact that, in general, chemical precipitates come down more coarsely
crystalline if crystallized at high temperatures. Barium sulfate is a good
example of a substance that crystallizes in large crystals at high tempera-
tures. The sugars follow this general rule. Other things being equal, i.e.,
concentration, etc., the higher the temperature at which crystal formation
occurs, the coarser the crystals formed.
A drop in temperature at first favors the formation of nuclei, and then
hinders it. Crystallization is favored in sugar sirups by cooling to a certain
temperature, but is hindered when cooled to a lower temperature. Since
the viscosity of a saturated sugar solution becomes increasingly greater as
the temperature falls below 70C., crystal formation is also slower as the
temperature falls.
Agitation. Stirring a solution favors the formation of nuclei and
hinders the depositing of the material of the solution on the nuclei already
formed. Hence, crystals in solutions that are stirred do not develop to
the size that they do in spontaneous crystallization. Bancroft states that
"The mean size of crystals is determined by the total amount of the
material crystallizing and number of crystals. The really important thing
therefore is the number of nuclei which are formed under any given
conditions." If small crystals are desired, then the conditions should be such
that many nuclei are formed. Small crystals are obtained in sirups of
definite concentration and temperature, if the sirup is stirred until the
mass is kneadable. However, if the sirup is stirred for only a short time,
some nuclei are formed, but after agitation is stopped, the formation oj
new nuclei is not favored and crystal growth is favored. Fig. 2 shows
crystals from fondant stirred for only a few seconds. The crystals are
much larger than those in Fig. 1, which shows crystals from fondant that
was stirred until the mass could be kneaded. The same thing is illustrated
in Fig. 10, which shows crystals from divinity that would not quite hold
its shape but spread when dropped on oil paper. The crystals from the same
divinity (Fig. 9) which was stirred until it would hold its shape, but was
glossy and not dry in appearance when dropped on oil paper, are small.
Divinity with the small crystals is very smooth and velvety on the palate.
This emphasizes the importance of stirring candy and icing sirups until
practically all the material is crystallized, if small crystals are desired.
Adsorption and impurities in the solution. Freundlich states that
"in the vast majority of cases the foreign substance lowers the rate of
52 SUGAR COOKERY
crystallization." The rate of crystal growth is retarded because of adsorp-
tion of the foreign substance by the crystals. If the substance is strongly
adsorbed, crystallization may be retarded to such a rate that it is practically
abolished, even though the solution is very supersaturated with the crystal-
lizing substance. Since the adsorption prevents crystal growth, if a pre-
cipitate is formed in the presence of a substance strongly adsorbed by the
precipitate, it will crystallize in a much finer state of subdivision. Some-
times the substance is more strongly adsorbed at one face than at another,
so that this face grows more slowly than is customary and thus becomes
comparatively larger in relation to other faces. This explains why crystals
from pure solutions may have different shapes from those obtained from
impure solutions. Speaking of sugar manufacture and crystallization of
sucrose, Zitkowski says, "If the content of non-sugars in the solution is
high enough crystallization may be prevented even though evaporation is
carried to the point of dryness." The addition of other carbohydrates, such
as dextrose, levulose, and starch, to sucrose solutions retards the crystal-
lization of the sucrose. The extent to which they delay crystallization
depends upon how strongly they are adsorbed and the proportion added.
Other substances strongly adsorbed by sucrose crystals are fat and
proteins. Hence, the use of butter, milk, and egg white all retard crystal
growth.
Crystallization of sucrose in sugar manufacture. In sugar manu-
facture, when it is time to start crystallization in the mass of boiling sirup,
the sugar boiler may lower the pressure, w r hich causes violent boiling or
agitation, or he may add a sirup or water to change the concentration or
temperature. He may also seed the sirup by adding a sufficient amount of
small sugar crystals. The crystals when first formed are too small to be
visible in the sirup but grow to visible size. This may be in a few moments.
The sugar boiler controls the temperature, pressure, and density to bring
the crystals to the desired size. If they are too small when finished, too
much sugar is lost in washing the liquid from the crystals. If they are too
large, the public does not care for them.
Grades of sugar. Rice states that there is a surprising lack of informa-
tion about the various grades of sucrose sugar produced and their specific
uses, probably because the information has not been given general circula-
tion. He lists 36 grades of sucrose, to which may be added many more
grades made for a specific use with a particular equipment. The following
classifications are those given by Rice.
The refined sugar distributed for household use is somewhat smaller
in grain size than that found some years ago, because the general demand
has been for a more rapidly dissolving sugar. As the finer grain gives a
whiter appearance, the tendency has been to produce a finer sugar. Fine
Granulated is produced in the largest quantity of any grade. In the same
class, each with increasingly finer grain or crystal size, are Extra-fine
Granulated, Berry or Fruit or Fruit Powdered (it is designated by all
GRADES OF SUGAR 53
these names), and Coating. Rice states the name Fruit Powdered has
nothing to do with fruit nor is the sugar powdered. The "Coating" is used
where unusually fine crystals are desired.
Four sugars, produced especially for use when high-temperature cooking
is necessary in making clear hard candies and very white fondants or pan-
coated goods, or when an extremely hard grain must be used, are Coarse,
Standard, Medium, and Manufacturers' Grade. Manufacturers are tend-
ing to use Manufacturers' Granulated, which varies from the others only
in that it is the finest of the four and will dissolve much faster. In this
same class are the Sanding sugars. Sanding sugars are used to sprinkle
upon the surfaces of many soft candies and fruit products to prevent their
sticking together. They are also used to sand gum drops and fruits which
are to have further quantities of sugar crystallized upon their surfaces. The
crystals of Sanding sugar are generally nearly perfect and exact in size.
There are generally produced three grades of machine powdered sugar
differing only in the degree of fineness: Coarse Powdered, having about
the fineness of Coating sugar; Standard Powdered, being somewhat finer;
and XXXX, commonly known as Confectioners', being as fine as practical
to produce with the ordinary type of sugar mill. A still finer powdered
sugar, made with an improved powdering mill, is sometimes designated as
6X or Special XXXX. This last sugar is particularly valuable in prepar-
ing cold icings, because they remain softer longer than when prepared
with coarser powdered sugars. The smaller the particle size the greater
the amount of moisture held, because of the proportionally greater surface
area. Rice states the number of X's applied to different sugars means
nothing in actual fineness. Powdered sugars may be treated to prevent
caking. Usually 3 per cent of cornstarch is added. A tri-calcium phosphate
has been introduced for this purpose and 1 per cent of it is more effective
than 3 per cent of cornstarch. Its use is not as yet permitted in some states.
Rice describes a new and different sugar called transformed sugar. It is
produced in the same way as refined sugar up to the point of crystallization.
It is then treated to give a very small grain with exceedingly irregular
surface, the surface being penetrated by cracks or recesses which cause the
grain to crumble easily, and, because of the relatively large surface, to
dissolve almost instantly when dropped into water. The particles may be
crushed easily and are used in chocolate coatings. "The crevices in these
grains are very small and naturally are full of air. When this sugar is used
for creaming with shortening in the production of cake or in very dry
dough for biscuits, this finely divided air cannot collect and escape in large
bubbles but acts as a leavening agent and reduces the necessity for most, if
not all, other leavening agents." Because of its fine and fluffy condition it
can replace powdered sugars in various prepared drinks and food mixtures.
At present there are seven grades of transformed sugar, varying in fluffiness
and color.
Soft brown sugars are graded according to color and range from a nearly
54 SUGAR COOKERY
white No. 1 to No. 15, which is as dark as roasted coffee. The grain of
these sugars is softer than that of refined sugar and the percentage of invert
sugar increases with increasing darkness in color.
Amorphous sugar. When sucrose is melted, or when solutions of
sucrose are heated to high temperatures and then allowed to cool, crystal-
lization does not occur immediately. A very brittle, very hard, solid,
transparent mass is formed. This form of sucrose is known as amorphous
sugar. It crystallizes very slowly, sometimes taking several months or
years to crystallize. Candies of this type are extremely hard. Some candies
are cooked to stages between those of the soft crystalline ones and the
hard amorphous forms. Caramels are examples of this type of candy
they are fairly soft, yet are not crystallized.
Crystallization in candy making. Large crystals are the result of
growth, for which several days or weeks may be required. The growth
of the crystals is favored if the solution is not stirred, if the supersatura-
tion is not great, and if no crystals are added to the solution. Since small
crystals are desired in candy making, the procedure followed is the op-
posite of that for obtaining large crystals. The period of crystallization
is short, usually not over 30 minutes is required, the supersaturation is
great, and the solution is stirred after supersaturation is attained.
Stages of Cookery of Sucrose Solutions in Candy Making
The "cold-water" test. In the "cold-water" test, one can tell, from
the firmness or hardness of a portion of the sirup which has been dropped
into cold water, whether the sirup has reached a concentration required
for the type of candy desired. The degree of firmness in the cold-water
test is designated by different descriptive terms, such as soft ball, medium
ball, hard ball, and brittle. It should be remembered that there is no
definite stage between a soft ball and a medium one, but as the concen-
tration of the solution gradually increases, the firmness of the sirup tested
in cold water increases. One factor that causes variations in this test is the
fact that the colder the water in which the sirup is tested the firmer the
tested portion. Another cause for variation is that the portion being tested
is not always left long enough to become cooled.
Yet with long practise the cold-water test can be used with great preci-
sion to denote the stage of cookery of a sirup. It is the different interpreta-
tions of what constitutes a soft or medium ball that makes this test a more
difficult one to use. The number of terms used by different persons to sug-
gest the same stage of cookery is illustrated by the following. In looking
over a large number of recipes for a candy contest, it was interesting to
find that of 600 recipes nearly 200 had exactly the same proportion of
sugar, corn sirup, water, and egg white. But the directions for making the
cold-water test in these 200 recipes varied. Here are some of the terms used
to describe the portion of sirup tested in the cold water : Soft ball, medium
ADDITION OF CORN SIRUP AND OTHER SUGARS 55
soft ball, medium firm ball, firm ball, hard ball, solid ball, real hard, very
hard, hardens, threads, soft crack, cracks, crackles, cracks and hops, hairs,
spins hairs, strings, snaps, breaks, and brittle.
Stages of cookery. In part the descriptions of stages of cookery of
sugar sirups are from "Terminology Used in Food Preparation." A sucrose
solution that has reached a concentration indicated by a temperature of
110 to 112C. does not form a ball when a portion of the sirup is tested
in ice water, but spins a two-inch thread when dropped from a fork or
spoon.
At a temperature of 113 to 115C. a soft ball is formed when a
portion of the sirup is tested in ice water. This ball is easily molded in the
water, but does not retain its shape at room temperature. Sirup cooked to
this stage is used for fondant, fudge, and penuchi.
At a temperature of 118C. a firmer ball is obtained. At 122C. the
ball is still harder and less readily molded in the water. At 122C. the
ball retains its shape at room temperature. Sirups for caramels are cooked
to 118 to 122C. Temperatures of 118 to 123C. are used for sucrose
sirups that are to be poured over beaten egg white.
The sirup at temperatures of 121 to 130C. forms an increasingly
harder ball, which holds its shape, yet is plastic, when a portion is dropped
into ice water; it is used for popcorn balls, nougat, divinity, and some
taffies. The sirup at temperatures of 132 to 143, called the soft-crack
stage, separates into threads which are hard but not brittle when dropped
into ice water. It is used for butterscotch and taffies. Sirups cooked to 149
to 154C., the hard-crack stage, separate into separate threads which are
hard and brittle when dropped into cold water ; used for brittles and glaces.
The length of the thread or hair that forms when a fork or spoon
containing some of the sirup is lifted into the air may also be used to
indicate the stage of cookery.
Effect upon stage of cookery of addition of corn sirup and
other sugars to sucrose solutions. The addition of corn sirups and
other sugars to sucrose solutions modifies the firmness of the portion tested
at a definite temperature in cold water.
Commercial corn sirup is composed of dextrin, dextrose, maltose, water,
and a small amount of ash. Frandsen, Rovner, and Luithly state that its
composition is as follows :
PER CENT
Dextrin 29 . 8 to 45 . 3
Maltose 4.6 to 19.3
Dextrose 34 . 3 to 36 . 5
Ash 0.32 to 0.52
Water .- 14.2 to 17.2
Since the composition of corn sirups may vary slightly, this may result
in different degrees of firmness when different corn sirups are used with
56
SUGAR COOKERY
sucrose solutions. The use of corn sirup with sucrose in taffy, brittles, or
caramels, candies that do not require crystallization, produces a definite
stage of hardness when determined by the cold-water test at a lower
temperature than when sucrose is used alone. Dextrin is the ingredient of
the corn sirup that brings about this result, for if dextrin is used alone with
sucrose the temperature for a definite degree of hardness is still lower than
when corn sirup is used. In some of the early references on sugar cookery
the term glucose is used for corn sirup.
Table 1 1 shows the effect of different proportions of sugar upon the
stage of hardness in sugar cookery. Miss Daniels has reported similar
results in part.
TABLE 11
Amt. of
Amt. of
Amt. of
Amt. of
Soft
Medium
Hard
Cara-
dextrin
corn
sucrose
dextrose
ball
ball
ball
Crack
melized
sirup
Temp.
Temp.
Temp.
Temp.
Temp.
1 cup
1 cup
107
109
114-118
2 cups
109
111
114
120
135
1 cup
1 cup
110-111
113
115-116
120-122
140
1 cup
2 cups
112
114-115
118-120
126-128
145-150
2 cups
113-115
118
122
132
155-170
1 cup
1 cup
118
122
132
140-145
2 cups
125-128
132
140
It can be seen from this table that the greater the proportion of corn
sirup used the lower the temperature to which the sirup needs to be
cooked for a definite stage of hardness.
Fondant
Fondant is made when sucrose is cooked with water to a definite
temperature, the sirup is cooled and beaten, and the mass crystallizes.
According to accepted standards for good fondant, it should be snowy
white. The crystals should be so small that they are imperceptible and
not gritty on the palate. The fondant should be soft enough to be plastic
and velvety but not dry and crumbly.
Cooking of fondant. Enough water should be added to dissolve all
the sugar during the cooking period. With rapid boiling a larger proportion
of water can be used. With a slow fire and slow boiling, it is preferable to
use less water, or a long time is required for the cooking process. With
larger quantities of sugar the proportion of water is reduced because
CONCENTRATION AND TEMPERATURE 57
evaporation is relatively more rapid from the small quantity of sirup.
Covering the pan during the first part of the cooking period allows the
steam to dissolve and wash down crystals from the sides of the pan.
Some directions state not to stir the sirup while it is boiling. It is well
to stir it to be sure all the sugar is dissolved, so that there are no crystals
in the sirup to start crystallization while it is cooling. The danger in
stirring candy while it is boiling comes from splashing the sirup on the
sides of the pan. These drops of sirup on the side of the pan become dry
and nuclei form which serve as a basis for crystallization while the sirup
is cooling. A damp cloth is often used to swab the sides of the pan to
prevent nuclei and crystals forming there during the cooking of the sirup.
Since boiling solutions of sugars are not saturated solutions, any candy
can be stirred as much as desired while it is boiling without causing
crystallization, provided the sirup is not splashed on the sides of the pan.
But after the sirup stops boiling it cools quickly and soon reaches the super-
saturation point. If the sirup is poured for cooling from the pan in which
it is cooked, it should be done quickly. Directions often state not to scrape
the portion clinging to the pan with the spoon. Of course this is because
the small amount of sirup left on the sides of the pan soon cools to the
supersaturation point, and if it is stirred, as it must be in scraping it
from the sides of the pan, crystals may form that will seed the entire
mass. The thermometer should not be allowed to roll around in the sirup
while the sirup is cooling for this agitates the sirup. The pan should be
set level so that all parts of the sirup cool equally. The container in which
the fondant is poured to cool should have a smooth surface, as rough
surfaces may induce crystallization.
In the preceding pages the factors determining the size of crystals in
sugar crystallization are discussed. These factors are applicable in making
fondant and fudge.
Concentration and temperature for cooking the sirup. A sucrose
solution containing 80 per cent of sucrose, i.e., 80 grams of sucrose and
20 grams of water, boils at 112C., is saturated at 90C. and super-
saturated below 90C. Therefore, no crystals are formed in a sucrose
solution cooked to 112C. until the temperature drops below 90C.
Woodruff and van Gilder found that fondant cooked to 115C. has an
average water content of about 13 per cent. The higher the temperature
to which the sirup is cooked, the less the percentage of water in the fondant.
If fondant contains too small a proportion of water, it is dry and crumbly ;
if too much, it is sirupy and runny. When the sirup is cooked to 109 to
111C. (Experiment 7B), the fondant contains a high percentage of
moisture. Sirups cooked to this temperature give a fondant too fluid to
knead or mold, unless it is beaten when hot. Fondant sirup for ordinary
home use may be cooked from 113 to 115C. The lower temperature
gives a softer fondant for remelting and making candy like peppermints;
the higher temperature gives a drier fondant for molding. It should be
58
SUGAR COOKERY
FIG. 1. Crystals from fondant. The sirup was cooked to 113C. then beaten
immediately until the mass was stiff enough to knead. Magnification approxi-
mately x 200.
FIG. 2. Crystals from fondant. A portion of the same sirup as that in Fig. 1.
It was beaten slightly while hot to start crystallization; then left to stand several
hours until the whole mass was crystallized. Magnification approximately x 200.
(Photomicrographs of sugar crystals by courtesy of EtJiel L. Sivanson.)
SUGAR COOKERY
FIG. 3. Crystals from fondant. A portion of the same sirup as that shown in
Fig. 1. Cooled to 40C. Then beaten until the mass was stiff and kneadable.
Magnification approximately x 200.
--T;^'
FIG. 4. Crystals from fondant. A portion of the fondant shown in Fig. 3,
immediately after adding 6 per cent of beaten egg white. Magnification approxi-
mately x 200.
60
SUGAR COOKERY
FIG. 5. Crystals from fondant. A portion of the same fondant shown in Fig. 3
after 20 days' storage. Note aggregation of the crystals. Magnification approxi-
mately x 200.
.
< } A \
FIG. 6. 'Crystals from fondant to which 6 per cent egg white v as added after
20 days' storage. Compare with Fig. 4. Magnification approximately x 200.
SUGAR COOKERY
61
FIG. 7. Crystals from fondant. A portion of the same fondant shown in Fig. 3
after storage for 40 days. Note the growth of crystals. Magnification approxi-
mately x 200.
FIG. 8. Crystals from fondant, with 6 per cent of added egg white after 40
days' storage. A comparison with crystals in Fig. 4 and Fig. 7 shows that egg
white tends to retard crystal growth during storage. Magnification approxi-
mately x 200.
62
SUGAR COOKERY
IP
tfl
FIG. 9. Crystals from divinity which was beaten until a piece dropped from
a spoon would hold its shape, yet still appear glossy. Magnification approxi-
mately x 200.
T
Y-* r
r
FIG. 10. Crystals from divinity. Some of the same divinity as that shown in
Fig. 9. But these pieces were not beaten as long as those in Fig. 9. They flattened
out when dropped from a spoon. These crystals and those shown in Fig. 2
emphasize the importance of beating candy sufficiently. Magnification approxi-
mately x 200.
SUGAR COOKERY
63
e-<^ i>S/r .,; -^
PJ^^^f
%Sv* ',JX
FIG. 11. Crystals from divinity. Same as those shown in Fig. 9, but after
40 days' storage. Compare with crystals in Fig. 7 and Fig. 8. Magnification approxi-
mately x 200.
FIG. 12. Corn sirup, sucrose and water cooked to 119C. and beaten while
hot until the mass was stiff. Corn sirup retards crystal growth, see Fig. 1, but
not to the same extent that both corn sirup and egg white do. See Fig. 9. Magnifica-
tion approximately x 200.
64 SUGAR COOKERY
remembered that evaporation is greater from a small quantity of fondant,
while it is being stirred, than from a large quantity. On rainy or damp
days, when the humidity is high, moisture may be absorbed from the air
by the sirup, so that it is preferable to cook the sirup to the higher tem-
perature. Cooking the sirup to a temperature above 116C. gives a fondant
that is too dry and crumbly. Jordan states that commercially the amount
of moisture in fondant is controlled carefully and according to the use for
which it is intended, as a difference of 1 per cent of moisture results in a
fondant too soft to handle or too dry to knead.
The growth of crystals in fondant. Freundlich states that "surface
tension is also the cause of recrystallization, in which small crystals unite
to larger ones. Probably this phenomenon is similar to the union of minute
droplets to larger ones, when in direct contact, for it is unlikely that the
formation of larger crystals could be due to the increased vapor pressure
of the smaller ones bringing about a distillation ; the process takes place far
too rapidly to allow of the latter explanation." Water in fondant is a
saturated sucrose solution. The crystals are in contact with this saturated
solution. Owing to the higher surface energy of small crystals, as dis-
cussed in Chapter I, the smaller crystals dissolve, and the larger crystals
increase in size.
Crystals in fondant may grow in size during storage. Halliday and
Noble have reported the growth of crystals in fondant stored for 17 days.
Figs. 3 to 8 show crystals from fondant. Fig. 7 shows the growth of
crystals in fondant after 40 days' storage. Compare these crystals with
those shown in Fig. 3.
The addition of egg white to fondant. Egg white may be added
to fondant. Paine states that the clumping together of air particles into
larger particles lessens the intensity of the white and that the addition
of a small quantity of egg white to fondant prevents the aggregation of
the air particles, thus aiding in keeping the fondant white. The beaten egg
also incorporates additional air.
The addition of beaten egg white to fondant also retards the rate of
crystal growth during storage. Figs. 4, 6, and 8 show crystals from
fondant to which egg white has been added. Since the egg white is ad-
sorbed by the crystals, the effectiveness of the egg white in preventing
crystal growth may partially depend upon how the egg white is distributed
throughout the fondant. Swanson found that not much more than 6 per
cent of beaten egg white could be added to the fondant, without the
fondant becoming too fluid. She found 3 per cent of added egg white to
be as effective as 6 in preventing growth of crystals during storage.
The addition of dextrose, levulose, or invert sugar to fondant.
Dextrose, levulose, or invert sirup may be added directly to sucrose solu-
tions to aid in regulating the size of the crystals. Or, invert sugar may be
formed during cooking of the sucrose sirup by adding citric, tartaric, or
acetic acids. Often cream of tartar is used for inverting sucrose in fondant.
COLOR OF FONDANT 65
It is difficult to regulate conditions, such as the time of cooking, to obtain
a definite percentage of invert sugar for sucrose is inverted more rapidly
with higher temperatures and greater acidity. Hence, it is sometimes pref-
erable to add a definite quantity of dextrose, levulose, or invert sugar.
Woodruff and van Gilder found that cream of tartar inverted the sucrose
more slowly than citric, tartaric, or hydrochloric acids at the same pYL.
Cream of tartar can be added in sufficient quantity to produce enough
invert sugar to give small crystals and to add to the smoothness of the
fondant. If added in too large a quantity, too much invert sugar is formed,
so that the fondant is too fluid. The flavor of the fondant is quite acid
when a large proportion of cream of tartar is used.
The larger the quantity of dextrose or levulose added in making
fondant the longer the time required to beat the sirup to bring about
crystallization. With too large a proportion of these sugars the fondant
is soft. When fluid centers of confections are desired, it is necessary to add
substances that bring about inversion of the sucrose after the fondant is
dipped in chocolate or treated in some way to give a firm outer coating.
Woodruff and van Gilder state that sirups with concentrations of 43 per
cent or more invert sugar would not crystallize; those containing 16 to 23
per cent formed a semi-fluid mass of crystals; and those containing 6 to 15
per cent gave a plastic, moldable product. With 11.1 per cent or more of
invert sugar the crystals of maximum size measured 10 to 13.2 microns
and the grain was exceedingly fine to tongue and roof of the mouth.
Fondants containing 7 per cent reducing sugars of either kind (glucose or
levulose) were of agreeably fine texture, with their largest crystals measur-
ing 15 to 19 microns. Crystals in candies of observed coarse texture meas-
ured 45 or more microns. Differences in crystal size of 6 to 10 microns,
which was the difference of crystal measurements of fondants rated very
fine and slightly coarse, could be detected by the tactile sense.
Halliday and Noble have reported that the addition of corn sirup,
which contains dextrose and dextrin, tends to prevent the growth of
crystals during storage of fondant. They also found that fondant made
with cream of tartar retarded crystal growth during storage.
Color of fondant. Fondant crystallizing without stirring is not snowy
white but more transparent. The snow-white appearance of the stirred
fondant is due to the small air particles. When the water contains alkaline
salts the fondant without cream of tartar added has a yellow or gray
tinge ; that with cream of tartar or acids is white.
Fondant made with hard water, pH 7.2 to 7.8, has a creamy tint. This
may be caused by slight traces of flavones in the sugar, but it is probable
that it is due to caramelization or some other cause. If, to some of the same
sugar and water, a little cream of tartar is added, a snowy white fondant
is always obtained. If, however, corn sirup is added to the sugar to make
fondant with the above water a gray color develops. The color is so pro-
66 SUGAR COOKERY
nounced that the fondant is not attractive looking. If distilled water is
used with the corn sirup and sucrose, the gray color does not develop.
Ripening. When fondant stands 12 to 24 hours it seems more moist
and is more plastic and kneads more easily than when it was first made.
In the candy trade this is known as ''ripening." Fondants that contain
substances that cause slow hydrolysis of the sucrose become softer on
account of the formation of invert sugar, but "ripening" is an additional
process and occurs in fondant containing only sucrose. Carrick suggests
that the reason for this "ripening" is that the small crystals in the mass
are dissolved, thus letting the large crystals move more easily, and they are
thus more plastic.
Honey fondant. Candies made from pure honey, on account of their
high levulose content and the moisture-absorbing property of honey, usually
become very sticky in a few hours after they are made. Phillips reports the
combination of honey, whole milk, and lactose sugar to make fondant.
Stratton combined honey and lactose in fondant. Fondant usually contains
some crystals of each of the sugars that enters into its composition, but in
Stratton's combination the crystal phase was entirely lactose, the crystals
being particularly minute. But the lactose crystals have a tendency to grow
so that fondants smooth at first became somewhat grainy. It was found
that the honey fondant would absorb a relatively high percentage of whole
milk by mechanical mixing, and that this milk tended to prevent the growth
of the lactose crystals. It was also found that the honey has an unusual
preservative action, for the milk in the mixture remained sweet as long as
the candy was kept.
Fudge
The factors that control the size of the crystals in fondant making
also determine the size of the crystals formed in fudge. Fudge is often
made of brown sugar. Brown sugar contains a higher percentage of invert
sugar than granulated sugar. Thus it crystallizes less readily than granu-
lated sugar.
Fudge also ripens with storage and if placed in a container with a
tight-fitting lid becomes much softer and more velvety after 24 hours'
storage.
In substituting cocoa for the chocolate in fudge, Reese found that the
quantity of cocoa was a matter of individual preference, although 3 to 3^
tablespoons to each cup of sugar was preferred by the majority of judges.
But, if other conditions were standardized, the final temperature to which
the sirup was cooked depended upon the proportion of cocoa used. Cocoa
contains considerable dextrin. It is probably the presence of this ingredient
that affects the consistency of the sirup so that with increasing amounts of
cocoa the temperature to which the sirup is cooked should be lower. For
a sirup cooled to 40C. and requiring about 12 to 15 minutes to beat to
THE AMOUNT OF MILK IN CARAMELS 67
bring about crystallization, the fudge containing 1 tablespoon of cocoa is
cooked to 112.5 or 113C. For each additional tablespoon of cocoa the
temperature to which the sirup is cooked can be lowered one-half degree.
These conditions hold for the recipe given in the laboratory outline. With
larger proportions of butter, the temperature to which the sirup is cooked
should be elevated.
Caramels
Caramels, taffy, and brittles are types of candy that are firm but not
crystallized. To prevent crystallization larger quantities of dextrose, levu-
lose, corn sirup, or other substances are added than when making fondant
or fudge. If these substances are not added directly, then larger quantities
of substances that produce inversion of sucrose are used, thus giving a
higher percentage of invert sugar.
Corn sirup and molasses are the materials most commonly used in
caramels to prevent crystallization. The temperature to which caramels are
cooked depends upon the ingredients used to prevent crystallization and
their proportion. With increasing amounts of corn sirup, because of its
dextrin content, the temperature to which the caramels are cooked is
lowered. But with molasses or honey the temperature to which the caramels
are cooked is much higher than when corn sirup is used. In the recipe given
in the experimental outline with 1 cup of corn sirup to 2 cups of sucrose,
a temperature of 119 to 120C. produces the degree of firmness liked by
most people. If the corn sirup is increased to 2 cups and the sucrose re-
duced to 1 cup the same firmness is produced by cooking to a lower tem-
perature or 116 to 117C. If dextrose, honey, or molasses is substituted
for the corn sirup, the temperature to which the sirup must be cooked to
give the same firmness is above 120, sometimes as much as 126C. or
higher, the temperature depending on the type of molasses or the pro-
portion used.
Sugar reactions with proteins. Ramsay, Tracy, and Ruehe found
that when milk, albumin, or casein is heated with lactose or dextrose a
brown discoloration occurs. As the temperature is raised dextrose and casein
become so firmly attached to each other in a protein-sugar complex that no
amount of washing will remove the sugar.
The amount of milk in caramels. A large quantity of milk in cara-
mels develops a flavor that can be obtained in no other way. Slow cooking
develops more of the brown color and flavor than rapid cooking. The
color comes from lactose-protein and dextrose-protein compounds and the
caramelization of the lactose with high temperatures and long cooking.
If all the milk is added when cooking is first started the milk may curdle.
If most of the milk is added slowly after the sirup is thick it very seldom
curdles. In using large quantities of milk in caramels the protein of the milk
will tend to prevent crystallization.
68 SUGAR COOKERY
Large quantities of fat increase the richness of caramels.
Caramels are stirred or handled as little as possible after the sirup
stops boiling until they are cool. After the boiling is stopped they soon
reach the saturation point, which for caramels is above 100C., and
stirring the sirup or scraping the pan tends to produce crystals.
Taffy
Taffies or pulled candies have vinegar, lemon juice, or cream of tartar
added during cooking. These substances cause inversion of the sucrose,
which prevents crystallization. Dextrose, corn sirup, or molasses may be
added to the sucrose to prevent crystallization. Pulled taffies become white,
or if made with molasses become much lighter in color, on account of the
air bubbles incorporated during pulling.
The cooking temperatures of pulled candies vary according to the
ingredients and their proportion used, but follow the same general rules
as for caramels. Those containing large quantities of corn sirup are cooked
to lower temperatures. Taffies are firmer than caramels and are there-
fore cooked to higher temperatures.
Brittles
Brittles are much harder than caramels or taffies and are cooked to
high temperatures. At the temperatures to which they are cooked carameli-
zation of the sugar may take place, and this as well as added substances
tends to prevent crystallization. If caramelization is very extensive, a
number of decomposition products of sugar may develop, among which
are some acid substances. The greater the amount of caramelization the
stronger the flavor developed. Soda is often added to brittles. It not only
neutralizes the acidity developed and lessens the bitter flavor but owing to
gas formed gives a porous texture to the brittle.
LITERATURE CITED AND REFERENCES
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Ice Cream Mix. Ice Cream Trade J. 14: No. 4, 29 (1918).
Bancroft, W. D. Supersaturation and Crystal Size. J. Physical Chem. 24: 100
1920).
Biester, A., Wood, W. W., and Wahlin, C. S. Carbohydrate Studies. I. The
Relative Sweetness of Pure Sugars. Am. J. Physiology 73: 387 (1925).
Bingham, E. C. Fluidity and Plasticity. McGraw-Hill Co. (1922).
Browne, C. A. A Handbook of Sugar Analysis. J. Wiley & Sons (1912).
Browne, C. A. Moisture Absorbing Power of Different Sugars and Carbohydrates
under Varying Conditions of Atmospheric Humidity. Ind. Eng. Chem. 14: 712
(1922).
Bryant, A. P. Factory Control in the Manufacture of Cornstarch and Corn Sirup.
Ind. Eng. Chem. 8: 930 (1916).
REFERENCES 69
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Daniels, A. L., and Cook, D. Factors Influencing the Amount of Invert Sugar
in Fondant. J. Home Econ. 11: 65 (1919).
Daniels, A. L., and Troxell, M. The Influence of Glucose on the Cooking Tem-
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Daniels, A. L. The Influence of Glucose on the Cooking Temperatures of Candy
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Duryea, C. B. Industrial Maltose. Ind. Eng. Chem. 6: 419 (1914).
Frandsen, J. H., Rovner, J. W., and Luithly, J. Sugar Saving Substitutes in Ice
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(1921).
Gray, G., and McMullen, G. Temperatures for Candies and Frosting Sirups at
High Altitudes Above Sea Level. J. Home Econ. 15: 119 (1923).
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Gillis, J. Le Systeme: Maltose Eau. Recueil des travaux chimiques des Pays-Bas
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Halliday, E. G., and Noble, I. T. Hows and Whys of Cooking. University of
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Haworth, W. N. The Molecular Structure of Carbohydrates. Chem. and Ind.
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Hudson, C. S. Further Studies on the Forms of Milk Sugar. J. Am. Chemical
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Hudson, C. S. American Sources of Supply for the Various Sugars. Ind. Eng.
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Hunziker, O. F., and Nissen, B. H. Lactose Solubility and Lactose Crystal Forma-
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Jackson, R. F., Silsbee, C. G., and Proffitt, M. J. The Preparation of Levulose.
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70 SUGAR COOKERY
Phillips, E. F. Overcoming Difficulties in the Use of Honey. Food Ind. 7: 61
(1935).
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SUGAR COOKERY
Laboratory Outline
Keep a record of the experiments performed in a permanent note book.
The experiments should be written up under the following headings.
The object of the experiment, what happens, the results, and most impor-
tant, the conclusion drawn or the application of the results in preparation
of food. Suggestive headings for record of what happens are given under
most of the experiments,
Experiment 1.
To determine the relative solubility of the various sugars.
Measure 20 cc. of water for each sugar to be used. Place in a Pyrex cup or
a glass. Take the temperature of the water. Weigh the following amounts
of sugar.
LABORATORY OUTLINE
71
Sucrose 60 grams
Levulose 70 grams
Dextrose 20 grams
Maltose 20 grams
Lactose 5 grams
Add a small portion of the sucrose to one of the containers of water. Stir
until all is dissolved. Add another portion of sucrose and continue until you
have as much of the sucrose in solution as can be dissolved. Take the tem-
perature of the solution while the sugar is dissolving. The stirring should be
continued at intervals for 1 hour. Weigh the sucrose that is left and subtract
the amount from 60 grams to obtain the amount dissolved. Your results will
be only approximate for solubility should be determined in flasks to prevent
evaporation. However, the results that you obtain will show the compara-
tive solubility of the different sugars. If any undissolved sucrose remains
after stirring for some time, set the container in warm water and stir until
all the sucrose is dissolved. Put the container away in the laboratory and look
at it occasionally to watch the growth of crystals. Compare the crystals formed
with those of other sugars.
Repeat the above directions for each sugar. For the less soluble dextrose and
maltose add smaller portions when dissolving the sugars. Lactose has the least
solubility of the above sugars and should be added in very small portions.
Kind of sugar
Grams
dissolved
Temperature
of water
at first
Temperature
while sugar
is dissolving
Sucrose
Levulose
Experiment 2.
To determine the boiling point of water at the elevation above sea level at
which you live.
Place 1 pint of water in a sauce pan. Heat slowly. Notice the temperature
at which bubbles begin to form on the sides and bottom of the pan. Of what
are these bubbles formed? What becomes of them? At what temperature do the
vapor bubbles begin to form? Do the first ones reach the surface of the water?
At what temperature does the water boil? Are you at sea level or above it?
What is the boiling point of water at sea level? Observe the surface of the
liquid and the size of the bubbles. Heat the water so that the bubbles form
rapidly. Is the temperature the same as when the bubbles form slowly? How
do the surface of the water and the size of the bubbles compare with those
of the slow-bubbling liquid? Does the temperature rise? Explain.
Compare the temperatures registered by the thermometer when held in the
water so that the thermometer bulb does not touch the bottom of the pan and
when it touches it. Compare the temperatures registered when the bulb of
72
SUGAR COOKERY
the thermometer is only partially immersed and when it is immersed so that
there is y* to 1 inch of water above the bulb. How should you apply these
results to cooking sirups to a definite temperature in class results? Is the tem-
perature the same when the thermometer bulb touches the bottom at the
center and at the sides of the pan? (This may or may not vary according to
the type of gas burner or the electric unit used.)
Temperature
Temperature
Type of
bubble
Breaks
Slow-
bubbling
liquid
Rapid-
bubbling
liquid
When bulb of
thermometer
is partially
immersed
When bulb
touches the
bottom of pan
Results and conclusions.
Experiment 3.
To determine the effect on the boiling point of water when a soluble sub-
stance is added.
To 1 cup of water add a scant ]4 cup of salt. Heat to the boiling point.
Note the temperature. Continue boiling. Does the temperature change? Con-
tinue boiling until the temperature remains constant. What other change
occurs? What is the effect on the boiling point when salt is added to water?
Results and conclusions.
Experiment 4.
To determine the boiling temperature of sugar sirups corresponding to the
"cold-water tests" used in candy making.
A. Sucrose sirup.
Dissolve 1 cup of sucrose (granulated sugar) in ^ cup of water. (The
proportion of sugar and water used may need to be increased. The quantity
of sirup should be sufficient to cover the thermometer stem to a depth of j/2
inch above the bulb. The amount of sugar needed depends upon the size of the
pan and the length of the thermometer bulb.) Bring the solution to boiling.
Note rise in temperature with constant boiling. Explain. Why can a higher
temperature be obtained with the sugar solution than with the salt solution?
Cook the sirup in sauce pans of the same size and shape. At the tempera-
tures given below remove portions of the sirup. Remove the pan from the stove
when making each test. Drop a tablespoon of the sirup in cold water. Note
the consistency. Is it easily molded? Does it ring when hit against the side of
the container? When do threads or hairs begin to form when a portion of the
sirup is allowed to flow from a spoon? How do the character and length of the
threads vary at different temperatures? Keep the series of tests on your work
tray for comparison w r ith the following experiments and with your neighbors'
results. Note the texture at room temperature. Is it soft, firm, or brittle?
Put a portion in your mouth. Does it dissolve rapidly on the tongue? To
what stage in candy cookery does each of the temperatures given correspond?
LABORATORY OUTLINE
73
Compare with results given in candy and in cook books. Tabulate your
results.
Tempera-
ture
Texture
Threads
Stage of
cookery
Used
for
In
Room
On the
water
temperature
tongue
111
113
118
122
132
145
170
B. Sucrose and corn sirup.
Dissolve YZ cup (100 grams) of sucrose and ^ cup (162 grams) of com-
mercial corn sirup in 1/3 cup of water. Repeat directions under 4A. What is
the effect on the stage of cookery or hardness when one-half sucrose and one-
half corn sirup are used? Compare your results with those of Miss Daniels in
J. Home Econ. 6: 457 and 482 (1914).
Tempera-
ture
Texture
Threads
Stage of
cookery
Used
for
In
Room
On the
water
temperature
tongue
111
113
118
122
132
145
170
C. Sucrose and crystalline dextrose.
Dissolve ]/?. cup (100 grams) of sucrose and //2 cup of crystalline dextrose
(80 grams) in ^ cup of water. Repeat directions under 4A. How does the
hardness of the sirups obtained under 4A, 4B, and 4C compare for any given
definite temperature, for example, 118C. ?
74
SUGAR COOKERY
Tempera-
Texture
ture
Threads
Stage of
cookery
Used
for
C
In
Room
On the
water
temperature
tongue
111
113
118
122
132
145
170
D. Sucrose and dextrin.
Dissolve ]/z cup (100 grams) of sucrose and j/2 cup of dextrin in ^ cup of
water. Repeat directions under 4A.
Tempera-
ture
Texture
Threads
Stage of
cookery
Used
for
In
Room
On the
water
temperature
tongue
111
113
118
122
132
145
170
Results and conclusions.
Suggestions for Variation of Experiments and
Additional Experiments
Repeat Experiment 4C, using one-half sucrose and one-half sorghum. Re-
peat using molasses for the sorghum.
Repeat 4B, using 2 parts of sucrose and 1 part of corn sirup. Repeat using
dextrose for the corn sirup.
TAFFY
75
Repeat 4B, using 1 part of sucrose and 2 parts of corn sirup. Repeat using
dextrose for the corn sirup.
Taffy
Experiment 5.
To determine the conditions necessary for making a pulled candy.
Recipe :
Sugar
Water
1 cup
Yz cup
200 grams
Directions. Combine the ingredients. Cover the pan for the first few minutes
of boiling. Why? Cook to the desired temperature and pour quickly into a
buttered plate. Do not scrape the cooking pan with the spoon. Cool the sirup
until it can be handled without burning the hands. Pull until light in color.
1. Cook to 128C.
2. To the above recipe add 1 teaspoon of cream of tartar.
3. To the recipe add ^4 cup (81 grams) of corn sirup. Should the tempera-
ture to which the sirup is cooked be higher or lower than 128C. ?
4. To the recipe add ^2 cup (162 grams) of corn sirup. Should the tempera-
ture to which the sirup is cooked be higher or lower than 128C.?
5. To the recipe add 1^ tablespoons of vinegar.
6. To the recipe add ^2 cup (162 grams) of sorghum or molasses. To what
temperature should the sirup be cooked?
7. To the recipe add J/ cup of honey (162 grams). To what temperature
should the sirup be cooked?
Is 128C. always the best temperature for pulled candies? Look up recipes
in cook books. What do they contain besides sugar and a liquid? What is the
purpose of the added substances? When the candy has hardened examine a
portion under the microscope. Is the candy crystallized? Save portions of all
candies for several days. Do any crystallize after long standing? Compare
the behavior of this candy with that of sulfur in the crystalline and the amor-
phous condition.
Enumerate all the factors which may cause the relationship between the
cold-water test and a given boiling temperature to vary. What would the re-
sults be if 1 or 2 tablespoons of lemon juice were added to the pulled candy
recipe ?
Temperature
cooked to
Texture
Flavor
Comments
Results and conclusions.
76 SUGAR COOKERY
Caramels
Experiment 6.
Xo determine the conditions necessary for making caramels.
Recipe :
Sugar
2 cups
400 grams
Corn sirup
1 cup
328 grams
Butter
2 tablespoons
28 grams
Milk
3 cups
732 grams
Prepare one-quarter or one-half of the recipe.
1. Combine all the ingredients and stir while cooking to prevent scorching.
Cook to 121C. and turn into a buttered pan very quickly, taking care not to
scrape the contents of the cooking pan with the spoon while pouring the cara-
mel mixture. Do not try to drain the last of the contents of the cooking pan
into the cooling pan. When cool enough, cut into squares with scissors or
a knife.
2. Combine all the ingredients but reserve two-thirds of the milk. Cook
until quite thick, about 119C. ; then add half of the remaining milk so slowly
that the mixture does not stop boiling. Cook until the sirup becomes thick
again; then add the remainder of the milk slowly. When the temperature
reaches 121 C., remove from the fire and follow directions under 1.
3. Repeat 2, but cook to 119C.
4. Repeat 2, but use \ l / 2 cups of sugar and \ l / 2 cups of corn sirup. Cook
to 118C.
5. Follow directions under 2 for combining but use 1 cup of sugar and 2
cups of corn sirup. Cook to 116 to 117C.
6. Substitute 1 cup of sorghum for the corn sirup. To what temperature
does it need to be cooked to have the cold-water test the same firmness as in
3 ? Follow directions under 2 for combining and cook so that the caramels will
be as firm as those under 3.
7. Repeat 6 but substitute strained honey for the sorghum.
8. Substitute 2 cups of cream for the 3 cups of milk. Omit the butter. Follow
directions under 2 for combining. Add % teaspoon salt. Cook to 119C.
9. Reduce the milk to 2 cups and increase the butter to /^ cup. Follow
directions under 2. Cook to 119C.
10. Substitute ^4 CU P of evaporated milk for the 3 cups of milk. Follow
directions under 1. Cook to 119C.
11. Substitute 1 cup of water for the 3 cups of milk. Follow directions
under 1 for combining. Cook to 119C.
12. Add 2 squares of chocolate (56 grams) to the recipe. Follow directions
under 2 for combining. Cook to 119C.
Cold-water test for caramels. The caramels are cooked sufficiently when a
portion of the sirup dropped in cold water is as firm as that wished in the
finished caramel. If small quantities of ingredients are used in making cara-
mels, it is difficult to use a thermometer for the stirring of the viscous sirup
pulls and piles it up against the thermometer. The viscosity of the solution
also seems to have a tendency to hold in for a few seconds some of the steam
FONDANT
77
formed. Thus it is difficult to secure accurate readings, the temperature
fluctuating considerably.
Wrap portions of each of the caramels and store until the following class
period. Do any of them crystallize? Do the larger proportions of corn sirup
keep better? Do any with the small proportions of corn sirup crystallize? When
the proportions of the ingredients of the recipe are changed is the temperature
as indicated by the thermometer or the cold-water test a better indication that
the sirup is the right concentration for removing from the fire? Can smaller
quantities of milk be used?
Temperature
cooked to
Firmness
Texture
Flavor
Color
Results and conclusions.
Fondant
Experiment 7.
To determine the factors which influence the rate of crystallization of
sucrose and the size of the crystals.
Dissolve 1 cup of sucrose (200 grams) in */2 cup of water. (Increase or
decrease these proportions if necessary.) Use pans of the same size and shape.
Be sure the pans are smooth. Because the sirup splashed on the sides dries
less readily from the heat of the burner, a pan with a straight side or one that
curves in at the top is preferable to one that slopes outward at the top.
If desired the sirup may be poured into plates for cooling instead of following
directions under the outline. If this is done the containers into which it is
poured should be smooth and the same size and all should be cooled in the
same manner. Great care should also be taken to pour the sirup rapidly and
not to scrape the pan.
If the amount of water in the fondant is to be determined, the pan and
the stirring spoon should be weighed before the fondant is cooked. The weight
of the fondant, before removal from the cooking pan, minus the weight of the
sugar used gives the amount of water in the fondant.
A. Temperature at which the sirup is beaten.
1. Cook the sirup covered for 4 or 5 minutes. Remove the lid and continue
boiling until sufficiently concentrated. (Cook to 113C. if the day is clear, and
to 114 or 115C. if rainy or if the humidity is high.)
Boil the sirup without stirring or if stirred follow the caution given in the
text. Cool the sirup in the sauce pan to 40C. then beat until stiff. If a wooden
spoon is used for beating it is less likely to form blisters on the hands than a
metal spoon. After crystallization has occurred, knead until soft. Care should
be taken that no crystals form on the side of the pan during cooking or cool-
ing, for they will seed the mass and the time for beating will thus be shorter
for A2 and A3 than would normally be required and the crystals larger.
2. Repeat 1 but cool only to 70C. before beating.
78
SUGAR COOKERY
3. Repeat 1 but beat the sirup as soon as it is removed from the stove.
Examine portions of each fondant under the microscope. Wrap portions from
each experiment in oiled paper and put away in a tightly covered container until
the next lesson. What is the effect of 24 hours' storage on the firmness and
the texture of the fondant? Why do the directions under Al state not to stir
the sirup while cooking?
Temperature
cooked to
Temperature
cooled to
Time required to beat
to crystallize
Size of crystals
Results and conclusions.
B. Concentration to which the sirup is cooked.
Repeat Al, but cook the sirup to 111C. Compare the length of time re-
quired to beat to crystallize with that for A3.
C. Effect of added substances.
1. Repeat Al, but add 1 tablespoon of butter to the sugar and water.
Follow directions under Al.
2. Repeat Al, but add ]/$ teaspoon of cream of tartar to the recipe. The
proportion of cream of tartar may need to be varied somewhat with the
hardness of the water, but the rate of cooking will have more effect than
the hardness of the water. Boil over a large gas burner so that the time of
cooking does not exceed 10 to 12 minutes. Follow directions under Al.
3. Repeat C2, but cook slowly, taking at least 2 or 3 times as long to cook
as for C2.
4. Repeat Al, but add 1 teaspoon of cream of tartar to the recipe.
5. Repeat Al, adding 1 tablespoon of corn sirup to the recipe.
6. Repeat Al, adding 4 tablespoons of corn sirup to the recipe.
7. Melt 4 tablespoons of sugar. Stir while melting. Do not have the heat
intense enough to decidedly darken or scorch the sirup. When it is all melted
and a golden brown color, add boiling water and stir until dissolved. Then
add to the fondant recipe and follow directions under Cl.
Sugar
grams
Water
grams
Added
substance
Cook to
c.
Cool to
c.
Time required to
cook to reach
113C.
Time required to
Amount
beat to
of water in
Color
Texture
Flavor
Yield
crystallize
fondant
FUDGE 79
If C4, 6, and 7 do not crystallize let them stand until the next lesson.
What would be the effect on the rate of crystallization if these candies were
allowed to cook to a higher temperature? If they were beaten hot? What is
the effect on the rate of crystallization of sugar when considerable hydrolysis
has occurred, as in C3 and C4, or when a large amount of corn sirup or
caramelized sugar has been added, as in C6 or C7?
Test portions of Al and C2 with Fehling's solution.
What is the action of cream of tartar when added to fondant? What
would be the result if vinegar or lemon juice were substituted for the cream
of tartar in C2 and C3 ? Is the fondant obtained in C2 and C3 superior to
that obtained in Al ? Compare the keeping qualities of the different fondants
by putting some of each away in a covered container and observing at
different periods. Examine portions of each under the microscope.
Experiment 8.
To determine the comparative ease of crystallization of different sugars
in making fondant.
A. Repeat Experiment 7A, but substitute dextrose for the sucrose.
B. Repeat Experiment 7A, substituting levulose for the sucrose. If levu-
lose cannot be obtained use honey, which contains a high percentage of
levulose. Or use the liquid portion of crystallized honey, which is nearly
pure levulose.
If any under A or B do not crystallize, recook them. See if they will
crystallize after being cooked to a higher temperature.
Fudge
Experiment 9.
To determine the factors influencing the consistency and flavor of fudge.
Recipe :
Sugar 1 cup 200 grams
Milk ]/2 cup 122 grams
Butter 1 tablespoon 14 grams
Chocolate ^ square 21 grams
Combine sugar, chocolate, butter, and liquid. Stir until the sugar is dis-
solved and the chocolate is melted. Cook to the temperatures given below.
If the mixture is poured into another container for cooling, be sure the con-
tainer is smooth. If it is poured into a platter or similar utensil, cooling will
be more rapid and even more so if the platter is set on a cake rack or is ele-
vated. Use containers of the same size and the same method for all the
experiments. Cool to 40 C. and beat until the mass begins to crystallize.
Turn quickly into a buttered pan or knead as desired. Select thermometers
that have the same boiling point. The recipe may need to be doubled or
increased so that the quantity of material in the cooking pan will be great
enough to cover the bulb of the thermometer in order to obtain an accurate
reading. How should the thermometers be held in the sirup to determine
SUGAR COOKERY
differences in consistency of the finished fudge, when the difference in tem-
perature to which the sirup is cooked is only 1 degree?
Compare the texture and consistency of each fudge. What temperature is
most desirable for fudge that is not kneaded? For fudge which is kneaded? If
granular fudge is desired and the sirup is stirred while hot, should the sirup be
cooked to the same degree as for fudge that is beaten after cooling? In making
4 times the recipe would you take 4 times the quantity of liquid? Why?
A. Temperature to which the sirup is cooked.
Temperature
cooked to
Time required to beat to
crystallize
Texture
Consistency
1. 110C.
2. Ill
3. 112
4. 113
5. 115
Results.
B. Kind of liquid.
Cook to the temperature found best under 9A.
1. Use water for the liquid.
2. Use milk for the liquid.
3. Use cream for the liquid.
4. Use cream for the liquid and omit the butter.
C. Time of adding the fat.
1. Add fat at first so that it is in the sirup during the cooking process.
2. Add fat after removing from the fire. Put fat on top of hot fudge, but do
not stir until cool enough to beat. Compare flavor and texture with the fudge
under Cl.
D. The proportion of cocoa used.
The thermometers should have the same boiling point and all conditions
should be carefully standardized. Follow directions under A.
1. Substitute 1 tablespoon (7 grams) cocoa for the chocolate. Cook to 114C.
2. Substitute 2 tablespoons (14 grams) cocoa for the chocolate. Cook to
113C.
3. Substitute 3 tablespoons (21 grams) cocoa for the chocolate. Cook to
1.12C.
4. Substitute 4 tablespoons (28 grams) cocoa for the chocolate. Cook to
111C.
5. Substitute 5 tablespoons (35 grams) cocoa for the chocolate. Cook to
110C.
If Dl is too hard repeat the series cooking Dl to 113C. and decreasing
the temperature 0.5 for each tablespoon of cocoa added. Place portions of the
fudges away to ripen. Compare texture and flavor. Which proportion of cocoa
do you prefer?
ADDITIONAL EXPERIMENTS 81
Write a summary of the factors that influence the flavor and consistency
of fudge.
Suggestions for Variations o Experiments or Additional
Experiments with Fudge
Prepare fudge by adding 1 tablespoon of corn sirup to the recipe.
Prepare fudge by adding 2 tablespoons of corn sirup to the recipe. Compare
flavor, texture, glossiness, and keeping qualities with fudges made under Ex-
periment 9.
Prepare fudge by adding fondant to the fudge.
Experiment 10.
To determine the effect of a weak alkali and heat upon crystalline dextrose
when it is used in fondant.
Recipe :
Crystalline dextrose 1 cup
Water Ys cup
1. Use distilled water and cook until a medium firm ball is formed in cold
water. Cool to 50C. and beat.
2. Repeat 1, but substitute hard water for the distilled water.
3. Use 20 per cent, or 1/5 cup, of dextrose, and 80 per cent, or 4/5 cup, of
sucrose. Use distilled water and cook until a soft ball is formed in cold water.
What is the temperature? Cool to 50C. and beat.
4. Repeat 3, but substitute hard water for the distilled water.
5. Repeat 3, but add 200 parts of magnesium carbonate per million parts
of water to the recipe. (This is less than the proportions of carbonates found
in much of the water used in different sections of the country.)
6. Repeat 3, but add 1/64 teaspoon of soda to the recipe.
7. Repeat 3, but add 1 tablespoon of vinegar or lemon juice to the recipe.
Cream of tartar, % teaspoon, may be used for the vinegar or lemon juice.
The main principles of sugar cookery are covered, and some are repeated,
in the preceding experiments. Some frostings and some candies have added
substances, like egg white, which retard crystallization. The principles for
cooking are the same as those used in cooking and preparing the candies of
the preceding experiments. However, to have frostings a consistency to
spread and cut well, variations in temperature of cooking from that of
candy may be necessary.
Suggestions for Additional Experiments
1. Prepare chocolate fudge icing and use on cake or cookies. Determine the
temperature to which the sirup should be cooked.
2. Substitute brown sugar for white sugar in icing.
3. Make caramel or burnt-sugar icing by melting one-half the sugar to be
used to a golden brown color. Then dissolve in water. Add the remainder of
82 SUGAR COOKERY
the sugar, and the butter, and cook to the same temperatures used for choco-
late fudge icing. Which temperature produces the best texture of icing?
4. Prepare boiled icing by pouring the cooked sirup over beaten egg white.
Prepare an outline for making this type of icing, giving variations in tem-
perature to which the sirup is cooked before adding to the egg white and the
temperature to which the sirup is cooled before adding the sirup to the egg
white. Vary the amount of sugar used for different proportions of egg. Consult
any reference that you wish for making your outline and use the results of any
of the sugar experiments.
For a control use 1 cup sugar, 200 grams, ^4 CU P corn sirup, 82 grams, and
l /4 cup of water. Cook to 119 or 120C. and pour slowly into 1 stiffly beaten
egg white, beating as the sirup is added. For divinity beat until pieces dropped
on wax paper will hold their shape.
CHAPTER III
FREEZING
A pure liquid has a definite freezing point. In freezing the fluid
changes from a liquid to a solid state. Water freezes at 0C. or 32F.
Just as sugar solutions in cooling may give supersaturated solutions before
crystallization starts, so water may be supercooled before it freezes.
Furthermore, the conditions for supersaturation and supercooling are
similar. For supersaturation the solution must not be agitated and no
crystals must be added. If a test tube of water containing a thermometer
is immersed in a mixture of ice and salt, the temperature of the water will
drop to 4C. or lower. If the slightest movement is made or if a small
crystal of ice is added the water will crystallize quickly, and the tempera-
ture rises to 0C., for water in freezing gives off heat. A gram of water
changing from to ice at 0C. gives off 79.9 (or about 80) calories of
heat. When the water has been supercooled, this heat of solidification
elevates the temperature of the ice and liquid to 0C. The heat of crystal-
lization may be absorbed by the liquid or given off to the surroundings if
the freezing liquid is not insulated.
The Freezing Point of a Liquid
The freezing point of a liquid cannot be defined as the temperature at
which the liquid becomes a solid, for supercooled liquids are cooled below
the freezing point. The freezing point and the melting point are identical,
so that the freezing point may be defined as the temperature at which the
solid melts. The freezing point of a liquid may also be defined as the
temperature at which the solid and liquid are in equilibrium. Here equilib-
rium means the temperature at which any proportion of solid and liquid
can exist without change, that is, no solid melts and no liquid freezes.
For water, this temperature is 0C. Of course, equilibrium can exist for
a long period of time only if the solid and liquid are completely insulated
or if the temperature of the surroundings is at the freezing point of the
liquid. If the temperature of the surroundings changes slightly above 0C.
so that heat is absorbed, some of the solid melts. If the temperature of
the surroundings is below 0C, so that heat is withdrawn from the mix-
ture, the liquid freezes. After all the liquid is frozen, the temperature
of the ice may drop below 0C., just as the temperature of the ground or
a stone may assume the temperature of the surroundings.
83
84 FREEZING
If ice and water that are not at the same temperature are mixed, they
are not in equilibrium, since ice and water are in equilibrium only at the
freezing point or 0C. If the temperature of the ice is 0C. and the
temperature of the water is 20C. some of the ice melts. In melting, each
gram of ice absorbs 80 calories of heat, and the temperature of the water
is lowered. If sufficient ice is added to the water, and the temperature
of the surroundings does not influence the mixture, ice melts until the
temperature of the water reaches 0C. and equilibrium is established. If
the quantity of ice added to the water is not sufficient to lower the
temperature of the water to 0C., the temperature of the water is lowered
as long as the ice melts and provided the surroundings do not influence
the temperature. After the ice is all melted the temperature of the water
cannot be lowered except from the surroundings.
Lowering of the Freezing Point
When a soluble substance is dissolved in a liquid the freezing point is
lower than that of the pure solvent. A gram-molecular weight (mole)
of a non-ionized substance in a liter of water lowers the freezing point
1.86C. The lowering of the freezing point can be continued as long as
the substance is soluble. If no more than 3 moles of a non-ionized substance
are soluble in a liter of water, the freezing point cannot be depressed
below 5.58C. Substances that are not very soluble do not affect the
freezing point particularly, because such a small portion of a mole of the
substance is dissolved. Thus substances in suspension, such as fat in milk
or cream, do not affect the freezing point of an ice-cream mix in the same
way that sugar does, for the fat is not soluble.
Ionized substances and the freezing point. Sugar does not ionize
or dissociate in the solution to an extent great enough to influence the
freezing point. Salt belongs to the groups of electrolytes' which dissociate
into ions in the solution. The amount of ionization depends upon the
concentration of the solution : the less concentrated the solution the greater
the dissociation. In a very dilute solution, complete dissociation into ions
may occur. If 58 grams of salt or sodium chloride in 1 liter of water
are completely ionized into sodium and chlorine ions, there will be 1 mole
of sodium ions and 1 of chlorine ions. Thus the two lower the freezing
point (2 X 1.86) or 3.72C. The molecular weight of sucrose is 342
grams, that of levulose is 180, and that of dextrose is 180 grams. None of
the sugars ionize to an extent that affects the freezing point. Compare
the freezing points, if 1/4 cup, or 150' grams, each, of sucrose, levulose, or
dextrose is added to a quart of cream.
Calcium chloride ionizes into 3 ions. Therefore, a mole of calcium
chloride depresses the freezing point more than a mole of sodium chloride.
FREEZING MIXTURES 85
The calcium chloride is also more soluble than sodium chloride, so that a
greater number of moles can be dissolved in a liter of water.
CaCl 2 < > Ca++2Cl-
The Freezing Point of Ice Cream and Ices
Milk, which contains sugar and other dissolved substances, has a lower
freezing point than water. When sugar is dissolved in water and some
fruit juice added to make a sherbet or ice the freezing point of the sherbet
mixture is about 4 to 5C., depending upon the proportion of sugar
added. Ice cream containing about Y^ cup of sugar to a quart of cream
freezes between 1 and 2C., or about 29F. Ice cream usually con-
tains a smaller percentage of sugar than ices or sherbets,
Freezing Mixtures
When a crystalline substance is added to a liquid its freezing point is
lowered. However, as a solution freezes it separates into crystals of the
solvent and crystals of the dissolved substance.
Suppose 10 grams of salt are added to 90 grams of water to give a 10
per cent salt solution. The salt dissolves and the temperature of the solu-
tion is lowered. The freezing point of salt solutions may be shown in
the diagram by the line AB. The temperature is represented vertically
and the percentage of salt in the solution is represented horizontally.
The freezing point of water is 0C. This is represented on the line
AB of Fig. 13, at A. The freezing point of a 10 per cent salt solution
is about 5C. This is shown at point X, where the freezing-point line
AB cuts the line indicating a 10 per cent salt solution. If the salt solution
is cooled to 5C. some of the water freezes. This leaves a greater con-
centration of salt than 10 per cent in the rest of the solution. Thus the
freezing point of the rest of the solution is lowered. If cooling of the
solution is continued, ice will continue to form, and the remaining salt
solution will become more concentrated and its freezing point lower. The
lowering of the freezing point can be continued until the line AB cuts
the line BC. The point B represents the limit of the solubility of the
salt at a temperature of 22C. Below this temperature the salt and
water separate, both crystallizing. This is called the cryohydric point.
Both the ice and salt may be cooled to lower temperatures than 22C.
after they are in solid form.
If salt is mixed with water a saturated solution is obtained when the
solution contains 35.6 grams of salt per 100 grams of solution at 0C.
If this solution is cooled below 0C. the solubility of the salt is not so
great at the lower temperatures. This is shown on the line CB. A little
below 0C. salt combines with 2 molecules of water. Thus the slope of the
86
FREEZING
curve for solubility of salt changes below 0C., and the salt is found in
solution as the dihydrate. If a saturated salt solution is cooled below 0C.
the excess salt beyond saturation point is precipitated from solution. This
will continue until the cryohydric point is reached.
Salt is often added to ice for a freezing mixture. When salt is added
to water and ice at 0C. they are not in equilibrium, even if the sur-
roundings are at 0C., for the addition of salt lowers the freezing point
of the solution. Since they are not in equilibrium the ice melts and the salt
dissolves in the water. There is always a film of water on the surface
of the ice. As the salt dissolves in this small amount of water it absorbs
heat. This absorbed heat is taken from the brine or from the surround-
4?
s
Q.
1-20
-30
10
20
30
40
Per Cent NaCI
FIG. 13. The freezing point of solutions containing different percentages of
sodium chloride and the solubility of sodium chloride below 0C.
ings. If the heat is taken from the brine the temperature of the brine
is lowered.
When salt is added to ice, one of three things may happen, depending
upon the proportion of ice and salt, and the surrounding temperature or
insulation. All the salt may be dissolved. When this happens the melting
of the ice lessens the concentration of the salt solution and the tempera-
ture is not lowered beyond the point obtained when the solution con-
tains the highest concentration of salt. All the ice may melt. When the ice
is melted the temperature cannot be lowered to a greater extent, for
there is no more ice to melt to absorb the heat. The cryohydric point may
be reached. At this point the solution becomes solid and separates into
ice and salt.
Ice-cream freezers. An ice-and-salt mixture is used to lower the
temperature of other substances. An ice-cream freezer is a utensil made
to freeze a substance placed in a center metal container. Outside this metal
TWO PROCEDURES USED IN FREEZING 87
container there is a space in which the cooling medium is placed. The outer
wall of the ice-cream freezer is often of wood, which is a poor conductor
of heat. Since it conducts heat slowly it partially insulates the ice and
salt from the surrounding air. The freezing mixture absorbs heat. In
doing this it lowers the temperature of the brine and removes heat from
the contents of the center can. In order to freeze the contents of the can
the temperature of the brine formed must be lower than the freezing point
of the mixture to be frozen.
To freeze the contents of the ice-cream can, considerable heat must be
removed from it. As a result, a corresponding amount of ice must melt to
absorb the heat. Therefore, the contents of the can do not begin to freeze
until considerable brine has formed. Conduction of heat is more rapid by
water than by air. Before the brine forms and replaces the air spaces around
the ice, conduction of heat from the can is slow. After all the salt is dis-
solved or all the ice is melted, the temperature of the brine cannot be
lowered, unless the temperature of the surrounding air is lower than the
temperature of the brine. In ice-cream making the temperature of the sur-
roundings is usually much higher than the temperature of the brine.
When the quantity of ice left in the freezer is small the temperature of the
surrounding air may heat the brine more than the melting of the small
amount of ice cools it. Before this stage is reached the freezer needs fresh
ice and salt packed around it.
The lowest temperature obtainable for a brine from a salt and ice mix-
ture is about 22C. (Walker reports 21 and Bigelow 22.4C.)
This temperature is called the cryohydric point. If calcium chloride is
used with ice the lowest temperature obtainable is 55 C.
At the cryohydric point 29 parts of salt are soluble in 71 parts of water.
No more salt can be dissolved at this temperature. This proportion of salt
to ice is about 1 to 3 and is often used in freezing mixtures.
Ice in the refrigerator is probably about 0C., but ice from out of
doors on a cold winter day may have a temperature far below 0C. When
ice at a very low temperature is used for freezing, a brine will form more
quickly and freezing start sooner if water is poured over the ice and salt.
Proportion of Ice and Salt for Freezing and Packing
Rate at which the temperature is lowered. The rate at which the
temperature of the brine and thus also that of the mix to be frozen is
lowered depends on the proportion of ice and salt, and on the fineness
of division of the ice and salt. Small pieces of ice provide greater surface
and thus melt faster than large pieces. Fine salt dissolves more quickly than
coarse salt, but a fine table salt is likely to lump. Crushed rock salt is good
to use.
Two procedures are used in freezing. The smooth, velvety texture
of ice cream and ices depends on several factors. One important factor is
88 FREEZING
the size of the crystals formed. The proportion of ingredients, their treat-
ment, and the incorporation of air bubbles into the mixture while it is
freezing are also important. Small crystals may be obtained by the quick-
freezing method. A very low temperature is used, the mass being frozen
so rapidly that many nuclei are formed and there is little crystal grow T th
because of the short time. This process is easier to use commercially than
in the home, because of the very low temperature employed for freezing.
Judging from reports in the ice-cream trade journals, it is successful in
some instances and not in others.
The other procedure is to freeze at a slower rate, depending on agita-
tion to form many nuclei. Air is incorporated in the mix in both processes.
A temperature of 8 to 10C. is sufficiently low to freeze most ice
creams, sherbets, and ices. For home freezing, 1 part of salt to 8 of ice
is a good proportion. Commercially, 1 part of salt to 12 of ice is often
used. Washburn states that a proportion of 1 part of salt to 40 parts of ice
will freeze if given ample time. The air globules are retained in the mixture
better after it has nearly reached the freezing point. The air is beaten
in by the dasher paddles. In freezing very rapidly there is not time to
incorporate as much air as when the mix is frozen at a somewhat slower
rate.
Packing the freezer. Commercially most ice cream is now held in
mechanically operated freezing units or rooms, although the same propor-
tions of ice and salt may be used for packing that are used for freezing.
For home-made ice cream the same proportion of ice and salt may be used
as for home freezing, or about 1 of salt to 8 of ice. In packing, the ice
should be pressed down tight in the can. This will force the surplus water
out of the opening in the container. If the water is drained off it only takes
a longer time for the brine to form again, and cooling is slower. A little salt
should be added to the ice left in the freezer before the new ice is added.
For home-made ice cream that is hot to stand very long before serving, a
larger quantity of salt may be used to advantage. This will cause the
temperature to drop quickly and hardening of the cream w T ill take place
more rapidly.
The ice and salt may be mixed together before putting in the freezer,
but a better way of packing is to fill the freezer half full of ice, then
add a layer of salt. The ice and salt are then added in alternate layers until
the top is reached. The water from the melting ice \vashes the salt towards
the bottom of the freezer, and once it reaches the bottom it is of small
use for cooling purposes. Therefore, it is preferable to pack the freezer
with the salt towards the top.
Mousse. For packing home-made mousse, the proportion of salt to
ice must be large, 1 to 3 or even 1 to 2. Whipped cream which has air
beaten into it is added to a mousse. The mousse is molded and often is not
stirred while freezing, although it may be stirred very slowly. Heat or
cold penetrates more slowly to the center of a mixture that is not stirred.
FAT 89
In addition, the air and the high fat content of the whipped cream are
poor conductors of heat and cold. Thus a mousse requires a low tempera-
ture and long time to cool. The ice and salt may need to be repacked
unless set where the air is cold.
The Composition of Ice Cream
A simple home-made ice cream may be made with cream, sugar, and
flavoring. Flavoring is added to increase the palatability. The flavoring may
be extracts, fruit, or nuts. Sometimes egg is added to home-made ice cream.
Cream containing 17 to 20 per cent butter fat, or if not homogenized,
22 per cent fat, gives a good home-made ice cream. Washburn states that
the weight of sugar added may be one-sixth of the weight of the cream.
Three-fourths of a cup of sugar to a quart of cream gives about this
proportion, and this produces an average sweetness. The serum solids
usually average about 6 per cent in home-made ice cream.
Sommer states that a good commercial ice cream is obtained with the
following proportions :
Fat
12.5%
Serum solids
10.0
Sugar
16.0
Gelatin
0.25 to
0.50
Egg yolk solids
0.50
Total solids 39 . 25 to 39 . 50%
Sommer also states that a richer ice cream has not proved generally
successful because of the higher cost, but is preferred by many consumers.
In the richer cream the fat is increased to 16 per cent and the serum solids
reduced to 8 per cent. Although Sommer recommends the egg yolk solids,
many manufacturers omit them. Gelatin, called a binder, is used to prevent
coarse crystallization. Commercial ice cream must have condensed-milk or
dry-milk products added to raise the serum solids to 8 or 10 per cent.
The milk solids include the butter fat, the milk proteins, the milk sugar,
and the ash; serum solids exclude the fat; total solids of ice cream include
the milk solids and the added sugar. The total solids vary, but Sommer
states they should not exceed 41 per cent. Each of the ingredients of the
milk and also the added sugar has an effect on the body and the texture
of the ice cream. The ingredients likewise affect the flavor.
The Flavor of the Ice Cream
Fat. The flavor of the ice cream is influenced by the ingredients that
go into it. They should be free of foreign odors and flavors. Ambrose states
that "increase in butter fat gives the richness of flavor that can be ob-
tained in no other way."
90 FREEZING
Williams and Campbell conducted experiments in ice-cream making in
which the fat content was varied: creams were made with 12, 15, and
18 per cent fat, the other constituents remaining the same, and the method
of making being kept uniform in each experiment. Purchasers were al-
lowed to sample the three ice creams on the first day and on the following
day could purchase their choice. The records showed that 80 per cent
of the purchasers favored the ice cream containing 18 per cent fat, 10.4
per cent favored the ice cream containing 15 per cent fat, and 7.6 per cent
of the purchasers favored the ice cream containing 12 per cent fat.
Salt. Salt may be added to ice cream, and for some persons the flavor is
thereby improved. It is so easy to add too much that it is often better to
omit it. A good proportion to use is about ^2 teaspoon of salt per gallon
of mixture.
Acidity. Acidity of the cream affects the flavor. The acidity of milk
and cream increases with age. An acidity of 0.30 per cent produces an
apparent sour taste; that usually preferred for ice cream is from 0.16 to
0.20 per cent.
Sugar. Williams and Campbell in experiments with ice cream, con-
ducted like those just referred to with the fat, but in which the percentage
of sugar varied, found that 61.4, 28.4, and 10.2 per cent of the purchasers
showed a preference for the 19, 16, and 13 per cent sugar, respectively.
This gives a total of 90 per cent favoring the ice cream with 16 or more
per cent of sugar.
Serum solids not fat. Similar experiments with serum solids not fat
showed that 55.6, 25, and 18.6 per cent of the purchasers favored the ice
cream containing 12, 9, and 6 per cent of serum solids, respectively.
In regard to gelatin, 63.2, 13.8, and 23 per cent of the purchasers
favored the ice cream containing 1, 0.5, and per cent of gelatin, respec-
tively.
Fisher states that the serum solids do not affect the flavor until a content
of 12 per cent and beyond is reached. To obtain this amount of serum
solids, condensed-milk or dry-milk products must be used. With 12 per
cent or greater a condensed-milk flavor is imparted to the ice cream. Fisher
also states that butter fat improves the flavor slowly.
Sandy ice cream. When too great an amount of condensed milk is
added, there is danger of the lactose crystallizing at the low temperatures
in the holding room. When the lactose crystallizes, a sandy or gritty tex-
ture is imparted to the ice cream. Such ice cream is called sandy. Leighton
and Peter have reported that lactose does not usually give sandiness to the
ice cream unless the concentration of serum solids is high, i.e., about
12 per cent or more. The lactose may crystallize in the ice cream when the
percentage of lactose is 6 per cent or more.
Flavoring. Flavoring is added to the ice cream. Too little flavoring
to blend with the cream and sugar gives a flat taste; too much makes the
flavoring the only ingredient evident to the taste. Dahle states that "Noth-
INCORPORATING CHOCOLATE OR FRUIT 91
ing is to be gained by the use of cheap flavors." Crushed fruit, fruit juices,
and nuts are also used to flavor ice cream.
The Body and Texture of Ice Cream
By body, the whole mass of ice cream is referred to its firmness,
its resistance; texture refers to the finer particles of the ice cream.
Effect of fat on texture. High butter fat produces a firm body, for
the chilled fat particles are very firm. Too much fat produces a very hard
ice cream. Fillers are sometimes used to give a better body. In home-made
ice cream when little cream is used, egg may be added to produce a firmer
body, and to add flavor.
Effect of proteins on texture. The milk solids not fat and the
protein content particularly affect the body of the ice cream. The casein
and albumin of milk are found as calcium and magnesium caseinates and
albuminates in the milk. As such they imbibe water and swell. With too
little protein the body has little resistance, and with too much protein its
hydration produces a very soggy, heavy ice cream. Mortensen states that
high serum solids give a smooth mix for they absorb the water, but
their use can be carried to an extreme. He adds that those who do not
use a high percentage of serum solids must pay more attention to the
treatment of the mix. Combs and Martin concluded that a certain amount
of acidity produces a finished appearance in the mix. They have found that
too high acidity causes the ice cream to melt quickly, since the reaction is
brought nearer the isoelectric point of casein and at the isoelectric point
very little water is held by casein.
Effect of treatment of the mix on texture. Any treatment of the
ingredients of the ice cream or of the mix itself that increases the viscosity
affects the body and texture of the ice cream. Pasteurization, homogeniza-
tion, and aging all affect the viscosity and will be discussed later. Though
the texture of the ice cream, like the body, is affected by the ingredients
used and their proportions, it is also affected to a greater extent than the
body by the freezing process. The texture of ice cream depends largely
on the size of the crystals and the amount of air incorporated during
freezing.
Incorporating chocolate or fruit. Some special problem studies have
indicated that the temperature at which the chocolate is combined with the
other ingredients is the most important factor in obtaining a uniform color
and not a speckled product. The temperature at which the chocolate is
combined, at least with a portion of the ingredients, should be above the
melting point of the chocolate. The chocolate may be added to a portion
of the milk which has been warmed or made into a sirup. Martin advises
that the chocolate be made into a sirup with the sugar and a portion of
the milk.
92 FREEZING
Fruit, such as strawberries, raspberries, and peaches, may be put through
a sieve before adding to the mix. If larger pieces of fruit are desired, they
can be prevented from freezing into chunks of ice by letting them stand
for some time, or over night, in a heavy sirup. The sugar entering the
berries or fruit lowers the freezing point of the fruit, so that it does not
freeze or is less hard. To keep the fruit as whole as possible, the sirup
should be added to the cream mix. Then the fruit is added after the cream
is in a soft frozen state.
The freezing process. If the ice-cream mix has not been cooled
before it is put in the freezer it is better to turn the freezer slowly until
the mix is cooled. If the freezer is turned rapidly while the mix is at a
temperature above 4.5 C. or 40F. the butter fat is clumped together and
a buttery product results. If carried far enough, butter may even be
churned in the mix. The mix does not hold the air incorporated in it until
its temperature is cooled to about 1C. or 34F., so that rapid turning is
of no advantage from this standpoint until the mix is cooled. With a
freezer turned by hand, if the freezer is turned rapidly all the time, one's
energy is often expended before the freezing is finished, and it is during
the latter part of the freezing period that the turning should be rapid. The
size of the crystals formed during freezing depends upon the rate of turn-
ing of the freezer and the length of time of the freezing process. Stirring
the solution during crystallization increases the number of nuclei formed,
and the resulting crystals are smaller than if the mixture is not stirred.
If the ice cream is not stirred during freezing, few nuclei are formed, the
water crystals join onto each other, and a product with very coarse, large,
spiny crystals is the result. On the other hand, if the ice cream is stirred
the size of the crystals depends upon the rate of turning. Very slow turn-
ing while freezing is in progress results in larger crystals; rapid turning
results in smaller crystals. If the freezer is turned very slowly the crystals
build onto the crystals already formed ; with rapid turning many new
crystals are developed. The time of the freezing process also affects the
size of the crystals. If the crystals are formed very rapidly, too little air is
mixed with the cream, which produces an ice cream without a velvety
texture. Since rapid freezing occurs with low temperatures it is better not
to have the temperature of the brine too low, thus 1 part of salt to 8 parts
of ice produces good results.
Overrun. The addition of air to the ice cream during freezing causes
it to swell so that the ice cream increases in bulk. This increase is known
as the swell or overrun.
This swell or overrun due to the incorporation of air particles gives a
smoother, more velvety texture to the ice cream. Mortensen states that it is
preferable to have the air cells in the finished cream small, for the strength
of the film of a small air cell is stronger than that of a large one. To
obtain small air cells in the ice cream the mix should be viscid. A viscid
PERCENTAGE OVERRUN
93
substance resists incorporation of air, and it will be worked in in finer
divided portions. With increased viscosity the air is held in the mix better
after it is incorporated. Mortensen includes homogenization as an impor-
tant factor in increasing the viscosity of the ice-cream mix.
As the swell in freezing improves the texture, it is desirable to obtain
it in home-made ice cream. In the home-made ice cream the freezer is
often filled so full that there is no room for overrun and no air is beaten
into the ice cream during freezing. Filling the freezer two-thirds to three-
fourths full gives good results for home-made ice cream. In home freezing
the overrun obtained is seldom as great as with commercial ice creams,
for the freezing conditions in the home are not controlled so carefully as
in the factory.
Too great an overrun produces an ice cream of poor body and quality,
for it becomes very frothy and foamy. An overrun of 50 per cent is con-
sidered to give a desirable texture.
Percentage overrun. The percentage of overrun depends upon the
speed of freezing and rate of turning.
TABLE 12
EFFECT OF THE SPEED OF THE MACHINE ON OVERRUN (Baer)
Overrun
Time of freezing
Revolutions per
minute
Lot I
Lot II
Lot I
Lot II
50
25
33
10
11
50
28
33
11
10
50
25
35
9
12
150
48
43
7
7
150
48
39
8
5
150
50
40
7.5
6
175
45
58
7
6
175
50
50
7.5
6.5
175
52
55
8
6
The above table, from Baer's results, shows the effects of the speed of
the machine on the overrun. He concluded that 50 revolutions per minute
were too slow, as the overrun was too low, the texture of the ice cream
was coarse, and the body weak and spiny.
From the table it will also be noted that increasing the speed of the
freezer shortens the freezing time. The first crystals are formed at the
edge of the ice-cream mix and against the side of the metal container.
The faster speed of turning keeps these crystals scraped away and brings
warmer portions of the mix against the can to be frozen. In this way the
94 FREEZING
whole mass is chilled and frozen more rapidly than it would be if the
mix were not stirred.
For home freezing it is probably better to over-freeze a little but not
too much, if the ice cream is to be served soon after it is frozen. After
stirring is stopped the rate of cooling is slower. Therefore it requires a
period of standing after the freezing process is completed for the ice
cream to harden suitably for serving. Increasing the quantity of salt for
packing also increases the rate at which the ice cream hardens.
The Factors Affecting the Viscosity of Cream
and Ice Cream
Aging. Sherwood and Smallfield have reported that in some cases
aging shows an increase in viscosity of the cream whereas in others it does
not. When the viscosity is increased the fat globules are larger and clump.
They have found that agitation of the cream reduces the size of the fat
globules and the viscosity of the cream. Mortensen states that cream
just separated from fresh milk should be aged 24 hours before it is used
in ice cream, even if it is not pasteurized. Aging also gives a cream that
whips better. The viscosity of a cream increases noticeably for about 6
hours after it is separated and then increases at a slower rate.
Homogenization. Williams lists the benefits of homogenization, as
applied to ice cream, under 6 heads as follows:
1. Increased viscosity.
2. Reduction in time required for aging.
3. Less physical and mechanical loss of fat.
4. Better whipping qualities.
5. Better freezing qualities.
6. Greater uniformity and palatability.
Ice cream made from homogenized cream is smoother and has smaller
crystals. In homogenization of the cream the fat globules are broken up.
As the size of the globules is decreased the surface area increases. The
fat globules are surrounded by a film of protein. After homogenization,
owing to the increased surface, a larger amount of protein is held in the
film around the fat particles. The increase in the number of the fat globules
and the protein held in the film increases the viscosity of the cream.
After homogenization the cream should not be agitated. The higher the
pressure used during homogenization, the greater the viscosity obtained in
the cream.
With homogenized cream, less fat and less milk solids not fat can be used
and a texture obtained that is as good as that from an unhomogenized
cream with higher fat content and with higher milk solids.
Pasteurization. Pasteurization decreases the viscosity of the cream.
Cream needs to be aged after pasteurization before it is used in ice cream.
HOME-MADE ICES AND SHERBETS 95
The Use of Gelatin in Ice Cream
Gelatin is used in ice cream to prevent the formation of coarse crystals,
during softening and hardening of ice cream packed in an ice-and-salt
mixture, while it is held for selling. Holdway and Reynolds have demon-
strated that gelatin in ice cream prevents it from losing its shape while it
is melting.
Sugar in Ice Cream
Sugar is used for sweetening the ice cream. It increases the total solids,
thus improving the body. Too high a percentage lowers the overrun and
gives an ice cream that is too sweet.
Sucrose is used in ice cream. Other sugars may be used, such as invert
sugar from sucrose, corn sugar, and levulose. Since the commercial levulose
is too expensive, honey may be used. Corn sugar or dextrose is not so sweet
as sucrose and therefore can be substituted successfully for only about 25
to 35 per cent of the sucrose in ice cream.
Making Ice Cream in Refrigerators at Home
Ice cream may be held as well as frozen in mechanical refrigerators.
When frozen in them the ice cream often does not have a good texture
because it is not stirred sufficiently during the freezing process. Some units
have been made that stir the mixture while it is freezing but they are not
common. However, quite acceptable ices, sherbets, and even ice cream may
be made by adding substances, such as egg white or whipped cream, that
tend to delay crystal growth. Beaten egg white is best for ices and sherbets,
because this product is more typical of an ice or sherbet texture than the
product formed by adding rich whipped cream. A good time to add the
beaten egg white to ices is just as the mixture starts to freeze, for the
stirring at this time aids in the formation of more nuclei. Whipped cream
may be added before or after the mixture is placed in the refrigerator tray,
depending on the type of product to which it is added.
Ice-Cream Improvers
The published results of Isenberg and Baer, on the use of ice-cream
improvers in commercial products, indicates that they would be of prac-
tically no benefit in home-made ice cream.
Home-Made Ices and Sherbets
Ices and sherbets have a lower freezing point than ice cream, for they
usually contain a greater quantity of sugar. The use of gelatin and egg
96 FREEZING
white in home-made ices seems to improve the texture in some instances,
but in others to have little effect. When the hot sirup is poured over the
beaten egg white the results obtained are as good as when the beaten egg
white is added during the freezing process.
The sherbets in which milk and fruit juices are combined give delightful-
flavored products for home freezing.
Classification of Ice Creams
Various classifications of frozen products have been proposed. Sommer
gives the following classification of ice cream and related frozen products :
1. Plain Ice Cream 6. Parfait or New York Ice Cream
2. Nut Ice Cream 7. Puddings
3. Fruit Ice Cream 8. Custards
4. Bisque Ice Cream 9. Ices
5. Mousse 10. Sherbets
Sommer stresses that classification is based on composition rather than
ingredients used.
Plain or Philadelphia ice cream has ingredients and composition as
previously given for commercial ice cream. It may be flavored with a
variety of flavors, such as vanilla, chocolate, maple.
Nut or fruit ice creams are plain ice cream with nuts or fruit added.
Bisque is made from a plain cream basis with such additions as maca-
roons, grape nuts, dried and broken sponge cake, or marshmallows.
A mousse has a whipped cream base.
Parfait, or New York ice cream, is made from the same ingredients as
plain cream except the amount of egg used is sufficient to produce a dis-
tinctly yellow color. In some states the amount of egg yolk is specified.
Puddings differ from fruit ice cream in containing a mixture of fruits
and to justify the name pudding should have eggs in amounts similar to
New York ice cream.
Ices are made from fruit juices diluted with water and sweetened.
Sherbets are made from the same ingredients as ices with the exception
that milk, cream, or ice cream is used in place of part or all of the water
to dilute the fruit juices.
LITERATURE CITED AND REFERENCES
Ambrose, A. S. Milk Solids in Relation to the Quality of Ice Cream. Ice Cream
Trade J. 20: No. 3, 78 (1924).
Anonymous. Acidity Factor in Manufacture of Ice Cream. Ice Cream Trade J.
19: No. 8, 39 (1923).
Anonymous. How to Mix Ice and Salt Properly. Ice Cream Trade J. 9: No. 4,
42 (1913).
REFERENCES 97
Baer, A. C. Factors Influencing the Swell in Ice Cream. Ice Cream Trade J.
3: No. 3, 38 (1917).
Baer, A. C. Ice Cream Making. Wisconsin Agri. Expt. Sta. Bull. 262 (1916).
Bigelow, S. L. Theoretical Physical Chemistry. D. Appleton-Century Company,
Inc. (1921).
Brainerd, W. K. Smoothness and Keeping Qualities in Ice Cream as Affected by
Solids. Virginia Agri. Expt. Sta. Technical Bulletin 7 (1915).
Combs, W. B., and Bele, F. Cerelose in Ice Cream. Ice Cream Review 10:66,
132 (1926) ; also Ice Cream Trade J. 23: No. 1, 50 (1927).
Combs, W. B., and Martin, W. H. How Acidity Affects the Quality of Mix.
Ice Cream Trade J. 19: No. 11, 75 (1923).
Dahle, C. D. Some Ice Cream Defects and Their Remedies. Ice Cream Trade
J. 20: No. 9, 66 (1924).
Dahle, C. D. The Use and Values of Sugars in Ice Cream. Ice Cream Trade J.
20: No. 8, 46 (1924).
Dahlberg, A. C. How Ice Cream Appears Under the Microscope. Ice Cream
Trade J. 20: No. 2, 69 (1924).
Fisher, R. C. Ice Cream. Ice Cream Trade J. 20: No. 2, 69 (1924).
Fisher, R. C. Ice Cream. Ice Cream Trade J. 20: No. 3, 71 (1924).
Holdaway, C. W., and Reynolds, R. P. Melting Time of Ice Cream Determined.
Effects of Binders Upon the Melting and Hardness of Ice Cream. Ice Cream
Trade J. 13: No. 1, 25 and No. 2, 32 (1917).
Hunziker, O. F., and Nissen, B. H. Lactose Solubility and Lactose Crystal Forma-
tion. J. Dairy Sci. 9: 517 (1926).
Isenberg, G. H., and Baer, A. C. Some Commercial Ice Cream Improvers. Ice
Cream Review 10: No. 10, 104 (1926).
Leighton, A., and Peter, P. N. Factors Influencing Crystallization of Lactose.
Ice Cream Trade J. 19: No. 10, 68a (1923).
Martin, W. H. Here is How You Can Make Good Chocolate Ice Cream. Ice
Cream Trade J. 31: 19, No. 3 (1935).
Masurovsky, B. I. Newer Knowledge of Use of Gelatin in Ice Cream. Ice
Cream Trade J. 20: No. 3, 81 (1924).
Mortensen, M. Factors Which Influence the Yield and Consistency of Ice Cream.
Iowa Agri. Expt. Sta. Bull. 180 (1918).
Mortensen, M. Overrun Ice Cream Trade J. 11: No. 2, 32 (1915).
Mortensen, M. Some Factors Responsible for Desirable Texture. Ice Cream
Trade J. 20: No. 4, 74 (1924).
Ruehe, H. A. Factors which Produce Quality. Ice Cream Trade J. 20: No. 3,
74 (1924).
Sherwood, F. F., and Smallfield, H. L. Factors Influencing the Viscosity of Cream
and Ice Cream. J. Dairy Sci. 9: 68 (1926).
Sommer, H. H. The Theory and Practice of Ice Cream Making. Second Ed.
Published by the author, Madison, Wis. (1935).
Sommer, H. H., and Young, D. M. Effect of Milk Salts on the Whipping Ability
of Ice Cream Mixes. Ind. Eng. Chem. 18: 865 (1926).
Turnbow, G. D., and Milner, F. W. The Role of Gelatin in Ice Cream. J.
Dairy Sci. 10: 202 (1927).
Walker, J. Introduction to Physical Chemistry. Macmillan Co. London (1922).
Washburn, R. M. Principles and Practice of Ice Cream Making. Vermont Expt.
Sta. Bull. 155 (1910).
Williams, O. E. Benefits of Homogenization in Ice Cream Making. Ice Cream
Trade J. 20: No. 1, 63 (1924).
Williams, O. E., and Campbell, G. R. Effect of Composition on the Palatability
of Ice Cream. U. S. Dept. Agri. Dept. Bull. 1161 (1923).
98 FREEZING
FREEZING
Experiment 11.
To determine the temperature of the brine when different proportions of
ice and salt are mixed.
The ice for all the freezing experiments should be in pieces of the same size,
for the very large pieces melt more slowly because of small surface area.
Put the ice through the ice crusher, which gives pieces of more uniform size.
If it cannot be crushed in a crusher, but is broken with a hammer or shaved
with a pick, put it through a large-screen mesh to obtain pieces of uniform
size. The temperature obtained will be only approximate. For very accurate,
careful work the temperature must be taken in insulated, closed flasks.
1. Weigh Y^. pound of rock salt and an equal amount of ice. Mix well.
Find the minimum temperature that can be obtained with this mixture and
the length of time required to reach it.
Repeat using the following proportions.
2. One part of salt ( l / 4 Ib.) to 3 of ice (% lb.).
3. One part of salt (^ lb.) to 6 of ice (ft lb.).
4. One part of salt (^ lb.) to 8 of ice (1 lb.).
5. Use equal parts of sugar to ice (/^ lb. of each).
What would the result be if the above experiments were repeated using
coarse crystalline salt in place of the rock salt? Does the sugar have the same
effect as salt? Why?
Lowest temperature
obtained
Time required to reach the lowest
temperature
Conclusions and applications.
Ice Cream
Experiment 12.
To determine the effect of the rate of turning on the texture of ice cream.
Directions for freezing experiments:
The freezers for the following experiments should be in good working order.
The dashers should turn and scrape the crystals from the side of the can as
they are formed.
To find the approximate swell of the ice cream the depth of the mixture
should be measured in the can before and after freezing. If the depth is 2 inches
before freezing and 3 inches after freezing the approximate swell is 50 per cent.
The frozen mixture is not level across the top, so this method gives only an
approximate measure of the swell.
Before the freezer is packed, the dasher, lid, and handle should be put in
ICE CREAM 99
place. Otherwise in packing the can is often pushed to one side and it is difficult
to get the handle in place. See that the handle turns properly.
Measure the approximate amount of ice and salt required for your particu-
lar experiment. For a freezer of 1-quart capacity, and using the proportions 1
part of salt to 8 parts of ice by measure, about 10 cups of ice are required
for freezing. This will sometimes pack or partially pack the freezer also.
Consult the instructor for the method to use for mixing ice and salt to place
in the freezer. More uniform results are obtained with class work by mixing
the salt and ice before placing in the freezer unless uniform methods of packing
are employed. The better way of packing is to measure the ice required to
pack the freezer half way to the top. Then add a layer of salt, using Y% of
the measure of the ice. Add a layer of ice to 24 the distance from the top.
Add a layer of salt, again using % the amount of the ice. Add ice nearly to
the top of the can and the same proportions of salt. If the ice and salt are
not measured, different amounts will be used for the different groups and the
results will not be uniform, for the variables of the same experiments will
increase.
Remove the handle and lid after the ice is packed and add the mixture to be
frozen. If the freezer is the type that will freeze with the lid off, leave the
lid off and adjust the handle. By freezing in this way the ice and brine will not
come to the top of the can, but if not more than 1 cup of the mix is used in
a quart freezer the frozen mixture will not come more than half way up the
can, and the ice and salt will be sufficient for freezing.
Record the total time of turning the freezer and the time when the first
crystals are formed; notice when the swell begins. Turn until the frozen mix-
ture is the consistency of good thick gravy. Compare with your neighbors' so
that all will be of the same consistency when the freezing period is stopped.
If the freezer will not turn with the lid removed, the end point of the
freezing will need to be determined by removing the lid. Compare with your
neighbors' so that as nearly as possible all will be of the same consistency when
the creams are packed. If the lids of the freezers cannot be removed, neither
the swell nor the time when the first crystals form can be observed. Nor can
the time required for freezing be estimated very accurately. The results are
less uniform with this type of freezer and sometimes are not worth while.
Obviously, if some freezers are not in working condition the results from them
should not be recorded. If the dashers do not work properly then the results
can be used for slow-turning freezers.
Remove the dasher, put on the lid, plug the hole in the top of the lid and
pack to harden. If the period of hardening can be only a short one, a larger
proportion of salt to ice may be used for packing. Consult the instructor for
the proportions.
Freezing mixtures that contain the same proportion of ingredients will have
the same freezing point. Take the temperature while freezing in the can that is
turned slowly. Since it is to be turned slowly the results for it will not be
affected if the turning is stopped while the freezing temperature is taken.
Take the temperature of each of the frozen mixtures before tasting. During
hardening some of the frozen mixtures may reach lower temperatures than
others. Why? Because of this lower temperature they will be harder and colder.
If possible they should be the same temperature before tasting. If they are not
100
FREEZING
the same temperature in tasting do not confuse coldness and firmness of body
with texture. The body should be firm and the texture smooth and velvety,
that is, the crystals should be small and the cream should not be buttery.
An electrically operated freezer is preferable for many of the freezing
experiments, as the rate of turning can be kept uniform. But unless it has
different speeds, it cannot be used for determining the effect of rate of turning
the freezer.
It is better for two girls to work together for each of the freezing experi-
ments.
Recipe :
Cream
Sugar
Vanilla
1 cup
3 tablespoons
Y^ teaspoon
240 grams
37.5 grams
Use coffee cream containing 18 to 20 per cent fat. Dissolve the sugar in the
cream. Add vanilla and freeze.
1. Turn slowly all the time: about 40 turns or less per minute.
2. Turn slowly at first, then rapidly while freezing; 40 turns or less per
minute at first, then about 100 turns per minute.
3. Turn rapidly all the time: about 100 turns per minute.
The following headings are suggested for records of the freezing experi-
ments. After all the experiments have been performed, write a summary of
your conclusions and applications.
Freezing
temperature
Time to
freeze
Swell
Per cent
Temperature of
mix when tasted
Texture
Flavor
Results.
Experiment 13.
To determine the effect of the richness of the cream used in making ice
cream.
Use the same proportions given in Experiment 12. Use 1 part of salt to 8 of
ice. Turn slowly at first, then rapidly during the freezing period, or use an
electric freezer.
1. Use cream containing 18 per cent fat.
2. Use cream containing 24 per cent fat. If equal quantities of coffee cream
(18 to 20 per cent) and whipping cream (30 to 32) are mixed, a cream with
approximately 24 per cent of fat will be obtained.
3. Use a cream containing 30 per cent fat.
Does the amount of fat affect the freezing point? What would be the effect
of a longer freezing period on the creams with a high fat content? Would it be
advantageous to use a smaller proportion of salt for freezing these ice creams?
ICES AND SHERBETS 101
Ices and Sherbets
Experiment 14.
To determine the best proportions of ice and salt to use in freezing an ice.
Recipe :
Water 1 cup 240 grams
Sugar yz cup 100 grams
Lemon juice ^4 cup 60 grams
Dissolve the sugar in the water and bring to the boiling point. Cool to 30C.
and add the lemon juice, then freeze. Turn the freezer slowly at first, then
rapidly or use an electric freezer. Try each of the following proportions of salt
and ice. See freezing directions, Experiment 12. Compare the consistency of
the frozen ices, the fineness of the crystals, and the flavor. Compare the swell
obtained with the different proportions of ice and salt.
1. Use 1 part of salt to 3 of ice.
2. Use 1 part of salt to 6 of ice.
3. Use 1 part of salt to 8 of ice.
4. Use 1 part of salt to 12 of ice.
What is the proportion of ice and salt given in cook books as best for freez-
ing ices? Are your results in accordance with these proportions? Are the best
proportions for an ice and for an ice cream the same?
What would be the effect of adding a larger proportion of sugar to the
recipe? If you wish to add whole strawberries or other fruit to a frozen
dessert, how would you treat them to prevent their freezing into chunks of
ice?
Experiment 15.
To determine the effect of the rate of turning the freezer upon the texture
of an ice.
Use the proportions of salt found best in Expe-riment 14. See Experiment 12
for freezing directions.
Notice when the ice begins to turn white. When does the swell begin?
Compare the texture of the finished products.
1. Turn slowly all the time, about 40 turns or less per minute.
2. Turn slowly at first, 40 turns or less per minute; then rapidly while
freezing, about 100 turns per minute.
3. Turn rapidly all the time, about 100 turns per minute.
4. If you have a vacuum freezer use it for one lot, or freeze one lot in the
mechanical refrigerator.
Experiment 16.
To determine the effect on the texture of an ice when a binder is added.
Use 1 part of salt to 8 parts of ice or the best proportions found in Experi-
ment 14. See Experiment 12 for freezing directions.
1. Prepare the lemon ice as given in the recipe for a control.
2. To the recipe given add ^ teaspoon of gelatin. Hydrate the gelatin
102 FREEZING
by letting it stand a short time with 1 tablespoon of water. Then dissolve in
the hot sirup.
3. To the half-frozen ice, add ^ egg white beaten stiff. Finish freezing.
4. Prepare lemon ice adding both ^2 teaspoon of gelatin and l /2 egg white
beaten stiff. See 2 and 3 for directions for adding to the ice.
5. Pour the hot sirup over ^2 egg white beaten stiff. Beat while adding the
sirup. Cool, add lemon juice, and freeze.
6. Repeat 1, but do not make a sirup of the sugar and water. Dissolve the
sugar in the cold water, add the lemon juice, and freeze.
7. Repeat 6, but substitute milk for the \vater.
Which mixtures give the best textures? Which are the easiest to prepare and
freeze ?
Results.
Suggestions for Additional Experiments
To determine the effect on the texture of ice cream when a filler is used.
Recipe:
Cream /^ cup 160 grams
Sugar 3 tablespoons 37.5 grams
Milk Y^ cup 80 grams
Vanilla l /^ teaspoon
a. Add Y\ tablespoon of flour (5.3 grams) to the recipe. Boil and cool before
freezing.
b. Add }/4 beaten egg (12 grams) to the recipe. Scald. Cool, then freeze.
To find the effect of aging the cream. Use cream with the same percentage
of fat, but have one lot 24 hours older than the other.
To find the effect of homogenizing the cream. Use cream of the same per-
centage of fat and the same age but have one lot homogenized, the other
unhomogenized.
CHAPTER IV
FRUITS AND VEGETABLES
Losses in Cooking Vegetables
The losses that occur in cooking fruits and vegetables are of three types :
first, the losses due to volatile substances ; second, the losses due to the solu-
bility of some of the substances of the fruit or the vegetable in water during
preparation and cooking, and the discarding of this water; third, the losses
due to the destruction of some substances by heating.
The volatile loss is composed largely of water but includes some acids
and substances that give flavor and odor. The greatest part of the volatile
loss can be replaced by the addition of water. The other volatile substances
affect the flavor more than the food value and will be considered later.
Water in which fruit is soaked and cooked is seldom discarded, so that
this type of loss pertains more to the cooking of vegetables. Vegetables
contain the following food nutrients: protein, fat, carbohydrates, minerals,
and vitamins. Decrease of these nutrients during cooking is due largely to
their loss. Vegetables contain little fat, thus fat loss in their cookery is
relatively unimportant. The starch from vegetables is insoluble in water.
The loss of starch from vegetables occurs when the cell walls are broken
by cutting in preparation, disintegration through over-cooking or from
abrasion, which may occur in violent boiling and cause the sloughing off of
parts of the vegetable near the surface.
Nitrogen. The nitrogenous or nitrogen-containing part of fruits and
vegetables may be classified for convenience as composed of proteins and
non-proteins. The nitrogenous content of vegetables, with the exception of
the legumes, is low. The albumins are soluble in water and dilute salt
solutions, the globulins in dilute neutral salt solutions. They are both
coagulable by heat. Their greatest loss would occur when the vegetable is
soaked before cooking, or when cold water is added to the vegetable to
start the cooking process. In salted water some of the albumins and globu-
lins would be dissolved.
McKee and Smith in their investigations of the protein of the cauli-
flower found that 68 per cent of the nitrogen of the edible part belongs
to constituents soluble in water or dilute salt solution; 12 per cent to
compounds soluble in 0.3 per cent sodium hydroxide, but not soluble in
water; and 16 per cent to substances insoluble in either water or dilute
alkali. Their results show a large proportion of the nitrogen compounds
103
104 FRUITS AND VEGETABLES
soluble in water and dilute salt solution, indicating that it is preferable
to start cooking in boiling water to coagulate the albumins and globulins.
Some of the nitrogenous substances are soluble at all temperatures. The
foaming of the cooking water is partially due to these substances, and par-
tially to tannins and saponins. All these substances lower the surface tension
of the cooking water and favor foaming. Foaming occurs in the cooking
of some vegetables, such as peas and asparagus, more than in others.
The important changes in the cookery of vegetables come from the loss
of sugars, vitamins, and minerals. The sugars are very soluble in cold and
hot water. Their loss is lessened if the vegetable is left in large pieces,
which give less surface for contact with the water than small pieces.
Vitamins. The loss of vitamins in cooking may come from destruction
by heat or by oxidation as well as loss in the discarded cooking water.
Mineral salts. The principal minerals in foods that may be lost
during cooking are the salts of sodium (Na), potassium (K), calcium
(Ca), magnesium (Mg), phosphorus (P), sulfur (S), iron (Fe), chlorine
(Cl), and iodine (I). Sodium, potassium, magnesium, and calcium are a
valuable part of the mineral content of fruits and vegetables, as an excess
of this group over the phosphorus, sulfur, and chlorine group produces an
alkaline ash reaction in the body after the food nutrients have been ab-
sorbed from the intestinal tract. Potassium particularly is found in high
percentage in most vegetables. Most of its salts as well as those of sodium
are quite soluble in water so that their loss in discarded cooking liquor
may be high. As a rule, the calcium salts are not so soluble as the other
salts found in vegetables; in some vegetables they seem to be in an in-
soluble form, but in others the calcium loss is about one-fourth of the
total calcium of the food. Magnesium salts are more soluble than those of
calcium. Vegetables, with the exception of the legumes, contain small per-
centages of phosphorus when compared with some other foods. The phos-
phorus salts are easily soluble, and the phosphorus loss in discarded water
may amount to 50 per cent or more of the total phosphorus of the vege-
table.
The solubility of most of the salts found in vegetables increases with
increasing temperature of the water, so that at 100C. they are more
soluble than at ordinary temperatures.
Peterson and Hoppert, using medium and large quantities of water for
cooking vegetables, report the loss of calcium to be practically nothing in
spinach. In other vegetables the loss is about 30 per cent of the total cal-
cium. They report that the magnesium loss varies from 20 to 45 per cent,
the phosphorus from 20 to 50 per cent. Berry reports as high as 60 per cent
for magnesium and 52 per cent for phosphorus.
The following losses for cooking vegetables in water are reported in
U. of Minn., Agri. Expt. Sta. Bull. 54, and in U. S. Dept. Agri. Farmers'
Bull. 73.
IRON
105
TABLE 13
LOSSES IN COOKING VEGETABLES VARIOUS WAYS IN WATER
Loss of total
Loss of total
Loss of total
Vegetable and method
nitrogenous
matter,
mineral,
sugar,
per cent
per cent
per cent
Potatoes peeled and soaked
several hours before cook-
ing
52
38
"*&
Potatoes started to cook in
cold water
16
19
Potatoes, cooking started in
boiling water
8
about 19
Potatoes cooked in skin
trifling
trifling
Carrots cut in small pieces. . .
42
47
26
Carrots cut in medium pieces
less than
less than
26
42
47
Carrots cut in large pieces . . .
20
25 plus
16
Cabbage, started in hot water
about 33
about 33
. .
Cabbage, started in cold water
about 50
about 50
Iron. The iron of foods is very important nutritionally, because of
the fact that many dietaries do not contain the minimum daily amount
recommended by Sherman. The loss of iron in cooking should be avoided.
Iron salts are quite soluble. Blunt and Otis report the following losses of
iron when the vegetables were cooked in water: spinach 43 per cent;
string beans 39 per cent; navy beans 32 per cent; peas 36 per cent; and
TABLE 14
IRON Loss IN SALTED AND UNSALTED WATER (Steinbarger)
Vegetable
Unsalted water,
per cent
Salted water,
per cent
Potatoes cut in halves
63.2
83.7
Carrots
16.4
27.8
Cabbaee
27.4
40.7
Onions ...
46.5
71 4
Cauliflower
30 7
47 4
Spinach
19 3
46 8
Green beans
24 5
38 8
106 FRUITS AND VEGETABLES
potatoes 15 per cent. Peterson and Hoppert report from 20 to 30 per
cent iron loss for various vegetables. Morgan reports 46 to 50 per cent
loss for canned peas.
Steinbarger reports the loss of iron as greater in salted than in unsalted
water. Table 14 is from her results.
The vegetables given in Table 14 were cooked the following lengths
of time: potatoes and onions 20 minutes; green beans 90 minutes; and the
others 30 minutes. The results suggest some connection between iron salts
and the globulins. The iron salts of potatoes have been reported as more
concentrated near the surface, which may account for their high iron loss.
Losses due to method of cooking and preparation. The losses
through cooking of vegetables depend upon several factors, which include :
(1) the method of cooking, (2) the nature of the vegetable, (3) its prep-
aration, (4) the length of time of cooking, (5) the temperature of cooking,
(6) the quantity of cooking water, (7) whether started in hot or cold
water, and (8) the reaction of the cooking medium. Some of these have
been considered under nitrogen and vitamin losses.
Baking results in small nutritive losses.
All investigators report small losses in steaming; this seems to be an
ideal way of cooking vegetables whose color and flavor are not altered
by this method.
Masters and Garbutt report practically no loss in cooking vegetables in
water, if the amount of water added is small and is evaporated just to
dryness at the close of the cooking period. They designate this as the
conservative method of cooking. If it is not practicable to evaporate the
water to dryness, the use of as small a quantity of water as possible seems
preferable to using a very large quantity.
Leafy vegetables like spinach offer a larger surface area for loss than
the compact ones like carrots. Soaking in water before cooking may increase
the losses, and vegetables like carrots and potatoes, when cooked whole,
in their skins, or left in large pieces lose less than if cut in small pieces.
Loughlin reports that the amount of the sugars, the vitamins, and mineral
salts dissolved in the cooking water is increased if a large amount of liquid
is used, if much cut surface is exposed, and if the cooking time is prolonged.
Thompson reports that the total loss of solids, ash, and iron is greater
in vegetables that are over-cooked than in those just sufficiently cooked.
The Plant Acids
The plant acids, the plant pigments, and the cellulose are constituents
of the vegetable less often considered than the other food nutrients. Knowl-
edge of the common reactions of these constituents renders one able to
serve fruits and vegetables that are attractive in appearance, color, and
texture.
ACIDS IN VEGETABLES 107
Plant acids. Plants contain organic acids. According to chemical
classification the acids may belong to different groups, but for consideration
in cooking they may be divided into two classes, the volatile and non-
volatile ones. Volatile acids are the ones that volatilize and pass from the
liquid as vapor. The odor of acetic acid or vinegar during cooking is well
known. The following acids .of the C n H 2n O2 series are volatile, the first
ones being more volatile than the last ones:
Formic acid H COOH
Acetic acid CH 3 -COOH
Propionic acid CH 3 CH 2 COOH
Butyric acid CH 3 -CH 2 -CH 2 -COOH
Valeric acid CH 3 CH 2 CH 2 - CH 2 COOH
Caproic acid CH 3 - CH 2 CH 2 CH 2 - CH 2 - COOH
Formic and acetic acids have been obtained from plants during distilla-
tion. Onslow states that propionic acid has only rarely been found in
plants.
The amount of volatile acids found in plants varies ; it also varies in the
same plant. Koch found that cooking 125 grams of spinach for 1 hour and
collecting the distillate required 18 cc. of AT/10 NaOH to neutralize the
volatile acids. Another experiment in which the same weight of spinach was
used and cooked for the same length of time required only 6 cc. of N/IQ
NaOH.
Non-volatile acids. Not all the acids found in fruits and vegetables
are volatile. The following are some of the more common non-volatile ones
found in foods :
Dicarboxylic acids
Oxalic acid COOH- COOH
Malonic acid COOH CH 2 COOH
Succinic acid COOH - CH 2 CH 2 COOH
Glutaric acid COOH (CH 2 ) 3 - COOH
Adipic acid COOH (CH 2 ) 4 COOH
Hydroxydicarboxylic acids
M alic acid COOH CHOH - CH 2 COOH
Tartaric acid COOH CHOH - CHOH - COOH
Hydroxytricarboxylic acids
Citric acid " COOH .CH 2 .COH-CH 2 . COOH
I
COOH
Acids in vegetables. The acids are found in the fruits, leaves, stem,
and root stocks. The acid may occur in the free form, but is often com-
bined as a salt or an ester.
Because of oxaluria the oxalic acid content of vegetables is of interest.
Onslow states that oxalic acid "occurs very frequently and widely dis-
108 FRUITS AND VEGETABLES
tributed in plants, usually as the calcium salt, and apparently less fre-
quently as the sodium and potassium salts. It has rarely been detected as
the free acid. The calcium salt is precipitated on adding calcium acetate
to a solution of the acid. Calcium oxalate is insoluble in acetic acid, but
soluble in dilute mineral acids." It is found in the rumex or dock family,
of which different docks and sour grass are used as food. Sorrel and rhubarb
contain a rather high percentage. Rider has reported the most extensive
determinations of oxalic acid in leafy vegetables. She has found that the
amount in spinach ranges from 0.486 to 0.692 per cent. Beet greens give
an equivalent or slightly higher amount than spinach, and New Zealand
spinach contains a still higher percentage. No oxalic acid was found in
dandelion greens, kale, turnip greens, and mustard greens. McLaughlin
has reported the oxalic acid content of eight samples of New Zealand
spinach as ranging from 0.49 to 0.53 per cent, anhydrous. As these figures
indicate, the amount in different samples of the same vegetable may vary.
Rider mentions this fact in connection with the samples she analyzed.
Nelson has reported 0.31 per cent oxalic acid in spinach.
Succinic acid is found in many plants, and glutaric and adipic have been
isolated from the sugar beet.
Malic acid is found as the free acid and as the salts of malic acid in
many plants, and particularly in apples and pears.
Citric acid is found in tomatoes and it is found in smaller quantities in
other foods. Blunt reports small amounts in cabbage, asparagus, and string
beans.
Nelson has reported that spinach contains both citric and malic acids. The
ratio of citric to malic acid in broccoli was 3 :2. The leaves and buds
contained approximately the same proportions. Small amounts of oxalic
and succinic are also present. The acid content of lettuce was as follows:
oxalic, 1 -malic, and citric, 0.011, 0.065, and 0.048 per cent respectively.
Tomatoes, which have the highest amount of acid of our common
vegetables, contain citric acid. Blunt reports 0.42 per cent.
The acids found in fruits. Conflicting reports appear in the literature
regarding the particular acid in different foods. Bigelow and Dunbar sug-
gest that this is due to the inaccurate methods of analysis often used and
to the difficulty in separating the different acids from one another. Nelson
has reported the approximate percentages of the various acids in fresh
fruits, the average total acidity being calculated as citric. His results are
given in Table 15.
Nelson states that the most common acids in fruits, citric and malic,
may occur in different proportions or one alone may be present. "The
total acidity of most fruits varies with the variety and the degree of ripe-
ness. The relative proportions of the various acids may also vary with the
degree of ripeness, variety, and climatic and soil conditions."
Rhubarb contains some oxalic acid ; cranberries and plums some benzoic.
Other acids sometimes found in small quantities are succinic, lactic, iso-
ACIDS FOUND IN FRUITS
109
TABLE 15
THE ACIDS OF FRUITS (Nelson)
Fruit
In-
ves-
tiga-
tor
Cit-
ric
%
Mal-
ic
%
Tar-
tar-
1C
%
Ben-
zoic
07
70
Oxal-
ic
%
Suc-
cin-
ic
%
Lac-
tic
Of
%
Iso-
cit-
ric
%
Total
acidity
(titrat-
able) %
Apple (\Vinesap)
N
trace
50
51
Apricot (dried)
N
35
81
trace
1.16
Banana
p
24
26
Blackberry
Blueberry
N
N
trace
1 56
0.16
10
trace
trace
0.92
1.08
1 66
Cherry
F
01
1 25
trace
07
0.13
1.36
Cranberry
N
1 82
46
07
2 35
Currant
F
2.30
0.05
trace
trace
2.35
Fig
N
34
trace
0.35
Grape
N
65
43
1.08
Grapefruit
H
1 46
1.46
Lemon
N
3 84
trace
3 88
Loganberry
N
2 02
08
2.10
Orange
N
98
trace
99
Peach
N
37
37
0.74
Pear
N
24
12
0.36
Pineapple
N
84
12
0.96
Pomegranate
N
1 25
1.25
Quince
N
68
68
Raspberry, blk
N
1 06
1.06
Raspberry, red
N
1 30
04
1.34
Rhubarb
N
41
1 77
12
2.30
Strawberry
N
91
10
1.01
Tamarind
F
trace
50
7 76
trace
trace
8.00
Tomato
N
30
20
0.50
F refers to Fransen: N to Nelson: H to Hartman: and P to Pratt.
citric, and acetic. Nelson reports acetic acid in figs, isocitric in blackberries,
and tartaric in grapes. Bigelow and Dunbar have reported that both citric
and malic acids are found in gooseberry, the total acid for different varieties
varying from 1.72 to 2.63 per cent.
Mineral salts of organic acids may be formed during the cooking of
fruits in metal containers. Very unpalatable flavors are developed in this
way, and the color of the cooked product is darkened. This brings to
memory a sample of plum butter sent to the Department. It was nearly
charcoal black in color, and as for flavor might have been made from
any fruit, for there was little of the original fruit flavor left. The sender
stated it had been cooked on the back of the stove in a tin wash boiler
for three days and was much perturbed because a neighbor had told her it
was poisonous on account of the cooking utensil used. Hence a sample was
sent with the request to try it and see if it was poisonous.
110
FRUITS AND VEGETABLES
Just as inorganic acids may combine with metals to produce acid or
neutral salts according to whether part or all of the hydrogen is replaced
by the metal, so in a similar way organic acids may combine with metals
forming salts.
Thus oxalic acid gives
COOH
COOH
oxalic acid
KOH
potassium
hydroxide
H 2
COOK
COOH
water acid potassium
oxalate
COOH
+ 2 KOH
COOH
oxalic acid potassium
hydroxide
2H 2 +
COOK
COOK
water potassium
oxalate
Zinc utensils. Some of the metal salts formed with organic acids are
injurious when taken into the body. The zinc salts of organic acids have
been regarded as toxic. They are formed when foods containing acids are
placed in galvanized containers. Galvanized iron contains some zinc, and
when fruits, beverages, or even milk are placed in utensils made of it, the
acids of the food combine with the zinc, forming salts.
Sale and Badger have reported that zinc is dissolved from galvanized
utensils, and the greater the acidity of the food and the longer the food
stays in such containers the more zinc dissolved. Even fresh milk contains
enough acid to dissolve appreciable amounts of zinc.
Burke, Woodson, and Heller, after investigating the toxicity of butter-
milk held in galvanized containers, question the attributing of the toxicity
to zinc in many previous investigations, and think that in some cases the
toxicity may have been due to the surface of the galvanized container being
contaminated with some other substance, possibly arsenic, lead, or antimony.
The tin salts have not been found poisonous, but large amounts of them
in a food, such as would result when an acid fruit is cooked for a long
time in a tin wash boiler, produce a very dark color and a disagreeable
metallic flavor.
Iron salts with acids may cause discoloration in some food products.
Plant Pigments
Chlorophyll. Chlorophyll, the green pigment of plants, plays an im-
portant role in their synthesis of carbohydrates. The cells of the mesophyll
of the leaf contain chloroplasts or chlorophyll-corpuscles, the nucleus, other
substances, and the cell liquid with its dissolved materials. The chloro-
plasts contain four pigments, two green ones, chlorophyll a and chlorophyll
b, and two yellow ones, carotene and xanthophyll.
Solubility of chlorophyll. Chlorophyll is not soluble in water. Very little
CHLOROPHYLL 111
green color is found in the water in which green vegetables have been
cooked. Pure isolated chlorophyll is soluble in acetone, ether and benzene.
In extracting the pigment from thoroughly dry leaves it is necessary to add
about 20 per cent of water to the acetone or other solvent. One explana-
tion for this is that chlorophyll is in the colloidal state in the leaf, and
the mineral constituents of the leaf, dissolved in the water, peptize it,
rendering it soluble. Onslow states that "the condition of chlorophyll is
altered by plunging into boiling water. The pigment is then much more
soluble, in ether, etc., even when the leaves are subsequently dried. It is
supposed that the chlorophyll has diffused out from the plastids, and is in
true solution in the accompanying waxy substances which have become
liquid owing to change in temperature."
When green vegetables are dropped into boiling water a change takes
place nearly instantly, the green color being intensified. Various explana-
tions have been offered for the phenomenon. One is that the hot water has
melted waxy constituents of the leaf so the chlorophyll escapes from the
cell more readily or may become more soluble. Or the hot water may have
dissolved salts or other substances in contact with the chlorophyll so that
it diffuses more readily.
For peas, Kohman states that one factor in the intensification of the
green color is the removal of air from the pea when it is dropped in the
boiling water. The outer skin of the pea is transparent, the space beneath
this being impregnated with air which is removed when the peas are
blanched. That this change in color is caused by removal of the air can be
shown by subjecting the peas to an adequate vacuum under cold water
and releasing the vacuum while the peas are still under the water.
Composition of chlorophyll. Willstatter, whose work gave us the formula
for and the chemical reactions of chlorophyll, reports that it exists in two
forms, depending upon the degree of oxidation in the plant cells: form (a)
and form (b). The former exists in the proportion of three to one of the
latter.
COOCH 3 COOH
COOC 20 H 39 COOH
chlorophyll a chlorophyllin
COOCH
C 32 H 28 2 N 4 Mg/
chlorophyll b
Chlorophyll contains 2.7 per cent of the metal magnesium. It contains
two ester groups, one of methyl alcohol (COOCH 3 ) and one of phytol
alcohol (COOC 20 H 3 9).
112 FRUITS AND VEGETABLES
Reactions of chlorophyll with alkalies. Chlorophyll is a neutral substance
but gives characteristic reactions when treated with alkalies or acids. Will-
statter designates the parent substance of chlorophyll as chlorophyllin. The
reaction of chlorophyllin with methyl and phytol alcohols gives the ester
chlorophyll. Chlorophyll, when treated in the cold with alkalies, gives
alkaline salts of chlorophyllin. The color change is first brown, followed
by a return of the green, but it is no longer fluorescent. When chlorophyll
is saponified with hot alcoholic alkalies, isochlorophyllins are formed, which
are fluorescent.
COOCH 3
C 32 H 30 ON 4 Mg/ + 2 MOH
COOC 20 H 39
chlorophyll a alkali
COOM
C 32 H 30 ON 4 Mg/ + CH 3 OH + C 20 H 39 OH
COOM
alkali salt of chlorophyllin methyl phytol
alcohol alcohol
When the green-colored vegetables are cooked in water with an alkaline
reaction, or in water to which a small amount of soda is added, they
develop a bright, intense green color.
Reaction of chlorophyll with acids. Chlorophyll reacts with acids to
give an olive-colored product, without fluorescence, called phaeophytin. The
magnesium of the chlorophyll is replaced by hydrogen. From phaeophytin,
Willstatter has obtained two decomposition groups: the first, designated as
phytochlorins, are olive green and derived from chlorophyll a] the second,
the phytorhodins, are red and derived from chlorophyll b.
COOCH 3
C 32 H 30 ON 4 Mg/ + 2Hx
C_>OOC-/2oJ~l3g
chlorophyll a acid
(C 32 H 32 ON 4 ) (COOCH 3 ) (COOC 20 H, 9 ) + Mgx 2
phaeophytin magnesium
salt
The effect of heat upon chlorophyll. The chlorophyll is changed to the
olive-green color by two means, ( 1 ) by hydrogen ions or an acid reaction and
(2) by heat. As previously given, the hydroxyl ions, or an alkaline reac-
tion, produces chlorophyll salts with bright green color. In general, the
more acid the reaction, the more rapid is this change in color w r hen the
vegetable is heated ; or, vice versa, the more alkaline the reaction, the more
slowly the chlorophyll changes to olive-green. Thus in order that the bright
green color be retained in cooking green vegetables, they should be cooked
CHLOROPHYLL 113
for as short a time as possible and contact with acids should be avoided as
far as possible. It is also possible that other ions than the hydrogen and
hydroxyl ions may affect the stability of the chlorophyll, for some vege-
tables with nearly the same />H, cooked in water from the same source,
and with other conditions standardized are more stable to heat than others.
In cooking certain procedures may aid in decreasing the acidity of the
cooking water. The vegetables contain both volatile and non-volatile acids,
which in the plant are prevented from uniting with the chlorophyll but
are liberated when the plant tissues are heated. If the cooking vessel is not
covered, the volatile acids may escape with the steam, thus decreasing the
acidity.
It has been found that the highest percentage of these volatile acids
passes off during the first few minutes of cooking. Hence, if the cooking
vessel needs to be covered for a part of the time, it is preferable to have
the uncovered period the first few minutes.
Certain water, such as hard water, softened water, or water from many
streams, is alkaline in reaction. Rain water, snow, or ice water is usually
about neutral. If the cooking water contains alkaline salts, these salts may
neutralize the non-volatile acids, and if there is a slight excess of alkaline
salts the green color is intensified. To a certain extent the intensification
depends upon the quantity of water used, for the larger quantity of water
contains a greater quantity of alkaline salts. If the water is only slightly
alkaline the plant acids may not all be neutralized and the olive-green color
may develop. If the water is very alkaline and considerable water is used,
not enough volatile and non-volatile acids will be liberated to neutralize
the alkalinity of the water, the cover can be kept on during cooking, and
the product will be bright green. With longer cooking the heat may have
more effect upon the chlorophyll than the alkaline salts of the water. The
addition of sodium bicarbonate (baking soda), Experiment 17A, 5, also
intensifies the green color. Canned spinach, asparagus, peas, and string
beans have a deep olive-green color due to the retention of the plant acids
during processing and to the high temperature at which they are processed.
Green vegetables like cabbage, Brussels sprouts, and spinach cooked in
milk may remain a bright green color. Owing to the ease with which milk
scorches and boils over there is usually less tendency to cook the vege-
tables too long when milk is used.
Heat decomposes chlorophyll, an olive-green color being produced. The
extent of decomposition depends upon the time of heating and the tem-
perature reached. With a very short cooking period little destruction may
occur, but with a longer time all the chlorophyll may be decomposed. At
lower temperatures the change is less rapid and at higher temperatures
more rapid. Thus in a pressure cooker the change is rapid, since the tempera-
ture is high and acidity is not decreased because the volatile acids are
retained. Increasing the alkalinity by using alkaline water or adding soda
114 FRUITS AND VEGETABLES
retards the color change by heat. However, the addition of soda is not
advisable, because it softens the cellulose rapidly so that the vegetable with
slight over-cooking becomes mushy or even slimy and the destruction of
some of the vitamins is hastened.
The cooking of green vegetables that contain enough acid to taste sour,
like sorrel, sour grass, and dock, always produces this olive-green color
no matter how cooked or for how short a time. Their acid content is too
high to be neutralized by the alkaline salts of water or the addition of
baking soda in small amounts. Green fruits like gooseberries, green grapes,
and green plums develop an olive-green color when cooked. If the fruits are
mature they may also contain yellow pigments that modify the color to a
certain extent.
If acid is to be added as a seasoning to green vegetables it is preferable
to add it when served, for there will not be so long a time for the acid
to react on the chlorophyll and less brown color will develop. When
vegetables are cooked with added acid, the softening of the vegetable is
prevented to a slight extent.
Replacing magnesium in chlorophyll products. It is very difficult to re-
place the magnesium of the magnesium-free chlorophyll products. It can
be done chemically by using a very reactive substance, magnesium methyl
iodide, but this is impracticable to use in cooking processes. However, Will-
statter states that the acetate salts of some metals such as copper, iron, and
zinc will combine with phaeophytin and give very bright green-colored
products. This is such a good test for small quantities of these metals that
it is necessary in isolating chlorophyll to be extremely careful that it does
not come in contact with them. If to the green vegetable to which acid has
been added and in which the olive-green color has developed, Experiment
17A, 6, copper acetate is added, a vivid green color will develop on
standing.
Carotinoids. Carotinoids is a term applied to the pigments giving yel-
low and orange coloring to fruits and flowers, carotene, C^H-.o, and
xanthophyll, C^HseOo. The Carotinoids are not soluble in water, and the
pigments are not affected, to any great extent, by the concentration of
acids or alkalies used in food preparation. The darkening produced by the
action of alkalies by caramelization of the sugar in vegetables, like carrots,
must not be confused with a change in pigment color. Carotene is easily
oxidized when exposed to air. Xanthophyll can also be oxidized in the same
way. One of the characteristics of the Carotinoids is the intensity of their
coloring. The red pigment found in tomatoes is lycopin, an isomer of
carotene.
Flavones and Flavonols. Flavones and flavonols are amphoteric pig-
ments found in vegetables and petals of flowers. They are also found in the
cell sap of the epidermis and underlying tissue of plants. Onslow gives the
following formulas :
FLAVONES AND FLAVONOLS
115
/\
As they occur in nature they often have other or additional hydrogen
atoms replaced by hydroxyl groups. The position of the hydroxyl groups
markedly influences the intensity of color, the color usually being deeper
if two hydroxyl groups are in the ortho position to each other. The flavone
and flavonol pigments are yellow in color. In plants they often occur as
glucosides, one or more of the hydroxyl groups being combined with the
sugar, and then the color is less intense. They give an intense yellow color
with alkalies. Sometimes the quantity of them found in white vegetables
is so minute that they are not visible. Adding an alkali or holding them
over ammonia vapor intensifies the color and they become visible. The
color changes of the flavones cannot be observed so readily in the yellow,
red, or green vegetables.
Rice cooked in alkaline water usually has a yellow tinge, and sometimes
it is rather deep in hue or has a green tint. Rice from the same source as
that cooked in alkaline water, but cooked in distilled water, has a snowy
white appearance.
The cooking of cauliflower, white cabbage, and particularly white onions
in alkaline water often causes the yellow color to develop. Some white
onions cooked in the hard water at Ames have developed nearly a sulfur
yellow in color, whereas portions of the same onions cooked in distilled
water remained white, or retained their natural yellow tinge.
Potatoes must often contain flavones, as they sometimes develop a yellow
or green color in alkaline water. Mashed potatoes that have a strong
alkaline taste may be improved in flavor by adding a very small amount of
cream of tartar.
Flavones and flavonols with iron salts turn green and then brown. This
116 FRUITS AND VEGETABLES
may explain some color changes that occur when foods are cooked in
chipped enamel utensils having an iron base.
Anthocyanins. The anthocyans include a group of pigments that, like
sugars, have similar composition and properties yet have individual dif-
ferences. As a rule they occur as glucosides in different parts of the plant
and are known as anthocyanins in this combination. When the glucoside is
hydrolyzed by boiling with dilute acid the non-glucosidal pigment portion
is called anthocyanidin. The anthocyanins are soluble in water. Onslow
states that occasionally they crystallize from the cell sap. Most but not all
of the anthocyanins are soluble in alcohol. The anthocyan pigments give
the blue, purple, violet, and red shades to different parts of the plant.
They are very widely distributed. Onslow states that the plant that does
.not produce them is the exception rather than the rule. They occur in
apples, cherries, currants, grapes, blueberries, red and black raspberries,
in some varieties of peaches and plums, and in red cabbage, radishes, beets,
and other fruits and vegetables.
All the anthocyanins so far isolated have fallen into one of three groups.
They are illustrated as the chlorides. The number of hydroxy groups
attached to the side benzene ring is made the basis of the classification.
The glucosides of these anthocyanidins are called pelargonins, cyanins, and
delphinins.
One of the reactions that the anthocyanins have in common is their
color changes. Onslow states that the pigment should be pure to test the
color reactions, for in the plant the pigment is found with other substances
that may modify the reaction. In an acid solution, pure anthocyans are
usually red ; in an alkaline one they are violet or blue, but if flavones or
flavonols are present, a green color is obtained through the mixture of the
blue and yellow. Yet the solutions of many fruit juices show typical color
changes. In ordinary solutions of plant pigments they become green, then
yellow, and sometimes brown upon the addition of alkali. If the alkali is
very weak, or with salts with a weak alkaline reaction, a blue color may
form and the green may never develop, or the blue may be intermediate
between the red and the green.
Color changes of fruit juices. Pratt and Swartout state that the solu-
tions of many fruit pigments act as indicators ; that the solutions are easily
prepared and stable; that the liquid indicators can be used in titrating
acids, but not bases, for in a solution no more than moderately alkaline
they soon decompose, all of them producing a brown color which does not
change when acid is added. They found that apricots, peaches, pears, per-
simmons, and tomatoes failed to yield pigments that could be used as in-
dicators. It is interesting that the pigment of cactus holds its red color
even in a distinctly alkaline medium. They also state that "the pigment of
red beets remained red through the acid range and into the alkaline range
at least as far as />H 13.0." In their conclusion they recommend that the
greatest usefulness of the indicators is in test papers.
ANTHOCYANINS
117
OH
pelargonidin chloride
/ \ y
HO^
OH
\ /
\
v/ \
OH H
cyaninidin chloride
C-OH
OH H
delphinidin chloride
colors and punch. Combinations of fruit juices for punch can yield
beautiful, clear colors, or ugly, muddy ones. If a red color is desired, use
red- or blue-colored juices and keep the reaction acid by the addition of
lemon juice. For a purple shade, choose fruit juices nearly neutral in
reaction and do not add lemon juice. A blue color can usually be intensified
by the addition of canned pineapple juice. (See the following paragraph.)
Alkaline water may or may not give a bluish tinge to red fruit juices,
depending on the alkalinity of the water and the acidity of the juice. Orange
118
FRUITS AND VEGETABLES
TABLE 16
THE pH RANGE WITH COLOR CHANGES OF FRUIT JUICES (Pratt and Swartout)
Fruit source
Color change
pH range
Apples
Red to yellowish-green
6.2- 7.2
Blackberries
Red to dark grayish-blue
6.0- 7.4
Blueberries
Reddish-purple to greenish-purple
6.2- 7.2
Cactus
Red to faint purple
9.0-12.0
Cactus
Faint purple to reddish-brown
12.0-13.0
Cherries
Red to bluish-purple
6.0- 7.2
Grapes
Red to purple
5.0- 6.6
Grapes
Purple to green
6.6- 7.6
Plums
Red to yellowish-green
6.2- 7.2
Pomegranates
Red to purple
6.0- 6.8
Pomegranates
Purple to green
6.8- 7.6
Strawberries
Red to yellowish-green
6.2- 7.2
TABLE 17
THE COLOR OF FRUIT JUICES IN NEUTRAL, ACID, AND ALKALINE MEDIUMS
(Pratt and Swartout}
Fruit source
Neutral tint
Acid tint
Alkaline tint
Apples
Grayish-purple
Red
Green
Blackberries
Purple
Red
Bluish-green
Blueberries
Purple
Red
Blue
Cherries
Reddish-purple
Red
Bluish-green
Cranberries
Faint purple
Red
Light green
Grapes
Purple
Red
Bluish-green
Plums
Faint purple
Red
Light green
Pomegranates
Purple
Red
Bluish-green
Strawberries
Reddish-purple
Red
Light green
juice should be added to red or blue fruit juices only when a brownish
or magenta shade is desired, for often this combination is not attractive.
From the colors produced, or unless very small proportions of one color
are used, the red and yellow, blue and yellow, or green and yellow com-
binations should be avoided.
The color change obtained by the addition of canned pineapple juice
to grape, wild grape, blackberry, raspberry, or loganberry juices cannot be
explained on the basis of acidity alone. Even if these juices have had a
large quantity of lemon juice added they usually turn blue or the original
ANTHOCYANINS 119
blue shade is intensified and particularly after the juices have been mixed
and left standing a short time. Tin salts from the canned pineapple may
be one cause for the color change. In addition, proteins, tannins, and ferric
salts may play a role in causing color changes. Also many of the salts of
the anthocyanins have characteristic colors which are independent of mild
changes in acidity. Many organic substances also have characteristic color
changes.
Violet colorations in canned fruits. Culpepper and Caldwell have re-
ported the cause of violet coloration of some fruits canned in tin con-
tainers. The red anthocyan pigments have the property of combining with
tin, forming salts that are violet colored. The salts are formed when the
material containing the pigment is heated with tin. They find that "the
amount of the violet compound formed is determined by the amount of
pigment present, and by the degree of acidity of the medium, low acidity
favoring its formation, high acidity depressing or suppressing it." The ad-
dition of an alkali intensifies the violet color; the addition of acid restores
the original red color. The violet color is deepened by standing in the air
after opening the can.
Color changes of red vegetables. Clark gives in his list of indicators that
red cabbage extract is red at /H 2.4 and green at /H 4.5. However, the
results in this laboratory have not agreed with those of Clark. In general
there is lack of agreement in reports of />H at which the pigment of red
cabbage turns blue. There are probably two reasons for this. The antho-
cyanins combine with metals to form salts, the particular metal influencing
the color reactions. Also the color developed at a given />H may depend
upon the time of exposure at that />H. The cabbage itself, when cooked in
water or juice pressed from the cabbage, shows changes at varying reac-
tions, which have varied slightly at different times. This is probably due
to other constituents and their concentration in addition to the red cabbage
coloring. Temperature and time of standing before the determinations were
made also affect the />H.
Usually at a pH of 2.4 to about 4.0 the color is red, showing gradual
changes through blue-red, purple or violet, red-blue, and finally blue. These
changes occur over a rather wide range of />H, the blue developing at
pH 6 or above. The green color develops with greater alkalinity at about
/>H 7 to 9. With still higher concentrations of alkali a yellow or brown
color develops.
If red cabbage is served raw with a salad dressing containing acid it is
bright red or blue-red in color. If cooked in distilled water, it is violet
or violet-blue in color, but often becomes blue after standing a few min-
utes. With a slightly alkaline water the color is blue, for the plant acids
lower the pH of the water. If the water is distinctly alkaline the color
becomes green if cooked about 15 minutes or longer. The addition of a
little soda to distilled water, Experiment 17B, 5, gives a green color unless
the cooking period is exceptionally short. The red vegetables tend to retain
120 FRUITS AND VEGETABLES
their color better when cooked in milk than when cooked in water. Red
onions show the same color changes as red cabbage, but the colors are often
muddy. Red cabbage shows color changes in handling it. When the cut
edges of the cabbage come in contact with the hands or knife they turn
blue. Hands and knives washed in hard water or with soap may have
salts with an alkaline reaction on their surface, but the anthocyanins can
also form compounds with metallic ions.
Beets do not develop the blue or green color, although the color often
contains a considerable amount of blue or purple. Sometimes they turn
from red to yellow when cooked. If the cooked beets are placed in acid,
the red color is often restored after a short time. Blair states that beets
contain two pigments, one being scarlet the other purple. The scarlet
pigment is stable to heat, but the purple one fades. The scarlet pigment
is stable even in the alkaline range as far as pH 9 or, according to Pratt
and Swartout, even at />H 13.0. The color of canned or cooked beets
depends upon the proportion of the two pigments present in the beets.
This is probably an explanation of why cooked beets vary so much in
color, even when cooked under the same conditions of acidity, temperature,
and time. Beets have been produced in which the scarlet pigment has been
increased and which do not lose color when canned at high temperatures.
Metals and anthocyan pigments. The tin salts of the anthocyanins have
been mentioned, but the iron salts are even better known. In general, the
iron salts of anthocyanins are blue. It is known that juice from blue
hydrangeas contains a higher percentage of iron than that from pink
hydrangeas even at the same />H. Some anthocyanins may not combine
with iron or other modifications may occur which prevent or are necessary
for the development of the blue color, for if some anthocyanins are treated
with iron salts the color fades or remains red. Other metals which may
combine with the anthocyanins are aluminum, zinc, and lead. Aluminum
produces about the same colors as iron, although less intense. It seems
reasonable to expect that, if certain salts are present in the vegetable in high
concentration or are furnished by the cooking water or the cooking utensil,
they will modify colors obtained at a given />H in cooking. Also, the blue
color that develops on the cut surface of red cabbage in a short time after
cutting with a metal knife may possibly be due to formation of anthocyanin
salts with the metal.
Lathrop states that both iron and tin are "injurious to fruit pigments.
The compounds of the pigments with the metals become quickly oxidized
on exposure to air, with a marked increase in intensity of discoloration. Tin
turns grapes, cherries, raspberries, and blackberries a deep purple and straw-
berries a pale red. Iron produces dull brownish discolorations. Copper and
aluminum are far less injurious and are therefore used wherever fruit must
come in contact with metal. Copper being somewhat injurious to the color
of grape, aluminum is usually used with grape."
The application of this knowledge comes in cooking fruits, preserves,
REACTIONS OF THE TANNINS 121
and jellies. Since tin cooking utensils are seldom used in household cooking,
this metal would be injurious to color of fruits when used in taking seeds
from berries with tin colanders, or when such fruits are canned in un-
lacquered tin. Iron might affect the color of fruits, if such fruits are
cooked in utensils from which the enamel has been chipped.
Tannins
The term tannin is sometimes used to denote a whole group of substances
having certain characteristics in common. Sometimes it is used to denote
a particular substance, i.e., gallotanic or digallic acid. The former is the
meaning used in the following paragraphs.
The tannins are widely distributed in the higher plants. Some plants
are very rich in them; others contain very little. The amount in the plant
will vary with different years and growing conditions. The tannins are
found throughout the plant, but the woody part, the stems, and rootstocks
are likely to contain larger amounts. They are found in many fruits, espe-
cially during the immature or green stages, and in the seeds of several plants.
Lathrop states that stemming of grapes prior to heating for juice extraction
is advisable to get rid of astringent tannin of the stems which would be
detrimental to flavor.
To some extent the tannin content of fruit is not only dependent upon
environmental influences, but upon inherited characteristics. The New York
Experiment Station has reported a variety of peach called Sunbeam, which
does not turn brown when pared. Kertesz reports its tannin content as
very low, 0.0076 per cent.
Reactions of the tannins. Thatcher states that chemically the "Tan-
nins are either free phenol-acids, or, more commonly, glucosides of these
acids." The structure of the tannins is very similar to that of the anthocyan
pigments. They are divided into two general classes, known as the pyro-
gallol tannins and the catechol tannins. Thatcher has reported the following
characteristic reactions.
PYROGALLOL VARIETY CATECHOL VARIETY
Ferric salts Dark blue Greenish black
Bromine water No precipitate Yellow or brown
precipitate
Leather Produces bloom No bloom
Concentrated sulfuric acid Yellow or brown Red or Pink
Lime water Gray or blue Pink or brown
precipitate precipitate
Haas and Hill summarize the properties of the tannins under eight
headings. Only five will be given here.
1. Tannins are mostly uncrystallizable colloidal substances with as-
tringent properties.
122 FRUITS AND VEGETABLES
2. They give blackish-blue or blackish-green colors with ferric salts,
a fact made use of in the manufacture of ink.
3. In alkaline solution the tannins and many of their derivatives readily
absorb oxygen becoming dark in color.
4. They precipitate gelatin from solution and form insoluble compounds
with gelatin-yielding tissues, a property which enables them to
convert hide into leather.
5. They are precipitated from solution by many metallic salts such as
copper or lead acetates, or stannous chloride.
Astringent qualities due to tannins. The astringent properties give
a slightly bitter taste to some foods, the degree depending on the amount
of tannins present. Thatcher states that "Tannins are of frequent occur-
rence in green fruits imparting to them their characteristic taste. They
nearly always disappear as the fruit ripens." Two explanations are sug-
gested for the disappearance of the tannins in ripening fruit. The anthocyan
pigments may be derived from the tannins, so that as the fruit colors the
tannins disappear; or the tannins may be changed into an insoluble form
and therefore are not so apparent to the taste.
Persimmons contain a very large amount of tannin. Green persimmons
have a bitter, astringent, puckery taste, that is not easily forgotten, once
they have been tasted. Gore's work has shown that most of the tannin of
persimmons is enclosed in cells, which he terms giant tannin cells. By arti-
ficial processing in carbon dioxide, or by ripening, the membrane containing
the tannins becomes hard and insoluble so that the astringent taste is not
evident.
Blue or purple discoloration in English walnuts. English walnuts
are more astringent than other nuts and often develop color changes that
are unattractive when combined with other foods. When they are combined
with apples in a salad they often develop a blackish blue or purple color.
This may come from having prepared the apples with an iron knife, the
acid and enzyme of the fruit acting on the iron to produce ferric salts.
When this small amount of ferric salt comes in contact with the tannin of
the nut and particularly with the skin the purplish color develops. In nut
bread, English walnuts often produce a dark color.
Tannins may produce a gray shade in sugar. Zerban has found
that the color of dark greenish cane juice, which produces a sugar with
a gray shade, may be due to tannins, oxidizing enzymes, and iron. When
the cane is crushed the acid of the juice forms some ferrous salts with the
iron of the roller. Oxidizing enzymes of the juice oxidize the ferrous salts
to ferric ones and they combine with the tannins of the juice. A similar
change occurs when fruits are pared with iron knives and especially when
the juice is left to stand on the knife and it darkens.
Tannins and discolorations in canned goods. Kohman has reported
that the discoloration, a darkening in color, often found in spots in canned
ENZYMES 123
sweet potatoes is due to tannins. The tannin combines with the iron of the
can to produce the dark color. Oxygen is necessary to oxidize the ferrous
iron to ferric, so that, unless oxygen is found in the can, either through not
exhausting all of the air in processing or to a leak in the can, the dis-
coloration does not occur.
Salsify probably contains large amounts of tannic substances. It turns
dark when peeled even if put under water unless a little vinegar is added
to the water to acidify it. Salsify or oyster plant and sometimes other
vegetables such as carrots stain the fingers when they are pared. This may
be due in part to tannins. Lemon juice is effective in removing or lightening
such stains because of its acidity.
Other discolorations with tannins. Brownish or black discolorations
of vegetables in vinegar have been caused by the tannin of the vinegar
combining with the iron of the food. The use of a tannin-free vinegar
does away with this difficulty. Greenish black spots in chocolate ice cream
were traced to the tannin supplied by the chocolate or cocoa and the iron
from rusty spots in the can. In green-colored beer the iron came from
exposed pipes, the tannin from the hops.
According to Atwater, cherry juice, now commercially marketed, when
mixed with gelatin for a molded dessert, sometimes gave a gummy, purplish
precipitate. The precipitate was caused from combination of the tannin of
the juice with the protein, gelatin; the purplish color came from combina-
tion with metals.
Discoloration of pared fruit, considered at greater length in the next
section, is caused by tannin compounds in combination with enzyme action.
Tea. Black tea is darker than green tea because of oxidation of tannins
in the leaf during drying and fermentation. It is also less astringent than
green tea because the tannins are in a less soluble form.
Tannins also give precipitates of calcium, magnesium, and iron tannates,
when these minerals are present in the water. The film on coffee or tea is
from these tannates. When lemon or orange is added to tea, the film usu-
ally disappears, for in acid the tannins often lose the darker color acquired
in an alkaline medium.
Tannins lower the surface tension of water, and the water in which
vegetables containing tannins are cooked is apt to froth or foam.
Enzymes
Enzymes control many of the complex chemical processes of plant metab-
olism. They accelerate reactions which would otherwise take place very
slowly, and though they may initiate the reaction, do not form part of its
final product. Reactions of several enzymes have been mentioned. A large
number of the enzymes are hydrolytic, including the proteinases, lipases,
amylases, and others; but there are also oxidizing and reducing and other
groups of enzymes. Some of the plant enzymes that digest proteins are
124 FRUITS AND VEGETABLES
of slight interest in cookery. An enzyme of the pitcher-plant hydrolyzes
fibrin. Bromelin of pineapple acts on native proteins, its effect being more
often noticed in cookery when uncooked pineapple is added to gelatin,
which is liquefied. Papain of the papaw leaf acts on native proteins. Some
experiments were tried at the Office of Home Economics to utilize the
papaw leaf, the dried powdered leaf, or the extracted enzyme to render
tough meat tender. These did not indicate that papain could be successfully
used in this way, as the enzyme acted on the surface, powdering or pul-
verizing it in only a thin layer even after being in contact with the meat
for several hours, the interior of the meat not being affected.
Oxidizing enzymes. The oxidizing enzymes are concerned with the
processes of oxidation and reduction in the plant cells. They are the cause
of some of the brown color changes in fruits and vegetables when they are
bruised or pared. The principal enzymes that produce the color changes
are the peroxidases, the oxidases (classed as laccases or phenolases by some
authors), and tyrosinase. The internal browning of fruits when injured
involves oxidation as a primary step. But the oxidation requires peroxide
oxygen.
Peroxidases will decompose hydrogen peroxide giving "active" (atomic)
oxygen. They are practically always present in the cells of the higher plants.
Onslow states that fruits and vegetables containing only peroxidases do
not brown when injured. She reports the following of the oxidases. The
oxidases are present in about 63 per cent of the higher plants. A plant
oxidase is made up of three components : ( 1 ) An enzyme, termed oxy-
genase, (2) an aromatic substance containing an ortho-dihydroxy grouping
such as that in catechol, and (3) a peroxidase.
Catechol
\ / H
V
OH
There may be several 'substances with the catechol grouping, i.e., two
hydroxyl groups in the ortho position, found in plants. If the substances
with the catechol grouping are present in plant tissue, but enzymes are not
present, browning of the tissue in injury takes place slowly, but with
oxygenase and peroxidase oxidation occurs rapidly and the material turns
brown on injury. Onslow has reported that apples, apricots, cherries, grapes,
figs, mulberries, pears, plums, peaches, potatoes, and strawberries all con-
tain oxidases. Bananas sometimes contain substances with the catechol
grouping, and sometimes they are absent from the flesh but are found in
the skin. Oranges, lemons, limes, and raspberries do not contain all three
PREVENTION OF BROWNING 125
components of the oxidase system, and the following contain only a peroxi-
dase: blackberries, pineapple, melon, and tomatoes.
Zerban found that the polyphenols in cane juice may be oxidized by
enzymes to a brown color, and to a less extent tyrosin may be oxidized
by tyrosinase, giving a dark color.
Discoloration in pared foods. Pared potatoes, apples and some other
foods will turn dark unless cooked or put under water. The cooking de-
stroys the enzymes, and putting under water prevents the oxygen of the
air from coming in contact with the food. This darkening may be due to
tannic substances which contain a catechol group or oxidases or both. It may
also be due to the flavone and anthocyan pigments, as many of them show the
black reaction typical of tannins since they have the same chemical linkage.
Fresh peaches, pears, apricots, apples, bananas, etc., that are to be used
for a salad and would lose sugar if kept in water may be pared six to
eight hours before serving and kept from turning brown by being dipped
in lemon or pineapple juice and put away in a covered fruit jar.
Although the writer has used lemon and pineapple juice for years to
prevent discoloration of freshly pared fruits, the reason for this, other
than increased acidity, which did not entirely explain the results (pine-
apple juice was less acid and more efficient than lemon juice), was not
known until the work of Balls and Hale was published.
Cruess, Mark, and Quinn state that the oxidase of peaches is not all
destroyed by blanching at 120 to 160F., thus causing internal browning
with the formation of crescent shaped areas often seen in sliced peaches.
To destroy the action of the oxidase of large peach halves requires heating
for 10 minutes at 180 to 200F. These investigators state that fruit
acids such as citric and tartaric are not so effective as hydrochloric acid in
retarding browning. Oxidation was completely held in check by 0.25 per
cent of hydrochloric acid, so that this concentration on the surface of the
peach would prevent browning. Salt and other chlorides will check brown-
ing temporarily; but, after standing in a 2-per cent salt brine, the fruit
must be rinsed to remove the flavor of salt.
Prevention of browning by reducing substances. Joslyn and
Marsh state that the primary oxidation step may be prevented by removal
of oxygen or the addition of reducing substances. And without oxidation
browning does not occur. Sulfites and stannous salts are good reducing
substances. Sulfur dioxide has been used for many years to prevent dis-
coloration. They state that orange juice does not brown at high or low
temperatures when stored in tin cans. The reason given is absence of
oxygen and the reducing action of stannous salts. The addition of ferrous
salts in concentrations of 25 parts per million to the orange juice increased
browning. Ferrous salts were more effective than ferric salts. Nickel,
copper, or stannic salts were without effect, but stannous salts and sulfites
protected against browning. However, after these salts were oxidized,
126 FRUITS AND VEGETABLES
then browning of the juice could occur. The addition of analine or trypto-
phane caused immediate browning.
Balls and Hale found that sulfhydryl compounds, some of which occur
in common foods, prevent browning of apples. Gluthathione and cystein
prevent darkening of the apples even when applied in very dilute concen-
tration. Pineapple juice contains a sulfhydryl compound which is the cause
for its inhibition of development of brown color.
Oxidation and color loss. A type of oxidation that causes fading of
red fruits in canning is explained by Kohman and Sandborn. All fruits and
vegetables use oxygen in respiration, and some oxygen is found within the
fruit or vegetable. The color of strawberries is deadened if they are heated
very rapidly after refrigeration, during which the respiratory processes
have been inhibited. However, if they are heated slowly so that the interior
oxygen is used in respiration the color remains bright.
Sulfur Compounds of Plants
Sulfur compounds are present in the plant in three forms : in the amino
acids of proteins, i.e., cystine, methionine, and others; volatile compounds;
and sulfates.
It is known that a portion of the protein sulfur is readily split off at
boiling or higher temperatures. Peterson found volatile sulfur in clover,
beet tops, blue grass, and milk. This was unexpected, and he suggests that
it may come from two sources, volatile sulfur compounds in the materials
used, or from the. splitting off of sulfur from the protein and the formation
of hydrogen sulfide. He thinks the latter the more probable explanation.
He found a larger percentage of volatile sulfur compounds in plants grown
in a sulfur-rich soil than in those grown in a sulfur-poor soil.
Volatile sulfur compounds. The volatile sulfur compounds are
found in the plants as glucosides. When treated with acid or alkali and
when acted upon by enzymes, these glucosides yield a sugar or some closely
allied carbohydrate and one or more other substances, frequently phenols,
allyl sulfide, or allyl isothiocyanate. Most of the investigations of sulfur-
splitting enzymes have been made upon myrosin. The strong flavor of old
or stored turnips, rutabagas, and cabbage is probably largely due to setting
free of sulfur compounds by enzymes. \Vhen they are cooked, plant acids
are liberated which cause hydrolysis of the volatile sulfur compounds. In
addition, hydrogen sulfide is formed by decomposition of the sulfur com-
pounds by heat.
The odor of many of these compounds is familiar, those of onions and
garlic, cooking cabbage, etc., being typical examples.
Allyl isothiocyanate is found in mustard seed. It is prepared commer-
cially by macerating the seed, the enzyme then splitting off the sulfur of
the glucoside. The oil is then obtained by distillation with steam. Allyl
SULFUR COMPOUNDS 12?
sulfide is found in the onion family, and is prepared commercially from
garlic. The strong flavor of onions, leeks, and garlic depends upon the
concentration of allyl sulfide.
These volatile compounds escape from the food more rapidly with rise
in temperature and breakdown of the plant cells. Hence, the longer onions,
leeks, and garlic are cooked the milder their flavor becomes. Also because
finely minced onion has a greater surface area for volatilization to occur
than when cut in large pieces, these substances volatilize more rapidly
from finely cut pieces. This is why it is preferable to add onion juice, very
finely minced onion, or cooked onion to some foods that are not cooked
long or that do not reach a high temperature, such as hamburger or stuff-
ing for fowl or meat. Large pieces of raw onion in a stuffing produce a
very strong onion flavor, more concentrated in some areas than others,
instead of a subtle, well-blended flavor, for the stuffing never reaches boil-
ing temperature.
The amount of onion and/or garlic added, the fineness of division of
the pieces, and the length of cooking all affect the flavor of the finished
product to which they are added. The flavor of a food like catsup or chili
sauce may be ruined by adding a large quantity of onion or garlic in large
pieces near the end of the cooking process. The same amount of onion
or garlic added in small pieces, or added in large pieces early in the cook-
ing process, could blend with, instead of dominate, the flavor of the other
ingredients.
Sulfur compounds and the cooking of vegetables. It is com-
monly known that long cooking of some vegetables such as cabbage, turnips,
cauliflower, and Brussels sprouts develops strong, disagreeable flavors, and
the eating of these vegetables may cause discomfort and digestive dis-
turbances. The longer cooking and stronger flavor are accompanied by
increased acidity of the vegetable. The length of time of cooking for the
strong flavor to develop varies with the vegetable, whether the cooking is
started in cold or boiling water, and the proportion of vegetable to water.
Simpson and Halliday have determined the total volatile sulfur and
hydrogen sulfide evolved when cabbage and cauliflower are cooked for
different lengths of time. They found that the most acceptable product is
obtained when winter cabbage is boiled 7 to 8 minutes, and spring cabbage
5 minutes. Cauliflower required 8 minutes to become tender. They con-
clude that with prolonged cooking the decomposition products of sulfur
compounds increase, and that these products produce the strong taste and
odor associated with cabbage and cauliflower.
Simpson and Halliday report that the amount of hydrogen sulfide in-
creases from the fifth to the twentieth minute of boiling cabbage, and the
total volatile sulfur between the seventh and thirtieth minutes. Cauliflower
gives off more volatile substances in the same period than cabbage. Masters
and Garbutt have found that the amount of sulfide increases up to a cer-
128 FRUITS AND VEGETABLES
tain point and then decreases, becoming fairly constant. Kohman states that
in corn the amount of hydrogen sulfide evolved is greater during the first
half hour and decreases with each succeeding half hour.
Shilling in determining the amount of hydrogen sulfide formed in cook-
ing cabbage finds that it varies from 1 to 7 milligrams per 300 grams of
fresh cabbage. The wide variation depends upon the amount of green
compared with the white, the speed of cooking, the length of time of
cooking, and the temperature involved in the method, i.e., boiling in water
and the pressure cooker.
Bigelow has reported that the black spotting on the corn around the
edges of the can in canned corn is due to the formation of hydrogen sulfide
in processing. The amount of sulfide is very small and there is no objection
to it except from appearance. Stevenson states that iron sulfide is formed
to a greater extent in canned peas than in canned corn. It is not so notice-
able in peas on account of their color. In peas it is deposited as scales that
break up easily in shipping and handling.
Flavor
The flavors of fruits and vegetables are due to several constituents, sugar,
organic acids, mineral salts, and aromatic compounds.
Sugar is found in fruits and vegetables. Beets, carrots, onions, peas, and
other vegetables contain appreciable amounts. In vegetables like peas and
corn the sugar is deposited as the insoluble carbohydrate, starch, in the
mature seed. Immature peas and corn deteriorate rapidly in sugar content
after they are gathered. Kertesz reports that starch increases and sugar
decreases in stored fresh peas, but the sugar loss is not due to the trans-
formation of sugar to starch. It is suggested that the apparent increase of
starch content is because of loss of other constituents; and, whereas the
loss of the sugar is not satisfactorily clarified, it may be consumed in
respiration. Losses in sugar content can be prevented by inactivation of
the respiratory enzymes by blanching, cooking, or storing near freezing
temperatures.
The vegetables with a fairly high sugar content usually have a sweeter
flavor if steamed or if just enough water is used to cook them and it is
evaporated to dryness at the end of the cooking period. Even mild-flavored
onions may be sweeter and better flavored if the water is evaporated than
when an excess is left. But there seem to be some exceptions to most rules,
and the choice of method of cooking is often a matter of judgment or
circumstance. More could be written about flavor, but it has been men-
tioned so often in connection with different constituents of fruits and
vegetables that a great deal would be repetition.
A combination of sugar, acids, and aromatic substances gives flavors that
render fruits and vegetables palatable and attractive food products.
EFFECTS OF ALKALIES, ACIDS, AND CALCIUM 129
Aromatic compounds. This classification is not given as a plant
chemistry one, but as a group to include all substances that may give
characteristic odor and thus flavor to foods.
Many of the aromatic compounds are esters, like amyl acetate, which
gives a characteristic odor to pears and is called "pear oil." The odor of
pineapple is due to methylbutyrate, which is designated "pineapple-oil."
Isoamyl isovalerate produces the characteristic odor of apples.
Thatcher includes all the substances that give characteristic odor to
plants under the term "essential oils and resins." Some of these substances
are terpenes, alcohols derived from terpenes, the phenols, and sulfuretted
oils. Oils of lemon, peppermint, cinnamon, clove, lavender, and others are
classified as essential oils.
Allyl isosulfocyanide, oil of mustard, and allyl sulfide, oil of garlic, con-
stitute the best known of the oils containing sulfur.
Tannins impart an astringent, bitter flavor to some foods.
Cellulose
Cellulose forms the structural, fiber, or woody part of the plant. Other
substances such as pectic substances may occur in combination with cellu-
lose. In the young plants or the new growth of older plants the cell walls
are at first yielding. As they mature, they grow more resistant and may
change physically and chemically, their function becoming more specialized
with the occurring changes. In tree trunks some cell walls become woody
or lignified. Doree and Barton-Wright state that the stone cells distributed
throughout the flesh and particularly near the core of pears are lignified
cellulose.
Cellulose is a carbohydrate. It is found in plants in several forms. There
is no unanimity of opinion regarding its definition, although the cotton fiber
is always taken as a standard cellulose product.
Hemicellulose, wood cellulose, and gelatinized cellulose are names given
to different forms of cellulose. Probably each group includes several prod-
ucts. Schorger defines hemicellulose as "A polysaccharide soluble in dilute
alkalies and convertible into simple sugars by heating with dilute acids
at atmospheric pressure." He adds that a hemicellulose in the natural state
should be insoluble in boiling water.
Effects of alkalies, acids, and calcium on the structural or
woody part of fruits and vegetables. Ammonia and sodium bicar-
bonate added to the water in which vegetables are boiled, or ammonia or
ammonium carbonate added to water in which vegetables are steamed,
causes them to soften in a shorter time than if these substances had not
been added. With longer cooking the vegetable becomes mushy and dis-
integrates. The disintegration begins with the surface layer of the food,
and its depth depends on the length of time of cooking and the size of
the piece of food.
130 FRUITS AND VEGETABLES
If vinegar is added to the water in which vegetables are cooked the
effect is opposite from that of sodium bicarbonate : a firmer and more solid
texture is obtained and the vegetable requires longer to cook. In cooking
vegetables like cabbage and spinach the amount of calcium and magnesium
salts found in the water seems to have little effect upon the texture or the
length of time for cooking.
The pulp and white part of the rind of watermelon as well as the pulp
of muskmelon or cantaloupe, and perhaps other foods, can be made very
firm and brittle or woody if soaked in saturated calcium hydroxide (lime)
water. The longer they are soaked the harder and firmer they become if
the water is kept saturated with lime. Five to six hours' soaking is usually
sufficient to produce enough firmness to prevent shriveling when cooked
in sirups for preserves or pickle. The melon pulp may be cooked in water
until transparent and tender, then put in lime water to harden, and finally
cooked in a sirup. Or cooking first in only water does not prevent harden-
ing of the pulp by calcium. The few times that cucumbers have been soaked
in lime water either slight or no hardening occurred. But other calcium
compounds such as calcium chloride do produce hardening in pickles.
Pickles. Cucumber pickles are seldom made in class work; but why
brined pickles spoil is a perennial question. Rahn has offered a solution of
the difficulty. An abstract of his work follows.
The inside of the cucumber is free of bacteria, but the brine into which
the cucumbers are placed contains several thousand bacteria per cubic
centimeter. There are many different kinds of bacteria present in the
beginning but with the strength of brine maintained most of them die.
However, a few kinds that thrive in the brine survive. Fresh brine con-
tains no food for bacteria. But with placing of the pickles in brine, or the
formation of brine by adding dry salt to cucumbers, small amounts of
sugar and other bacterial food are dissolved from the cucumbers as they
shrink. Hence bacteria that can tolerate salt grow and decompose the sugar.
The resulting decomposition products of the sugar are acid and gas. The
gas produces froth. The acid, probably mostly lactic, is very important,
for the keeping of the pickles depends upon it. The concentration of the
acid is rather high when frothing ceases, varying from 0.6 to 1.2 per cent.
The acid is a fairly good disinfectant and practically all bacteria in the
brine are killed.
In addition to bacteria, yeasts are present in the brine; but because they
need oxygen they grow principally on the surface. The scum yeast feed
on the acid of the brine and decompose it, thus decreasing the quantity of
acid in the tank or container. If scum grows long enough, all the acid is
destroyed and then the pickles become slippery, soft, and mushy. It is better
not to stir the pickles too much after they are in the brine, for the acid
tends to stay at the bottom of the container and the yeasts grow at the
surface.
EFFECT OF SUGAR ON THE FIRMNESS OF FRUIT 131
There are two periods when the acid is low, and these stages are the
periods of greatest danger in fermenting pickles. The first stage is before
fermentation has started and no or little acid has been formed ; the second
is after the acid has been used up by scum yeast, for spoilage only occurs
when the acidity of the brine is sufficiently low. The slipperiness and soft-
ness are caused by so-called potato bacteria, which resist the salt well
but do not tolerate acid. Because oxygen is necessary for their growth and
the bacteria only grow at the surface, the pickles protruding from the brine
become soft. These potato bacteria can cause great loss and damage before
a concentration of acid great enough to delay their growth is formed.
A single potato bacterium, if all conditions are favorable, produces from
10 to 100 million new bacteria in 24 hours.
Hence, to prevent spoilage all pickles should be kept under the brine.
Some acid or vinegar can be added with the brine to prevent spoilage.
It has been interesting to see that this has been advocated for commercial
practise since Rahn's work was published. Other methods of preventing
growth of the yeast are to keep the container in the sunlight or irradiate
with ultra-violet light, both of which are not practical in the home. After
fermentation is complete, that is, after frothing has ceased, oil or paraffin
may be used over the surface of the brine. Since the oil is rather difficult
to wash from the pickles, paraffin is preferable.
Crisping pickles. Calcium chloride is used to make pickles crisp or firm.
It is used either in the last soaking water, when the brine is being removed,
or added directly to the sweetened vinegar. The proportion used is one
pound per barrel of pickles.
The hardening may come from the calcium combining with the cellulose
or it may combine with acid of the pickle or melon or be deposited as
calcium salts in the food. Some factors other than the ones mentioned may
cause the hardening.
The effect of sugar on the firmness of fruit. The effect of sugar
of course varies somewhat with the amount used in proportion to the
quantity of fruit. Osmosis occurs when a sirup has greater sugar concentra-
tion than that of the fruit to which it is added. The vapor pressure of
the sirup solution is lower than that of the fruit so that water passes
from the fruit to the sirup. This transfer from a region of high concen-
tration to a low one is called osmosis. If a membrane separates the regions
of high and low concentrations it is dependent upon the membrane whether
all the dissolved constituents of a solution can pass through the membrane.
With a semi-permeable membrane only the water can pass through the
membrane. Without discussing the possible role of the membrane in osmosis
or the osmotic pressure that may be produced, it is sufficient for the purpose
here to state that as the permeability of the membrane increases larger
and larger ions or molecules dissolved in the water may pass through the
membrane. The skin and cell walls of the fruit serve as membranes. These
132 FRUITS AND VEGETABLES
membranes in the different fruits seem to have a greater or a lesser permea-
bility to sugar.
When cooked in a sirup some fruits tend to keep their shape, some be-
come mushy, some shrivel, and others tend to collapse or flatten out. For
instance, sweet apples tend to stay whole whether cooked in sirup or in
water, whereas sour apples have a greater tendency to break up during
cooking. In general, the fruits tend to stay whole better if cooked in a
sirup. For purees the fruit is cooked in water and the sugar added later.
Cooking seems in most instances to increase the permeability of the fruit
membranes to sugar. Some apples, some plums, and most berries can be
cooked directly in the sirup without noticeable toughening of the fruit.
Peaches, apricots, most apples, and most plums absorb sugar satisfactorily.
Lathrop states that the firm texture of the cherry skin and of the peach
and blackberry flesh retards penetration of the sugar during cooking. On the
other hand, a fruit like Keifer pears is dehydrated if cooked directly in a
sirup and becomes shriveled, tough, hard, and rubbery. It is necessary to
soften the fruit by cooking and increase its permeability to sugar before
the sugar is added. It is of course possible that many changes other than
increasing the permeability of the fruit to sugar occur when the fruit is
cooked in sirup. Later work has shown that fruit like Keifer pears and
quinces can be cooked by adding the sugar directly to them without pre-
liminary cooking. But it is necessary to start with an excess of thin sirup
and cook slowly to evaporate the excess liquid, as the sugar penetrates the
fruit. So long a time is required that the method is not practical. The fruit
becomes more transparent in appearance. It may be that the sugar has
some effect on the cellulose.
In fruits like strawberries and seeded sour cherries, and particularly if
they are heated rapidly in a sugar sirup, flattening occurs. If a large number
of cell walls are broken the fruit becomes mushy. Time is required for
sugar to pass through the cell walls of fruits. If osmosis has not progressed
far enough, i.e., if the concentration of the sugar within the berry is not as
great as in the sirup surrounding it, the berry floats when canned.
In pickling, shriveling can be prevented by heating the pickling material
slightly and increasing the concentration of the sugar gradually, allowing
about 24 hours or more to elapse before the next addition of sugar. But
fermentation is more likely to occur when preserves are treated this way.
It is a good practise to add the sugar directly to fruits like strawberries
and cherries and let them stand over night. The fruit loses water, shrinks
somewhat, and becomes slightly tougher. When heated slowly, and if neces-
sary removed from the heat for a few minutes before boiling commences,
there is time for the sugar to penetrate into the interior of the berry, the
fruit is plump and will not float when placed in the container. In the
commercially vacuum-processed berries, floating in the can is prevented by
adding the berries, to which part of the sugar has previously been added,
to a hot sirup, but further heating is not continued until the berries have
SOME INVESTIGATIONS ON POTATO QUALITY 133
stood for a few minutes. By producing a vacuum, the greater pressure
within the berry tends to puff it up; by breaking the vacuum, flattening
occurs. In this way the process of osmosis is helped.
Strawberries and the sour cherries develop a strong flavor when boiled
for a long time. Hence time must be allowed for the sugar to penetrate
into the fruit before the boiling point is reached. Boiling should be rapid,
and the quantity of fruit used in a batch small. The popularity of sun
preserves for certain fruits is due to osmosis being slow and complete.
If the fruit is heated the heating period is very short, so that strong flavors
are not developed, less sugar is inverted and caramelized, and the aromatic
substances are not lost to such an extent as in long cooking.
Since strawberries usually contain about 90 per cent water, it seems a
better practise to add the sugar directly to the berries, for not as long a
time is required to cook the berries to the concentration desired. When
water is added to the sugar to make a sirup it is necessary to evaporate the
water used in the sirup as well as a part of that contained in the fruit.
Increasing the proportion of sugar to fruit also lessens the time required
to reach a definite concentration of the sirup, so that the preserves do
not develop as strong a flavor. When 1^2 pounds of sugar are used with
a pound of strawberries only a short time of cooking is required for the
sirup to reach a temperature of 103C, which gives a sirup containing 60
per cent of sugar. See Table 10.
Potatoes
What constitutes quality in potatoes? For baking and boiling it is
usually accepted that the best potatoes are those that yield a white, com-
paratively dry, and mealy texture. The homemaker does not like for
boiling a potato that sloughs off badly during cooking, though this often
occurs with some of the best baking potatoes. For deep-fat frying, dicing
for salad, and other purposes a potato that gives a waxy and firm con-
sistency is considered best.
Some investigations on potato quality. It is rather commonly be-
lieved that to have mealy potatoes the starch content should be high and
that the swelling and bursting of cell walls during cooking produces the
white, fairly dry, flaky appearance. Sweetman states that the starch grains
do not swell sufficiently to burst but the cooking renders the starch
granules readily separable. That ease of cell separation is one of the
causes of mealiness is unsubstantiated by other investigators. Whittemore
and Juschke decided that potatoes were more mealy when fertilized with a
high rather than a low quantity of potash (potassium carbonate).
Cobb states that the parts of the tuber having the greatest concentration
of starch are mealiest when cooked. The rank in descending order is cortex,
external medulla, and internal medulla. Cobb in a series of investigations
covering 5 years found that baking gave more mealy potatoes than boiling.
134 FRUITS AND VEGETABLES
Baked potatoes often lost 25 per cent of their weight by evaporation,
whereas boiled ones lost none.
Environmental factors. Cobb concluded that if proper cultural con-
ditions were given any type of soil may grow good potatoes. His studies
showed that temperature during growing and variety were the most
important factors affecting potato quality. A low-average temperature
favored better quality. This suggests that one reason why Maine and
Idaho are noted for their potatoes is the low-average temperature during
growth of the potatoes. Small, immature, or ill-shaped tubers were ob-
served to have poor quality.
Stevenson and Whitman state that a variety producing good-quality
potatoes under certain conditions may produce poor ones under other condi-
tions, but a good-cooking variety tends to maintain better quality over a
wider range of conditions than a poor-cooking quality.
Starch granules. It is possible that two factors determining whether
a potato produces a mealy or waxy consistency when cooked are the size of
the starch granule and its phosphorus content. See Starch, Chapter XI.
Large granules swell and gelatinize at a lower temperature than small
granules. Thus, potatoes giving a dry, mealy texture may have a compara-
tively larger percentage of large granules. Smaller granules are supposed
to have a higher phosphorus content than large ones, and the paste-forming
qualities of starch are increased when the starch is combined with phos-
phorus. If paste-forming qualities mean increased adhesiveness, then waxy
potatoes may have either smaller granules or a higher phosphorus content
or both.
Storage temperature. Wright et al. found that the storage tempera-
ture affected the quality of the cooked potatoes. They stored Irish Cobbler
potatoes harvested August 3 for 8 weeks at the following temperatures:
32, 36, 40, 50, 60, and 70F. In general potatoes stored at 40
were considered fair in quality when cooked; those from storage at 32
and 36 were poor; those from 50 good; those from 60 very good,
and those from 70 good. The baked and boiled products from potatoes
stored at 40 were slightly sweet and watery; those from 36 storage were
inclined to be soggy or watery, with a distinctly yellow color and sweet
flavor; those from storage at 50, 60, and 70 possessed no undesirable
sweet flavor and were of mealy texture and cream in color.
Potato chips. The most important factor in making potato chips ap-
pears to be the sugar content of the potato. With a high sugar content the
chips become too brown, with production of a more or less disagreeable
astringent flavor, before they are sufficiently cooked. The concentration of
sugar increases in potatoes stored at a low temperature. At ordinary tem-
peratures the sugar is used up in respiration ; at lower temperatures metab-
olism is retarded but su^ar production by enzymes proceeds, so that sugar
accumulates.
COOKING OF DRIED LEGUMES 135
Peacock and Brunstetter have reported a very simple test for predeter-
mining the cooking value of potatoes because of accumulated sugars. One
cubic centimeter of a saturated aqueous solution of picric acid and 1
cubic centimeter of a 20-per cent sodium carbonate solution are placed in a
test tube. To this is added a piece of potato of definite length cut with a
cork borer. The solution is heated carefully to prevent boiling over for
1 minute. If the solution does not become much darker it indicates that
the potato has little sugar and is suitable for both chips and "French
fries." With increasing sugar content the solution becomes darker and
darker when time of heating and size of piece of potato are kept stand-
ardized. The darkest shade given by Peacock and Brunstetter is a dark
garnet-brown; but Swalley tested some potatoes that gave shades two
degrees darker in color than dark garnet-brown, the darkest being nearly
black. Potato slices fried for a definite time in fat at a definite tempera-
ture become browner and browner as the sugar content increases and give
perfect correlations with the picric acid test. In general Swalley found
that the longer the potatoes were stored at 32F. (storage was from
11-14 to 12-15), the longer the time required for storage at room tempera-
ture (those stored at 32 for 31 days required 45 days at room tempera-
ture) before good chips were obtained.
Wright et al. found that potatoes stored at 32 and 36 were not suitable
for French fries, as they browned too quickly and had a burned flavor.
To some extent this was also true of potatoes stored at 40. As the storage
temperature increased the time necessary for cooking increased. Potatoes
stored at 60 and 70 gave fries of attractive golden-brown color, mealy
texture, and good flavor. Similar results were obtained with chips.
Preparation of chips. Because it is difficult or impossible to slice the
potatoes evenly by hand, they should be cut with a slicer. If salt is added
to the soaking water the slices are partially dehydrated during the soak-
ing; thus a shorter time is required for cooking and no addition of salt
is necessary after cooking. For T /[ pound of potato and YZ cup of water
about 8 grams of salt are required.
Cooking chips. The cooking time and temperature are dependent to a
certain extent on the quantity of potatoes added to a given amount of fat.
For ]/<{ pound of slices about 3 minutes are required when the initial
temperature of the fat is 190C. and the quantity of fat is about 2 to
2^2 pounds. Smaller quantities of potatoes cook in a shorter time. The
chips are done when bubbling of the fat ceases, which indicates the major
portion of the water has evaporated.
Cooking of Dried Legumes
Different varieties of beans and peas belong to the legume family. The
dried legumes commonly used for food are navy, lima, kidney, soy, other
136 FRUITS AND VEGETABLES
varieties of beans, lentils, and dried peas. The dried legumes contain less
moisture than the fresh ones. In cooking, the moisture lost by drying is
replaced and water is absorbed. The legume is softened. This requires a
longer period than for fresh legumes, so that the methods of cooking that
shorten the cooking process are more important than for fresh vegetables.
Effect of mineral content of the water upon cooking of dried
legumes. Huenink and Bartow in trying to determine why the quality
of canned products from some factories was always superior to those of
others found that the mineral content of the water affected the softening
of dried beans in cooking. Using a sirup and distilled water in canning
beans, they found the product very tender and one that would grade
strictly fancy on the market. When to the sirup, distilled water, and beans,
calcium chloride was added, using lots with 100, 200, 300, 400, 500, 600,
and 1000 parts per million parts of water, the hardness of the processed
beans increased with increasing calcium chloride, the ones with 1000 being
nearly as hard as uncooked beans. The series with 100 to 200 parts of
calcium chloride were hard and tough and would grade standard on the
market and be called underprocessed. Continuing their work they tried
the following salts :
Calcium chloride CaCl2
Calcium sulfate CaSCX
Calcium bicarbonate Ca(HCOs)2
Magnesium sulfate MgSO 4
Magnesium bicarbonate Mg(HCO 3 ) 2
Sodium carbonate Na2COa
Sodium bicarbonate NaHCO 3
They found that the calcium and magnesium salts hardened the beans
whether as chlorides, sulfates, or carbonates. The calcium and magnesium
bicarbonates had a hardening effect but the results were not as consistent
as with the other salts.
Both the sodium carbonate and sodium bicarbonate gave a softening
effect, and with larger quantities the beans appeared over-cooked.
The National Canners Association has reported that calcium and mag-
nesium salts harden beans and peas during cooking, having a greater effect
upon the beans than on the peas. String beans and corn do not seem to
be affected, nor are beets affected up to 350 parts of magnesium or calcium
per million parts of water, but the salts of hard water combine with the
soluble oxalates of the beet to give a white coat on the surface of the beet.
Van der Marel, investigating the effect of various salts, bases, and acids
upon the softening during cooking of dried peas, has reported the following
results. Using a "good cooking" variety of peas, and cooking for 1 j/2 hours
he determined the percentage remaining hard at the end of the cooking
period.
HARD WATER
137
TABLE 18
COOKING DRIED PEAS (Van der Marel}
Type of water and substance added
Percentage of peas remaining hard
after cooking IX hours.
Distilled water
Amsterdam city water . . .
Formic acid 0.01 M
Calcium chloride 0.01 M .
Sodium carbonate 0.01 M
5
14
68
100
2
With another variety of pea more difficult to cook he obtained the fol-
lowing results after soaking 24 hours and boiling 2 hours.
TABLE 19
COOKING DRIED PEAS (Van der Mar el]
Type of water and substance added
Percentage of peas remaining hard
after soaking 24 hours and boiling
2 hours.
Distilled water
Amsterdam city water
Sodium carbonate 0.01 M . . . .
Ammonium hydroxide 0.01 M
43
67
4
Van der Marel decided that the softening effect was due to action on
the pectic substances of the peas and that anything that made the pectic
substances more soluble had a softening effect in cooking.
The results of Huenink and Bartow and of Van der Marel show why
some waters are not desirable for cooking dry legumes. With increasing
hardness of the water the hardening effect on the vegetable is more notice-
able. Some housewives have found this out from experience. The writer
remembers her grandmother's insisting that dried beans should be cooked
in cistern water, because they cooked more quickly than in the well water
which was permanently hard.
Hard water. Hard water contains salts of calcium, magnesium, and
sometimes iron. Hardness of water is designated as temporary or perma-
nent. Water containing calcium and magnesium bicarbonates is termed
temporary hard water since the heating of the bicarbonates decomposes
them and carbonates are formed which are deposited as crusts on the inner
part of the tea kettle or cooking utensil. Such waters are rendered less
138 FRUITS AND VEGETABLES
hard by boiling. Permanent hard water contains the sulfates of magnesium
and calcium. Some water is both temporarily and permanently hard.
Softened water, which is used a great deal at the present time, has the
calcium and magnesium replaced by sodium. The author has noticed that,
since softened water is used in the Home Economics building at Iowa
State College, fresh green peas never become hard as they sometimes did
with the old permanently hard water and that the difference between the
time required for cooking dry beans not soaked and those that are soaked
is very much shorter.
The pectic substances of bean coats. Snyder noticed that if the seed
coat of pea or Great Northern beans was injured or scarified, the beans
swelled in soaking and cooked in a shorter time. Next she noticed that
entrance of water into the beans is not uniform over the entire surface of
the bean but most of the water entered through the micropyle and germinal
area. Substances that dissolved the pectic substances shortened the soaking
and cooking time. Beans with very hard skins neither soaked nor cooked
satisfactorily and contained a higher percentage of pectic substances than
skins of beans that soaked and cooked easily. The major portion of the
calcium of beans was found in the seed coat.
Snyder's results with calcium and magnesium salts, with acids, and with
soda substantiate those of earlier investigators, with the exception that
oxalic acid, which cannot be used in preparation of edible products, did
not depress absorption of water. Oxalic acid would render the calcium
salts insoluble.
Snyder found that j/g teaspoon of soda per pint of water was sufficient
for soaking to shorten the cooking time, except with one very hard water.
If the beans were soaked in water at 120F. the maximum amount of
water was absorbed in 6 hours. Molasses and tomato juice had an effect
similar to that of acids but could be added without injurious effect after
the beans were cooked. Beans that cooked rapidly on top of a burner also
baked satisfactorily.
Masters's results with legumes. Masters, using London tap water
(temporary hardness 12 parts per 100,000 parts of water and permanent
hardness 5 parts per 100,000 parts of water) and cooking butter beans,
found that soaking made little difference in time required for cooking,
but that soaking with sodium bicarbonate in the soaking water did shorten
the cooking time. Distilled water gave a shorter cooking time than tap
water. Masters also determined the soaking and cooking losses of total
solids. It is interesting to note that soaking with soda in the water gave
not only a shorter cooking period, but also a slightly decreased loss of
total solids. However, there was only a very slight difference. This was
with the percentage of soda that she considered to give the best cooking
results, 1 per cent (equivalent to about ^s teaspoon of soda per cup of
water). With larger amounts of soda than 1 per cent, greater losses due
to disintegration of the beans occurred. With a small amount, 0.25 per
CLASS RESULTS WITH NAVY BEANS 139
cent, the cooking time was shortened but the total loss of solids was slightly
higher than for the other methods of cooking. Losses were also high when
large amounts of soda were used in the soaking instead of the cooking
water. When other types of beans were substituted for the butter beans,
the results were similar, although the cooking time might be longer or
shorter according to the nature of the beans, and the cooking losses higher
or lower, varying with the thickness of the skins of the beans. The loss of
solids during cooking of the butter beans was about 10.5 to 11 per cent
if beans were not soaked. If beans were soaked before cooking the total
loss was about 12.5 per cent.
One of the methods recommended by Masters for cooking beans is to
add soda to the soaking water and salt to the cooking water. She found
that discarding the soaking water gave no greater cooking losses than when
it was retained and the beans cooked in the water in which they were
soaked.
Class results with navy beans. The experimental class results for
several years at Iowa State College show that, although some navy beans
cook in a very short time, the majority require about the same time, which
is close to the average given in the following tables. Some require longer
cooking. To show this the minimum and maximum time as well as the
average are given in the tables. The beans were washed and added to 1 pint
of boiling water. If the water evaporated to dryness, boiling water was
added. The soaked beans stood over night, usually 15 to 24 hours. All the
figures are for 15 or more tests. The water is quite hard, averaging about
340 parts of carbonate per million parts of water. The mineral content
as carbonate is as follows:
CaCO 3 240 parts per million parts of water.
MgCO 3 100 parts per million parts of water.
For an end point in cooking the beans were cooked so that they would
be as whole as possible yet soft all the way through. A common household
way of testing when beans are done is to stick them with the point of a
sharp knife or fork. This was the test used, but the experiments being done
by students through different quarters give differences of opinion as to when
the beans were done. For example, the minimum time for beans cooked
with soda in tap water is shorter than the minimum time for beans soaked
with soda in distilled water, but the averages are reversed.
Soda may be added to the cooking water and not discarded. This was
tried in class, but the beans became mushy on the outside and disintegrated
while the center was still hard.
In all varieties of beans, cooking with the vessel covered gives a shorter
cooking period than cooking uncovered. This may be due to the cooling
effect by evaporation of the water at the surface and possibly will not occur
with a large quantity of beans and water.
140
FRUITS AND VEGETABLES
TABLE 20
CLASS RESULTS FOR COOKING NAVY BEANS BY DIFFERENT METHODS
Method of cooking
Weight
of un-
cooked
beans
grams
Weight
of
soaked
beans
grams
Weight
of
cooked
beans
grams
Tap water
Minimum 50
Maximum 50
Average
Distilled water
Minimum 50
Maximum 50
Average
Soaked in tap water
Minimum 50
Maximum 50
Average
Soaked in distilled water
Minimum 50
Maximum 50
Average
Soaked in tap water, y$, teaspoon of
soda added to soaking water, but
no soda in cooking water
Minimum 50
Maximum 50
Average
Soaked in distilled water, soda yi
teaspoon added to soaking water,
no soda in cooking water. Cooked
in distilled water
Minimum 50
Maximum 50
Average
Salt J4 teaspoon added to tap water
Minimum 50
Maximum 50
Average ,
Soda y& teaspoon added to tap water
Boiled 10 minutes. Discarded
Minimum 50
Maximum 50
Average
98
106
100
98
105
101
95
106
99
96
104
99
92
134
110
91
122
111
102
131
116
105
133
118
100
136
116
111
142
121
91
116
100
95
145
118
REFERENCES 141
Soaked beans are lighter in color and less strong in flavor than the
non-soaked ones.
Lima beans. Although the work with lima beans has been limited
in extent in comparison to that done with navy beans the results have been
similar to those obtained with the latter.
Soaking to shorten the cooking period must continue until the beans have
absorbed enough water to weigh nearly double their dry weight. When
boiling water was poured over the lima beans and left to stand, swelling
occurred more rapidly than when cold water was used. The time required
for soaking with cold water is 7 to 8 hours or longer, but with the boiling
water 4 to 5 hours is usually sufficient.
Pinto beans. Greenwood found that the degree of hardness of the water
is the most important factor to consider in cooking beans. Satisfactory
results were obtained by any method with very soft water, and no method
was entirely satisfactory with very hard water. Boiling water 20 to 30
minutes to precipitate the calcium and magnesium salts before using for
cooking the beans was beneficial. In using hard water better results were
obtained if it was boiled gently and the vessel was well covered to avoid
evaporation of water, thus preventing the necessity of adding more water
and increasing the total salts added. For the shortest cooking period the
beans should be soaked in hot soda water (0.5 per cent solution), \ l /2 tea-
spoons to 5 cups of water.
Dried soybeans. The use of soybeans for human consumption is con-
stantly increasing, both the green and dry varieties being used to a greater
extent than formerly. Some varieties are nearly impossible to cook but va-
rieties easier to cook are used for edible purposes.
Work with dry soybeans indicates that soaking over night in cold water
nearly halves the cooking time. Addition of soda to the soaking water fur-
ther shortens the cooking time. But pouring boiling water over the beans
and letting them soak in this water for 3 or 4 hours results in the shortest
cooking time.
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Simpson, J., and Halliday, E. G. The Behavior of Sulfur Compounds in Vege-
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Snyder, E. B. Some Factors Affecting the Cooking Quality of the Pea and Great
Northern Types of Dry Beans. Research Bull. 85. Agri. Expt. Sta., Neb.
(1936).
Steinbarger, M. The Effect of Salt upon the Loss of Iron in Cooking Vegetables.
Unpublished Thesis (M. A.) University of Missouri, Columbia, Mo. (1923).
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Stevenson, A. E. Discoloration in Canned Foods. Canning Age 5: 951 (1924).
Stevenson, F. J., and Whitman, E. F. Cooking Quality of Certain Potato Va-
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Sweetman, M. D. The Physico-Chemical Changes Produced by the Cooking of
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Thatcher, R. W. Chemistry of Plant Life. McGraw-Hill Co. (1921).
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FRUITS AND VEGETABLES
Experiment 17.
A. To determine the effect of different methods of cooking on the color of
green vegetables.
Use Y pound (56 grams) of spinach, lettuce, Brussels sprouts, green beans
cut in 1-inch strips, or green asparagus. Use 1 cup of water. Cook 10 to 25
minutes, the time depending upon the vegetable used, but decide upon the
length of time the vegetable is to be cooked before experiments are started.
Save the water left from each experiment to compare for color and flavor.
Notice the texture of the vegetable.
1. Pour boiling water over the vegetable. Cook covered for the length of
time agreed upon.
2. Repeat Al, but cook uncovered.
3. Add salt to the cooking water. Use ^4 teaspoon per cup of water. Cook
uncovered and start in boiling water.
4. Cook uncovered in boiling distilled water.
FRUITS AND VEGETABLES
145
5. Cook uncovered in boiling distilled water to which 1/16 teaspoon of soda
has been added.
6. Cook uncovered in boiling distilled water to which Y^ teaspoon of vinegar
has been added.
7. Cook in a steamer.
8. Cook in a pressure cooker, 10 minutes at 15 pounds pressure.
9. Cook in milk.
If desired, some of the cooking water may be tested for iron and phosphates.
In which case is the green color of the vegetable best preserved? Is there
any difference in the texture of the vegetables with soda and with vinegar
added?
Vegetable used:
Time of
cooking
Color of
vegetable
Texture
Color and
amount of
water
Flavor
Results and conclusions.
B. To determine the effect of different methods of cooking on the color of
red vegetables.
Use red cabbage if it can be obtained. If it is not obtainable, use red onions
or beets. Repeat the directions under A for cooking.
Vegetable used:
C. To compare the effect of different methods of cooking on the color of
yellow vegetables.
Use carrots or squash. Repeat the directions under A for cooking. Do not
confuse caramelization of sugar by alkali with pigment change of color.
Vegetable used:
Compare the effect of acid and alkali on the green, red and yellow pigments
found in vegetables. What is the effect of the soda on the texture? Of the
vinegar? Which is the preferable way of cooking each of the different colored
vegetables ?
Experiment 18.
To determine the effect of alkaline and neutral water upon the color of
white cereals and vegetables.
la. To \y$ cups of boiling water add /4 CU P f washed rice. Cook until
tender. Add more boiling water if necessary during cooking. Remove about
YZ of the cooked rice from the sauce pan and drain.
\b. To the rice remaining in the sauce pan from la, add % to 1/16 of a
teaspoon of cream of tartar. Cook 2 minutes and drain.
2a. To \y$ cups of boiling distilled water add l /4 cup of rice washed in
distilled water. Add boiling distilled water during cooking if necessary. When
the rice is tender remove about l /2 of the cooked rice from the sauce pan and
drain-
146
FRUITS AND VEGETABLES
2b. To the rice remaining in the sauce pan from 2a, add l /% to 1/16 tea-
spoon of soda. Cook 2 minutes, then drain.
3. Add half a white onion to 1 cup of boiling tap water. Cook until tender.
Save the other half of the onion for 4.
4. Repeat 3, but use distilled water. Cook the same length of time as 3.
5. Repeat 3 and 4, using flowerlets of cauliflower or white cabbage.
Results and conclusions.
Experiment 19.
To determine the effect on the flavor and tenderness of a strong-flavored
vegetable cooked by different methods and for different lengths of time.
Use Y% pound (56 grams) of cabbage, Brussels sprouts, or turnips cut into
pieces. Onions can be used but they become milder with longer cooking. Add 1
pint of boiling water. Cook until tender.
A. Methods of cooking.
1. Cook in a covered vessel.
2. Cook in an uncovered vessel.
3. Blanch, i.e., pour off the water after cooking 5 minutes, add 1 cup of
freshly boiled water, and finish cooking.
4. Cook in a steamer.
5. Cook in a steamer. Add 1 gram of ammonium carbonate per quart of
water to the water in the lower part of the steamer.
6. Cook in a pressure cooker.
7. Cook in a fireless cooker.
8. Cook in a waterless cooker.
9. Cook in a distilling flask, catching the distillate in a flask held in ice
water. Catch the distillate in 4 portions, changing the flask every 3 minutes.
Do not count the time for the first distillate caught in the flask until the water
in the distilling flask is boiling. Cork the flasks containing the distillate until
the class is ready to taste and smell the distillate. Which is stronger, the first
liquid that distils over or the last portion? Are any of the flavoring and aro-
matic substances of cabbage, turnips, and onions volatile?
Some of the distillate may be tested for sulfides by adding a few drops of
lead acetate. Test the distillate with litmus.
Taste the cooking water and vegetable. In which case is the flavor of the
vegetable best? Is blanching desirable? Do these experiments suggest any
reason why the juice of most canned vegetables is stronger than that from
the fresh vegetables? If you do not want to discard the water in which a
strong-flavored vegetable is cooked, how would you cook the vegetable? How
use the water? Test some of the cooking waters for sugar.
Vegetable used :
Time of
cooking
Tenderness
Flavor of
vegetable
Flavor of
water
Flavor of
distillate
Color of
water
FRUITS AND VEGETABLES
147
Conclusions.
B. Time of cooking.
Use Y^ pound (112 grams) of shredded cabbage for each experiment.
Should a difference be made in the time for winter and spring cabbage? Have
the water boiling when the cabbage is added. The amount of water will need
to be increased in each experiment as the time of cooking is increased.
1. Cook 5 to 7 minutes in a small quantity of water. Try to have nearly
all the water evaporated at the end of the cooking period.
2. Repeat Bl, but cook 8 to 10 minutes.
3. Repeat Bl, but cook 25 to 30 minutes. Add boiling water if necessary
to finish the cooking. Compare the flavor and color with those of the cabbage
cooked a shorter period.
4. To a cup of boiling milk add ^4 pound of finely shredded cabbage. Cook
5 to 7 minutes. Use a pan of at least a quart capacity, for milk boils over
readily. Compare flavor and color with Bl and B2.
5. Repeat B4, but cook 15 minutes.
C. The quantity of water left at the end of the cooking period.
1. Repeat the first two experiments under B, but have about Y% cup of
water left at the end of the cooking period. Drain and save cooking water.
How does the quantity of water compare with the measure of the vegetable?
Compare the flavor with that of vegetables from above experiments.
2. Repeat Cl, but have about ^4 cup of water left at the end of the cooking
period. Compare the flavor of the cooking waters.
3. Repeat B and C with Brussels sprouts, cauliflower, and white onions.
4. If the water you use is alkaline in reaction, repeat Cl or C2, using dis-
tilled water and cauliflower or white onions.
5. Cook l /4 pound of peas, asparagus, carrots, or other vegetables until
tender, (a) Have the water evaporated at end of cooking period, (b) Have
about Y% cup of water left, (c) Have about 24 cup of water left, (d) Cook
in 1 cup of milk.
Time of
cooking
Quantity of
water left
Texture
Color
Flavor
Results and conclusions.
What is the effect of long cooking on strong-flavored vegetables? Are some
vegetables often over-cooked? Is cabbage sometimes cooked longer than 25 to
30 minutes? Name several strong-flavored vegetables. Do cabbage and cauli-
flower turn a brownish red unless cooked too long? Do onions become stronger
in flavor with longer cooking? What length of time of cooking produces the
best-flavored product for onions, cauliflower, and the other vegetables used?
With which vegetables would you have considerable water left at the end
of the cooking period? Would the age of the vegetable, that is, young or old
carrots, turnips, etc., make any difference in the quantity of water that is
desirable to be left at the end of the cooking period? With which would you
148
FRUITS AND VEGETABLES
evaporate the water? Would you increase the water proportionately for a
larger quantity of vegetable? Do vegetables like cabbage and onions lose juice
during cooking that adds to the cooking liquid? What is the percentage of
water found in some common vegetables?
Is the flavor of the vegetables cooked in milk as strong as when cooked
in water? Do any of the vegetables curdle the milk? Which ones? (See chapter
on milk.)
What is the effect on the color of white vegetables of cooking in alkaline
water? In distilled water?
Experiment 20.
To determine the comparative losses in cooking vegetables by different
methods.
A. Use 300 grams of carrots cut into cubes of the same size. Mix well and
use 100 grams in each experiment. Use distilled water.
1. Cook until tender in a steamer. Save the water. Partially evaporate the
water in the cooking utensil. When it is sufficiently concentrated put into a
weighed evaporating dish. Rinse the cooking vessel with a small quantity of
distilled water and add to the evaporating dish. Evaporate to dryness. Weigh
the residue and determine the percentage of loss in the cooking water.
2. Cook in sufficiently boiling water to barely cover. Measure the quantity
of water used. Watch carefully. If the water evaporates before the vegetable
is tender add boiling water. Remove the carrots from the cooking vessel w r hen
they are tender and rinse the cooking vessel with a small amount of distilled
water. Put the water in a weighed evaporating dish. Evaporate to dryness
and weigh the residue.
3. Cook in 3 times the amount of boiling water used in A2, so that a rather
large amount of water is left when the carrots are done. Evaporate the water
according to directions under Al.
B. Use 3 medium-sized potatoes for each experiment. The potatoes should
be nearly the same size. Use distilled water.
1. Cook with skins on. Evaporate the cooking water after the potatoes are
removed until only a small quantity is left. Put in a weighed evaporating dish,
evaporate to dryness, and weigh the residue.
2. Peel the potatoes. Cook until tender. Proceed as in Bl. In which case
did the greatest loss occur with the carrots? With the potatoes?
Weight of residue
Al
A2
A3
Bl
B2
By what methods are the losses in cooking vegetables the greatest? How
can the losses be reduced to a minimum? What do you think of the advisa-
bility of throwing away the juices from canned vegetables? The water in
which vegetables are cooked ?
Results and conclusions.
FRUITS AND VEGETABLES
149
Experiment 21.
To determine the best method of cooking dried vegetables.
Use 50 grams of dried beans for each experiment. Keep a record of the
time required for cooking, the weight after soaking and after cooking. Start
the soaked beans to cook in 1 cup of boiling water and the unsoaked beans
in 1 pint. If the beans become dry before they are cooked add boiling water
of the same kind used in that particular experiment. Cook all the beans in
covered pans. Test the beans with the sharp point of a knife or fork. Compare
with your neighbors' results, to try to have all cooked to the same stage of
doneness. If you have water softener, to soften hard water, repeat the experi-
ments that call for tap water to compare with the results for hard water and
distilled water.
1. Wash the beans and soak over night in tap water. Discard the water in
which the beans were soaked. Weigh the beans. Add fresh tap water and cook
until tender. Drain and weigh.
2. Soak over night in tap water to which % teaspoon of soda is added.
Discard the soaking water and proceed as in 1.
3. Soak the beans over night in distilled water. Discard the soaking water
and weigh the beans. Add fresh distilled water and cook until tender. Drain and
weigh the beans.
4. Soak over night in distilled water to which % teaspoon of soda is added.
Discard the soaking water and weigh the beans. Proceed as in 3.
5. Cook in tap water without soaking. Weigh.
6. Cook in tap water to which l /% teaspoon of soda is added. Cook for 10
minutes, then discard the water and add fresh water. Cook until tender. Weigh.
7. Cook in distilled water until tender. Weigh.
8. Cook in tap water to which ^ teaspoon salt per 50 grams of beans has
been added. Weigh.
9. Cook in the pressure cooker for 30 minutes at 20 pounds pressure.
10. Cook in distilled water to which 1 tablespoon of vinegar is added.
11. Pour boiling water on the beans. Let stand. Weigh beans every hour to
compare the length of time required for soaking in warm and cold water.
Weight of beans
after soaking
grams
Weight after
cooking
grams
Time to
cook
Texture
Flavor
Results and conclusions.
Compare the time required for cooking by the different methods. In which
is the best product obtained? Do any of the beans tend to lose their shape?
Which beans cook in the shortest time? What is the effect of soaking on the
color and flavor of the beans? On the time required for cooking?
Experiment 22.
To determine the effect upon the texture of fruit of cooking in a sugar sirup.
A. Cooking in a sirup and adding the sugar after cooking.
150 FRUITS AND VEGETABLES
1. To 1 cup of water add a cup of sugar. Bring to a boil. Pare and core
6 apples. Do not cut in pieces. Cook in the sirup. The sirup should be in a
rather small pan so that the apples are covered by the boiling sirup. Cook
until the apples are translucent in appearance. It may be necessary to cook
only a portion of the apples at a time.
2. Peel and core 6 apples. Cut into quarters or eighths. For each \ l /2 pounds
of peeled apples add 1 cup of water and cook until soft. When soft add %
cup of sugar for each \ l /2 pounds of pared apples. Compare with the consistency
of the apples cooked under 1.
B. To determine the effect of length of time of cooking upon the flavor and
the proportion of sugar to fruit upon the texture of the fruit in strawberry
preserves.
1. Wash and stem strawberries. For each pound of fruit (approximately
1 quart) add 1 pound of sugar and let stand in the refrigerator over night.
When ready to cook place in a rather large sauce pan for the quantity of
berries, so that they can boil rapidly without danger of boiling over the top of
the pan. Heat slowly and shake the pan occasionally. When the temperature
reaches 65 to 70C. (150F.) remove the pan from the heat and keep warm
for about 5 minutes. Roll the berries occasionally in the sirup. Put over the
heat and bring to a boil quickly. Cook until the temperature of the sirup
registers 103C. Let stand until the bubbles cease to form. Pour in sterilized
containers. If the berries float to the top of the can repeat the experiment,
increasing the time the fruit is held in the sirup at a temperature of 65C. Let
stand a few days before making comparisons with other preserves. Keep a
record of the time required for cooking.
2. Repeat 1, but for each pound of fruit add \ l /2 pounds of sugar.
3. Repeat 1, but for each pound of fruit add 2 pounds of sugar.
4. To 1 pound of berries add 1 pound of sugar. Let stand over night in
refrigerator. Bring to boil and boil 5 minutes. Add another pound of sugar
and bring to boil. Boil 5 minutes, partially cool, can, and seal.
5. Repeat 4 but pour berries into a large platter and let stand until sirup
is the consistency desired. Seal in sterilized jar.
6. Repeat 4, but put berries in a sieve after stemming and pour boiling
water over them. Put in kettle, add sugar, and proceed as under 4.
7. Make a sirup of 1 pound of sugar and 1 cup of water. When it is boiling
add 1 pound of berries. Cook until the temperature of the sirup registers
103C. Store according to directions under 1.
C. To determine the effect of time of adding sugar in making preserves
upon the texture of a firm fruit like Keifer pears.
1. Pare and core Keifer pears. Cut into quarters or eighths. To each pound
of fruit add a pound of sugar and a cup of water. Cook until the sirup is the
concentration desired.
2. Repeat 1, but first cook the pears until tender in water. Then add a
pound of sugar for each pound of fruit and cook to the same concentration
as under 1.
Compare the consistency, texture, and flavor of the apples cooked in sirup
with those cooked in water and then sweetened. Which is preferable for an
apple that is to be served whole? For a puree? Would putting the cooked
FRUITS AND VEGETABLES 151
apples through a sieve aid in obtaining a uniform texture for apple sauce?
Are the apples used for the experiment a sweet or a sour variety?
What is the concentration of sugar in a sirup that boils at 103C.? See
Table 10 under sugar cookery. It is desirable for some preserves to have a
greater concentration of sugar in the finished preserves. If 65 per cent of
sugar is desired, to what temperature should the sirup be cooked? If a 70
per cent concentration is desired? What is the effect of longer cooking upon
the flavor of strawberry preserves? Is it preferable to add the sugar directly
to the berries or to make a sirup first? Why?
Compare with the preserves from B in flavor, color, texture, and yield.
In a fruit like Keifer pears, which contain considerable cellulose, what is
the best method of making preserves? What is the effect upon the texture of
adding the sugar directly to the fruit? Would you cook dried fruit in a sirup?
Why?
CHAPTER V
JELLY
The earliest work on jelly from a school laboratory is that of Gold-
thwaite. Since that time many valuable contributions have been made deal-
ing with jelly making. Probably the most extended recent investigations
are those of Spencer, of Olsen, and of Tarr and his associates, Baker and
Myers. They believe that the formation of jelly "depends almost entirely
upon the application of the laws of chemistry, more especially the laws of
physical chemistry."
Jelly formation. Spencer offers a new theory for gelation of pectin
jells. Stated briefly it is as follows. A pectin sol is stabilized by hydration
and a negative charge of the pectin particles. The greatest stability comes
in the neutral range as increasing either alkalinity or acidity decreases its
stability. In jelly the role of the sugar is that of a precipitating agent: the
more acid the solution, the less sugar required for the precipitation of the
pectin. Salts may aid in precipitation or tend to prevent it, depending on
whether they increase or decrease the stability of the pectin.
For theoretical study of pectin jelly Spencer recommends mixing the
constituents of the jelly while cold instead of the usual boiling of the
sugar and juice, which she calls the hot evaporation method. The reasons
for this are four in number. Decomposition of both sugar and pectin occurs
during cooking. The proportions of the various constituents change by
evaporation, hence it is difficult always to obtain the concentration desired.
The precipitating agent sugar has a limited solubility. There is danger
of premature precipitation of the pectin if all the cold sugar is added at
one time to the hot pectin mixture. For this experimental work dried pectin
or a concentrated pectin solution is necessary.
Olsen summarizes the theory of jelly formation as follows: Granted that
pectin is a negatively charged hydrophilic colloid, the following may be
assumed: (1) sugar is the dehydrating agent; (2) the hydrogen-ion con-
centration reduces the negative charge on the pectin, thereby permitting the
pectin to precipitate and coalesce in the form of a network of insoluble
fibers, provided the concentration of sugar is sufficient; (3) the dehydration
of the pectin micelles by sugar is not instantaneous but requires time to
come to an equilibrium; (4) the rate of hydration and precipitation in-
creases in direct ratio as the hydrogen-ion concentration; (5) the maximum
jelly strength is reached when the system reaches equilibrium, and depends
upon the position of that equilibrium; (6) any component added to a pectin
jelly system, including salts, which causes a change in the ultimate jelly
152
SOURCES OF PECTIN IN PLANTS 153
strength of that system may function either (a) by changing the rate of
gelation, or (b) by affecting the ultimate jelly structure, or (c) a com-
bination of these two.
Fruits Used for Jelly
For a fruit juice to make a good jelly by boiling with the addition of
sugar only, the juice must contain a sufficient amount of a substance called
pectin and also sufficient acid. Some fruit juices will not make acceptable
jelly by this method because they are deficient in pectin, whereas others
do not contain enough acid. In the middle states west of the Mississippi
River the fruits most commonly used to make jelly without addition of
pectin are apples, crab-apples, blackberries, sour plums, grapes, currants,
and gooseberries. During the winter months cranberries are used exten-
sively.
Cruess and McNair have reported that the following fruit juices con-
tain sufficient acid and pectin to produce good jelly: blackberries, logan-
berries, Isabella grapes, Tokay grapes, cranberries, currants, whole lemons,
and pomelos. They state that oranges have enough pectin but not always
enough acid. Apricots and cherries sometimes make jelly but are usually
deficient in pectin. Pomegranates and strawberries have enough acid but
lack pectin, and pears, peaches, and huckleberries lack both pectin and acid.
Citron melons and mission figs have enough pectin but lack acid. They state
that lemon is too high in acid to produce a good jelly, but that two whole
oranges and one whole lemon make a good combination, the acidity of the
lemon allowing for the deficiency in the orange.
By the addition of pectin and sugar, all fruit juices, so far as the author
knows, can be used for jelly.
The Pectic Substances
Nomenclature of the pectic substances. The different names used
in the literature for pectin and its related compounds have been numerous.
To avoid confusion, the Committee on the Nomenclature of the Pectic
Substances (Dore, Chairman) have proposed dividing these into three
groups: (1) protopectin, (2) pectin, and (3) pectic acid. The chemical
identity of the various pectic substances is not definitely settled, but a
great deal of investigational work is being done at the present time.
Function of pectic substances in plant life. The pectic substances
play an important role in plant life. Dore states that the primary function
of the pectic substances is the cementing together of the individual cells
that compose the plant.
Sources of pectin in plants. The pectic substances are found in the
leaves, bark, roots, tubers, stalks, and fruits of plants. The pectic com-
pounds occur in two places in the plant cell in the middle lamella, where
154 JELLY
they serve as cementing material, and as thickened places on the cell wall.
These two sources may yield slightly different substances. In fruits the
pectin is usually found in the pulp and not in the juice, though there are
some exceptions. For example, currant juice often contains pectin. The
skins and cores of fruit like apples contain large proportions of pectin.
Hence, apples and crab-apples are cut into small pieces, but not peeled
or cored, for making jelly. Some of the root stocks, such as sugar beets,
carrots, rutabagas, and turnips, contain appreciable amounts of pectin.
The amount of pectin not only varies in different fruits, but also in the
same fruit at various stages of ripeness and in the same fruit in different
years or seasons.
Protopectin. Protopectin has been called pectose and pectinogen. It
is the water-insoluble pectic substance in plants. It may be rendered soluble
by the enzyme protopectinase or by treatment with acid and other reagents.
The soluble substances thus formed are designated as pectins.
Sucharipa has presented evidence that the protopectin is combined with
cellulose. In the plant, the separation of the pectin from the cellulose is
brought about by hydrolysis by the enzyme protopectinase.
The protopectin is the precursor of pectin. As the fruit ripens, pectin
increases while the protopectin decreases. Protopectin is also converted to
pectin by boiling with dilute acid. Since fruit juices contain acid, some
protopectin is changed to pectin when the fruit is boiled. This is the reason
why cooked fruit juices are better for jelly than uncooked ones.
Conrad', influenced by Ehrlich's work, found that as the pectin of the
fruit increases, a pentose-bearing polysaccharide is liberated at the same
time from the protopectin, its proportions paralleling that of the pectin
to a great extent. This furfural-yielding polysaccharide is separated from
the pectic substances by its solubility in 70 per cent alcohol.
Pectin. Among the various names that have been applied to pectin are
parapectin, pectinogen, and protopectin. The term is applied to the meth-
ylated pectic substances that form a colloidal solution in water. It is the
jelly-forming substances of the pectic compounds, although the pectins with
fewer methyl groups have less jellying power than those with a greater
number.
According to Sucharipa the pectins may be classified into ( 1 ) free pectins,
which are removable from the plant by water solution, and (2) hydrol-
ysis pectins, which result from treating protopectin with hydrolyzing
agents.
Pectic acid. In fruit, protopectin is changed to pectin by enzymes of
the fruit. With still further ripening, pectic acid is formed from pectin
by the enzyme pectase. These changes are gradual, but the larger portion
of the pectic acid is formed when the fruit is ripe and when decay begins.
In the presence of pectase and calcium, barium, or strontium salts, pectic
acid may form a gel.
Dore states that, when the protopectin is in combination with cellulose,
THE PECTIC SUBSTANCES 155
the under-ripe fruit is firm. As the fruit ripens it becomes softer as the
protopectin is changed to the pectin. Rotten fruit is entirely disintegrated
because the pectin has been changed to pectic acid.
In fruits the rate at which softening takes place depends largely upon
the temperature. Haller has shown this for a number of varieties of apples
in storage. The rate "at 40 F. was found to be slightly more than double
that at 32, whereas that at 50 was slightly less than double that at
40, and that at 60 nearly double the rate at 50."
Pectinase is a term applied to the enzyme which hydrolyzes pectin and
pectic acid into their simplest cleavage products.
Constitution of the pectic substances. The constitution of the
pectic substances is not definitely known. The purest pectins, when treated
with a dilute alkali, yield 10 to 12 per cent of methyl alcohol, showing
that methoxy groups (CH 3 O) are found in the molecule. As the methoxy
groups are split off, different series of pectin compounds are formed, these
compounds having different jellying powers. The greater the number of
methoxy groups split off, the less the jellying power and the more sirupy
the jelly. Pectic acid is the demethoxylated pectin. Since pectic acid is the
simplest and the most easily purified of the pectic compounds, it has been
prepared in the purest state. Schryver and Haynes have suggested that
pectic acid is composed of one molecule of galactose, one of arabinose, and
four of galacturonic acid arranged in a ring, the last having the four car-
boxyls of the acid groups free for methyl ester formation.
Sucharipa states that the chemical difference between free pectins and
hydrolysis pectins is that arabinose is in the former, whereas it is split off
from the latter by hydrolysis.
Other investigators question the presence of arabinose as a constituent
of pectic acid, since it is impossible for it to be formed from galacturonic
acid. Acetic acid has been reported among the decomposition products of
pectic acid obtained from pectin of flax and sugar beets.
Olsen states that most of the recent work on the chemistry of the pectin
molecule fails to consider that pectins may vary depending upon their source.
He adds that it has long been known commercially that citrus and apple
pectins, irrespective of grade, form jellies of definitely different types,
though this has not been recognized in the scientific literature.
Protopectin and pectic acid do not form jellies. Protopectin and
pectic acid do not form jelly when cooked with sugar and a fruit juice
containing acid, although pectin forms a jelly under these conditions. Since
over-ripe fruit contains a larger proportion of pectic acid and a smaller
percentage of pectin, this furnishes the explanation for the fact that many
jelly makers have long known, that juice from partially ripe fruit makes
a better jelly than juice from over-ripe fruit.
Cooked extracted fruit juice is better for jelly. Fruit juice ex-
tracted raw or without cooking will seldom make jelly, or it yields a jelly of
poor quality. Since the protopectin is not soluble in the juice of the fruit, if
156 JELLY
the juice is extracted raw it remains with the pulp of the fruit. If cooked,
some of the protopectin is changed to pectin. Goldthwaite has reported
experiments with apple and some other fruit juices extracted raw. Either
no jelly was obtained or it had a poor texture.
Extraction of and preparation of juice for jelly. Hard fruits like
apples and crab-apples are cut into small pieces or ground with a food chop-
per, barely covered with water, and cooked. Soft berries need little water
added, j4 CU P to a pound of fruit often being used. Currants that are not
too ripe should have a larger proportion of w r ater. Gooseberries, if green,
because of their very high acid and pectin content and the character of the
pectin, can be completely covered with water, and sometimes will need
additional w r ater. Ripe gooseberries require the same proportion of water
used for other berries. After cooking, the juice is drained without squeezing
from the pulp by placing the cooked material in a cloth bag. Fruits that
are very rich in pectin may have two or three extractions made. These
second and third extractions need to be boiled down more than the first
extraction to concentrate the pectin. Second and third extractions also do
not have as much of the fruit flavor as the first one.
Apple juice sometimes contains starch, particularly that from under-ripe
fruit, which renders the juice cloudy. Askew states that starch formation
begins near the periphery and progresses toward the core ; but as the fruit
matures the core area is cleared of starch first, the area near the skin last.
Commercially, diastase can be added to convert the starch to sugar and thus
clear the juice.
Grape juice contains tartaric acid, which often crystallizes in long needle-
like crystals in the jelly. It can be removed partially from the juice by put-
ting the juice in a refrigerator (the colder the better, but it is less soluble
at lower temperatures), over night, or for a few days, and then straining
the crystals from the juice.
The Role of Pectin in Jelly Formation
According to Spencer's theory, the precipitation of pectin forms the jelly.
Sugar, glycerin, or alcohol may be used as precipitating agents. Spencer
states "The successful making of alcohol jellies requires rapidity of motion
and practice, otherwise one obtains a precipitate and not a homogeneous
jelly." The qualitative aspects of the boundary line between fields of the
jelly and the sol shown in Fig. 14 are by Spencer. She states that the
quantitative aspects of these boundary lines are meaningless, because the
pectin used contained some ash. From this figure it is deduced that jellies
with sugar as the precipitating agent are not possible in the neutral region
owing to the solubility limit of sugar. Although alkaline jellies are in-
teresting theoretically, practically they are of less importance, since they
cannot be used as food on account of their flavor.
Concentration of pectin required for jelly. The strength of the
PECTIN TEST BY ALCOHOL
157
jelly is in proportion to the concentration of the pectin, if other factors re-
main the same. Too small a proportion of pectin yields a jelly that is too soft
and sirupy ; too great a concentration gives a product that is too firm and hard.
However, after a certain amount of pectin has been added any excess re-
mains inactive. The concentration of pectin required for a jelly of good con-
sistency varies with the proportion of sugar used, the acidity of the juice or
solution, the salt content of the particular juice being used, the time, and
temperature factors. Good home-made jelly may contain 0.75 to 1.0 per
cent of pectin. Commercial jelly, on account of shipping, is somewhat stiffer,
averaging about 1.25 per cent of pectin.
Pectins from different sources yield characteristic jellies. Olsen
states that jellies made from citrus pectins are comparatively friable and
Crystallization Limit
Alkaline
Neutral
Acid
X-Axis; % Precipitating Agent
FIG. 14. From Spencer. "A qualitative view of the relations of the boundary
curves of pectin jelly fields for sugar, glycerine, and alcohol jellies. The alcohol
jelly field is the largest, and the sugar jelly field the smallest." J. Physical Chem.
33: 1993.
have little elasticity; whereas jellies made from apple pectins are highly
elastic, but require and tolerate less acid than citrus pectin jellies similarly
prepared. Cranberry pectin tends to yield firm jellies which will not spread
readily. Cox states that a better-textured cranberry jelly for spreading pur-
poses is obtained if the pectin occurring in the juice is hydrolyzed by adding
the enzyme pectinase, available in commercial form under the name Pec-
tinol. A slower-setting pectin is then added to the juice. With a rapid-
setting pectin gelation may start before the sirup is poured, and the pouring
breaks the structure so that a mass of small lumps is formed.
Three fairly easy methods of determining the amount of pectin present
in fruit juice are available for the housekeeper. One is to cook a small
portion of the juice with sugar to see if it will form jelly. Another is to
test the juice with alcohol. The third is to test the viscosity of the juice
with a jelmeter.
Pectin test by alcohol. Alcohol precipitates pectin in a jelly-like mass.
By the character of the precipitated pectin an approximate estimate can be
made of the amount of pectin in the juice. For the test, 1 tablespoon ol
158 JELLY
juice is poured into 3 to 5 tablespoons of alcohol. Sometimes equal quantities
of juice and alcohol are used, but the larger amount of alcohol gives a
better test. Turn the container gently from side to side. If a test tube or
graduated cylinder is used it can be turned slowly upside down and back
to bring all the juice in contact with the alcohol. If the pectin comes down
in a solid mass there is a sufficient quantity to make jelly. If the pectin is
flocculent or in small flakes the juice needs boiling down to concentrate the
pectin.
Johnston and Denton have reported that the amount of alcohol precipi-
tate in citrus pectin extracts does not indicate the jellying power. It may
also be possible that the amount precipitated in different juices will show
different jellying strengths,. Of course, alcohol precipitates such substances
as gums and starch in addition to the pectin. The precipitated mass becomes
firmer after standing in the alcohol a few minutes, so the estimate should
be made just after mixing.
For the pectin test, straight ethyl alcohol, denatured, or wood alcohol
can be used. The denatured alcohol is better to use than the wood alcohol
and usually gives a satisfactory test. When wood alcohol is used, the
precipitated pectin may be redissolved after standing a few minutes. This
may also be true of some denatured alcohol.
Pectin test by viscosity. Based on the observed correlation of the
viscosity of pectin solutions with the jellying power of the pectin, Baker
has developed a jelmeter. The viscosity of the fruit juice is determined
by the rate of flow of the juice through a given orifice compared with the
time of flow of an equal quantity of water at the same temperature. The
viscosity or thickness of the fruit juice is dependent principally upon its
pectin concentration, although sugars, starches, and proteins influence it
slightly. If the approximate viscosity is known, then the amount of sugar
to use and the weight to which the jelly should be cooked can be determined.
Baker has prepared such tables.
The jelmeter is similar to a graduated pipette. The test is easy to make
and practical. It works satisfactorily with the fruit juices that have been
tested.
Effect of high temperatures and a long period of heating upon
pectin. Numerous investigators, among them Johnston and Denton,
Sucharipa, and Tarr, have found that high temperatures decrease the jelly-
ing power of pectin. Myers and Baker state that "Prolonged heating of
pectin solution has a deleterious effect on the jellying power of the solution.
The higher the temperature the greater the decrease in jellying power
of the pectin." They find that heat has the same effect on the powdered
pectin as upon the pectin in solution.
The boiling of a pectin solution with acid decreases the amount of pectin
in the solution because of the formation of pectic acid by hydrolysis. Some
of Tarr's data seem to indicate that, if the sugar is in the juice during
COMMERCIAL PECTIN
159
the boiling period, hydrolysis is delayed. The following table is from
Tarr's results and shows that the decrease in jelly strength was con-
siderable when the pectin and acid were boiled before the sugar was added.
Commercial pectin. Commercial pectin is on the market in two
forms : ( 1 ) the liquid form and (2) the powdered dry pectin. The first type
of commercial pectin is a concentrated liquid pectin. It usually contains 4
to 4.5 per cent of pectin. The second form is a mixture of dry powdered
pectin and sugar. It is similar to dry gelatin and sugar mixtures on the
market in that it contains the sugar, and only the juice needs to be added
for making jelly. Wilson states that there is no uniformity in jelly strength
TABLE 21
THE EFFECT ON JELLY STRENGTH OF BOILING THE PECTIN WITH ACID PREVIOUS
To ADDING THE SUGAR (Tarr)
Time of boiling
pectin and acid,
minutes
Time of boiling
pectin, acid and
sugar, minutes
Jelly strength, pressure
in centimeters of water
Top
Bottom
0.0
19.4
61.5
79.5
1.0
19.2
58.0
77.5
2.0
19.5
58.5
76.5
3.0
17.2
57.5
73.0
4.0
17.5
55.5
70.5
6.0
13.2
49.5
67.5
8.0
11.0
44.0
62.0
10.0
9.0
41.0
58.5
11.3
6.3
39.5
54.5
12.0
6.3
33.5
49.0
of these pectin preparations but that a dry pectin that will jell about 40
times its weight of sugar is a practical one. The dry powdered pectin is
sold in large quantities to commercial jelly and jam makers. The dry pectin
without the added sugar is now available for the housekeeper.
Rooker states that the powdered pectins will eventually replace the
liquid pectins. This is because the "powder is cheaper, is easier to handle,
haul, cart, and store. It does not spoil and deteriorate. Powdered apple
pectin retains its jellying strength indefinitely while sirup pectins deteriorate
if kept any material length of time. A container of powdered pectin may
be opened and used as needed, while a container of pectin sirup must be
used almost at once or the balance of the opened can will spoil."
Rooker gives many uses of pectin in addition to making jelly and jam.
Among these are use in emulsions for pharmaceutical purposes, in emul-
160 JELLY
sions for tree spraying, in crushed fruits for soda fountains, as "candy
doctors," in confections, etc.
Myers and Baker after extensive experiments with the jellying proper-
ties of pectic substances, recommend that pectin should be bought and sold
on a basis of jellying strength.
Olsen states that, commercially, pectins are graded on the basis of the
amount of sugar they will carry. Thus a 160-grade pectin, as supplied by
a definite source, is one which, when used in a jelly containing 65 per cent
of sugar by weight w r ith a proper amount of acid in the proportion of one
part of pectin to 160 parts of sugar, yields a satisfactory jelly. Olsen has
also shown that the strength of a jelly will vary with the temperature to
which the pectin is heated. Hence a standardized procedure for testing
pectin strength is essential.
With the aid of commercial pectin, which the housekeeper can add to
fruit juices that are deficient in pectin, jelly and jam can be made from
many varieties of fruit.
The Role of Acid in Jelly Formation
Although acid is not essential for jelly formation its presence in fruit
jellies is very important. Singh has reported that "between certain limits
the greater the acidity of the juice the lower the amount of sugar re-
quired." He adds that it has long been known that juices of high acidity
yield firmer jellies than juices deficient in acid but with as high a pectin
content.
Spencer has published data showing the increase of rigidity of jellies
with increase of acid when the pectin and sugar concentrations are con-
stant. Spencer explains the action of acid in this way. The strength of a
jell network depends upon the continuity and the rigidity of the structure.
"Continuity of structure, by hypothesis, depends upon the number and
proximity of pectin particles at the time of precipitation," \vhich in turn
is determined by the degree of dispersion and concentration of the pectin.
"Differences in rigidity are due to the amount of water retained by the
pectin at the equilibrium established during precipitation." Hydrogen (or
hydroxyl) ions lessen the stability of the pectin sol by decreasing the hydra-
tion capacity of the pectin. Hence in an acid medium less sugar is required
to bring about precipitation. Nearly neutral fruit juices will not form
jelly with sugar because the sugar is not soluble enough to allow precipita-
tion of the more stabile pectin. Hence with a definite concentration of
pectin the rigidity of the jelly is determined by the sugar and acid con-
centrations.
Hydrogen-ion concentration and jelly. Tarr has determined the
minimum amounts of several acids required to produce a jelly and also
the amount of the acids to produce an optimum jelly by the hot evaporation
method with pectin, sugar, acid, and water. Optimum jelly is defined as
ACIDS IN FRUITS 161
the jelly which in his judgment has the best texture. For jelly formation,
when other conditions were standardized, the minimum amounts of the
acids were as follows: 8.5 cc. of 0.1 N sulfuric acid; 27.5 cc. of 0.1 N
phosphoric acid; 22.7 cc. of 0.1 N tartaric acid; 52.9 cc. of 0.1 N citric
acid; and 583.3 cc. of 0.1 N acetic acid. The total acidity of the minimum
amounts required for forming a jelly varied, but the acids were all at the
same />H, 3.40. For optimum jelly the acids were all at />H 3.1.
But although hydrogen-ion concentration controls the formation and
character of the jelly to a certain extent, the salt content of pectin or of
fruit juices, the temperature to which the pectin is heated, and the rate of
pouring may extend this />H range, as will be seen later. In Tarr's jelly a
pH of 3.46 gave a very tender jelly, but increasing the hydrogen-ion con-
centration below pH 3.1 gave syneresis or weeping. The best jellies were
obtained with pH 3.3 to 3.1. Olsen and others have suggested that with pH
lower than 3.1, jelly failure and increased syneresis may result because of
the increased rate of setting. Olsen has shown that an increase of hydrogen-
ion concentration increases the rate at which the jelly sets.
The hydrogen-ion concentration of ordinary fruit juices depends upon
the particular acid present, upon the quantity of acid present, and upon
the "buffer" action exerted by the particular juice.
Relation of the time factor to optimum acidity. Olsen assumed
that the lowering of jelly strength might be caused by incomplete dehydra-
tion of the pectin and lessened precipitation or by a more flexible network
of pectin. To test the second postulate he prepared jellies by heating the
pectin to 55C. and to boiling. The jelly at 55 was made as follows: The
pectin, 30 grams of sugar, and water to make a total weight of 140 grams
were brought to 36C. The minimum amount of acid, the remaining sugar,
and water were boiled together, cooled to 65 C., and adjusted to correct
weight with distilled water. The additional acid and the pectin solution
were added and stirred, the time was varied from the moment the pectin
solution was poured into the warm sirup until the mixture was poured in
jelly glasses, as shown in Table 22. The strength was tested with a Tarr
and Baker jelly strength tester. Olsen states that a high-grade pectin made
by the standardized hot method gives a reading close to 45.
The optimum pH varies with the time factor. The principal variation is
the rate of gelation of the pectin as influenced by the acid concentration.
Olsen explains this as follows: "The largest or 'optimum' amount of the
acid to be used will be that point at which an additional increase in acid
will increase the rate of setting to a point where loss in jelly strength due to
a disturbance of the jelly in the stirring or pouring exactly balances the
strengthening effect of that same increment of acid." Or in other words,
stirring or pouring hinders jelly formation, which is offset by increasing,
the hydrogen-ion concentration.
Acids in fruits. The acids occurring naturally in fruit juices that
are used for jelly are tartaric, malic, and citric. Sometimes acetic acid is
162
JELLY
TABLE 22
THE RELATION OF THE TIME FACTOR TO OPTIMUM ACIDITY. (Olsen)
(The time indicated is the interval between the pouring of the pectin solution
into the sugar sirup and the pouring of the mixture into glasses. Jellies contain
60 per cent of sugar, 2.5 grams of apple pectin 119F., phosphoric acid as in-
dicated. Temperature of pectin solution 36C.; of sugar solution 65C.; of final
mixture 55C.) (Olsen}
Series B
Series C
Series D
25% phos-
phoric acid
solution
90 seconds
50 seconds
8 seconds
cc.
Jelly
strength
pH
Jelly
strength
pR
Jelly
strength
pH
0.26
0.0
3.27
0.36
33.0
3.10
36.5
3.13
0.56
69.0
2.80
67.0
2.88
0.86
80.0
2.50
0.96
41.0
2.39
....
....
115.0
2.40
1.06
....
75.0
2.37
1.26
61.5
2.24
1.56
19.0
2.13
120.0
2.13
1.96
14.5
2.03
28.5
2.00
145.0
2.01
3.96
135.0
1.76
added to apple juice to make spiced apple jelly. Tarr's results show that
acetic acid is of little value to add to a juice to increase its jellying power,
because it volatilizes during boiling and is only slightly ionized in solution.
Goldthwaite has reported that, when tartaric and citric acids were used to
acidify fruit juices deficient in acid, tartaric acid gave better results, the
texture and flavor being better than when citric acid was used. Tarr's
results confirm Goldthwaite's observations. Spencer explains this difference
in the following manner. Since pectin sols are partially stabilized by a
negative charge, the preferential absorption of one anion above that of
another would increase the stability of the pectin sol. In other words, the
citrate ion is more strongly absorbed than the tartrate ion, hence increases
the negative charge on the pectin to a greater extent, making it more stable,
less easily precipitated, so that a weaker jelly is obtained with citric acid
than tartaric, if the same concentrations of pectin and sugar are used.
Methods of reporting acidity of fruit juices. Investigators have
reported concentration of acids required for jelly in different ways. The
/>H gives the concentration of hydrogen ion or ionized part of the acid.
Some report acid as number of cubic centimeters per 100 grams of jelly.
However, work done some time ago was usually reported in percentage of
ROLE OF SALTS IN JELLY FORMATION 163
some acid, not necessarily the one found in the fruit. It has often been
reported as sulfuric acid. The concentration of the acid is determined by
titration with an alkali ; from the quantity of alkali required the percentage
of acid is calculated. Campbell states that 0.3 per cent as sulfuric acid
is required to produce a jelly of good quality, the minimum being 0.27
and the maximum 0.5 per cent. Goldthwaite has reported from 0.154 to
1.892 per cent as sulfuric acid. Singh has reported still lower percentages
of acids than these, but his jellies with a very low percentage of acid
contain an unusually high percentage of pectin.
The Effect of Temperature to Which Pectin Is Heated
on Jelly Strength
Olsen states that the abnormally high jelly strength with pectin heated
to only 55, shown in Table 22, is not the result of the time factor alone.
To prove this he recovered the pectin from duplicate batches of jelly, one
of which had been heated to 100 and poured; the other poured at 50C.
The recovered pectins were remade into jelly at 50. Both gave jellies test-
ing as high in strength as the original jelly poured at 50 C. This proved
that the lesser strength of the pectin heated to 100 was not due to hydrol-
ysis of the pectin but the effect of temperature upon the gel structure. From
these results Olsen concludes that "the structure of jelly is fundamentally
different when slowly set from the hot solution than when rapidly set from
the cool sirup. If we assume that pectin exists in two states of hydration;
that is, if the amount of water bound by the pectin fibrils differs depending
upon the temperature at which the pectin is precipitated, then a ready ex-
planation is at hand."
These results are not to be interpreted as showing that hydrolysis of the
pectin does not occur with long boiling but that none takes place with a
short-boil process.
The Role of Salts in Jelly Formation
The role salts play in jelly formation is not emphasized as much as
that of pectin, acid, and sugar, but it is an important one. All fruit juices
contain salts of the acids found in the fruit. In addition to these, other
salts may be found.
Halliday and Bailey have reported that the addition of calcium chloride
favors jelly formation, as somewhat lower concentrations of pectin, acid,
and sugar are required when it is added. On the acid side, sodium chloride
tends to prevent jelly formation, i.e., larger quantities of acid and sugar
are required when sodium chloride is added. Spencer has reported that on
the alkaline side sodium chloride tends to precipitate the pectin. Spencer
has also reported that, with the same anion, chlorine, the precipitating effect
of the cation increased with increasing valence, or Al > Ca > Na. With
164 JELLY
the same cation but different anions Spencer gives the order of absorption
of the negative ion by pectin as acetate > citrate > tartrate. This means
that the tartrate is not so strongly adsorbed as the citrate or acetate ions,
hence has less stabilizing effect and is more easily precipitated by sugar.
The chloride anion is more strongly absorbed than the nitrate or sulfate
ions.
Salts buffer a fruit juice so that more acid is required to give a definite
/>H when salts are present. But the hydrogen ion is not the only positive
ion in the fruit juice. Myers and Baker have found that the cation of the
salt may supplement the hydrogen ion, but only at definite hydrogen-ion
concentrations. No jelly was formed with added salts above />H 3.6. Thus
jellies from fruit juices may have a slightly wider range of hydrogen-ion
concentration for jelly formation than those from pure water, acid, pectin,
and sugar. Myers and Baker used sulfuric, tartaric, and citric acids and
the sodium salts of these acids in their investigations.
The negatively charged ion of a salt tends to stabilize pectin sols, but
those anions absorbed most strongly exert the most stabilizing effect. These
negatively charged anions may be neutralized by the positively charged ion
of a salt, but the adsorption of cations also varies, so that some have a
greater destabilizing effect than others. Since all pectins contain salts, the
quantitative recipes worked out for one pectin may not give exactly the
same results with other pectins because of a different salt content.
The Role of Sugar in Jelly Formation
Sugar, if its concentration and that of acid and pectin is sufficient, pre-
cipitates the pectin. Spencer explains this precipitation as follows. When a
pectin sol is formed, "an equilibrium is reached between the partial pressure
of the adsorbed water" of the pectin "and that in the dispersing medium."
When sugar is added to the pectin sol, this equilibrium is disturbed, for
when the sugar dissolves in the dispersion medium it lowers the vapor
pressure of the dispersing medium. As a result the pectin particles lose
water and are less stable. Increases in sugar accelerate the setting of the
jelly, probably because of increased dehydration, although rate of setting
is also modified by other factors.
Jelly without added sugar. Jelly can be made by boiling down some
fruit juices until they yield a "jelly test." The concentration of 2 cups of
gooseberry juice yields less than J /s cup of gummy, tough, sticky jelly. If
left with the lid off for a few days it becomes dry enough to handle. It
is very dark in color, looking and feeling very much like licorice candy.
The fruit flavor is present, although scarcely noticeable at first, because of
the extremely acid taste.
When to add sugar in jelly making. As previously stated, Tarr
has found that the jellying strength of the pectin is lessened if boiled
before the addition of sugar. Yet, if the sugar is added to the pectin and
PROPORTION OF SUGAR AND JELLY YIELD 165
acid prior to boiling, the jelly strength is not decreased even when boiled
as long as 42.8 minutes. Directions for making jelly often state to boil
the juice for a certain number of minutes before the sugar is added. From
Tarr's results it would seem a much better practise to add the sugar to
the juice and concentrate it after the sugar is added. Long boiling of the
sugar and fruit juice produces a darker-colored jelly, the extent of the
darkening depending upon the juice and the length of time of boiling. With
dark fruit juices this is not desirable, but it may improve the appearance
of light-colored ones. To prevent darkening after the sugar is added, the
jelly can be made in small lots so that boiling to the desired concentration
can be accomplished quickly. In extracting the fruit juice too much water
should not be added, as a large quantity of water only dilutes the pectin,
and then boiling is required to concentrate it.
Concentration of sugar in finished jell. Jelly can be made with a
wide range or proportion of sugar to juice, from about 40 to 70 per cent
in the finished jell. From the reports in the literature, the average per-
centage of sugar in commercial jelly, unless acidity or pectin is abnormally
high, varies from 60 to 65 per cent. The concentration of sugar desirable
in the finished jelly varies somewhat with the juice from which the jelly
is made. Thus gooseberry juice, which usually has a pH 2.6 to 2.8 and also
has a high pectin content, is usually of better texture if the final concen-
tration of sugar is short of or about 60 per cent. Cox states that for cran-
berry sauce too stiff a jelly can be prevented by stopping the boiling process
when the sugar concentration is somewhat below 60 per cent. Cox states
that premature gelation can be brought about by too much pectin, acid, or
sugar, or all three. For some fruit juices Tarr and Baker have found
that 70 per cent of sugar in the finished product gives a jelly of good tex-
ture. With higher concentrations than 75 per cent the sugar may crystallize
from the jelly.
Proportion of sugar and jelly yield in illustrations. In general,
other factors remaining constant, the yield of jelly parallels the amount of
sugar added. The gooseberry juice for the jellies in the illustrations is from
the same source, so that the pectin content and viscosity of the juice were
the same. The percentage of sugar in the finished jell is about 60, since all
were boiled to 103C. In Experiment 24 the yield of 'jelly parallels the
sugar added. See Figs. 15 and 16. The firmness of the different jellies
varies. The 2 cups of juice boiled down yield less than l /& cup of jelly. It
is very firm, hard, and difficult to pull apart. The percentage of sugar in
it is not known, but both the pectin and acid have been enormously concen-
trated. With l /\. cup of sugar to a cup of juice the yield is a little more
than y\ cup of jelly. This jelly is very firm, solid, and hard. With ^2 cup
of sugar to a cup of juice the yield is a little more than ^2 cup of jelly.
This jelly is a little more tender than the one with *4 cup of sugar but
produces a jelly that is still too firm. It should be remembered that whereas
each cup of juice had the same concentration of acid and pectin before the
166
JELLY
sugar was added, the addition of varying amounts of sugar and boiling to
103C. gives a concentration of practically 60 per cent of sugar in all the
jellies. But the boiling to produce a concentration of 60 per cent of sugar
thereby concentrates the pectin and acid, the concentration being greater
per unit of weight in the jelly to which the smallest proportion of sugar
was added. That the acid is concentrated is shown bv the flavor, for the
*Si$ ; ; ri Blte: yBHL.
WHB HHP
FIG. 15. The yield of jelly obtained when the proportion of sugar to juice is
varied. Experiment 24.
1. Jelly made from two cups of juice without added sugar.
2. A cup of juice and *4 CU P of sugar.
3. A cup of juice and ^> cup of sugar.
4. A cup of juice and % CU P f sugar.
5. A cup of juice and 1 cup of sugar.
6. A cup of juice and 1% cups of sugar.
7. A cup of juice and \ l / 2 cups of sugar.
jelly from Y\ cup of sugar and 1 cup of juice is very tart, the tartness
progressively decreasing as larger proportions of sugar are added. This is
true of the first extraction of most fruit juices. As the proportion of sugar
is increased, the yield of jelly is increased. There is a proportion of sugar
that produces the best jelly for the particular juice used. With increasing
amounts of sugar beyond the proportion that yields an optimum jelly, the
FIG. 16. Showing consistency and yield of jelly from Fig. 15. Jelly made from
first extraction of gooseberry juice.
jelly becomes softer until a proportion of sugar is finally reached that
results in a fluid sirup instead of a jell.
Proportion of sugar for home-made jell. The proportion of sugar
to add to the juice cannot be given definitely for the best texture of
jelly, since it varies with the pectin, acid, and salt content of the juice. The
amount of pectin varies with the ripeness of the fruit, the quantity of
SUGAR, PECTIN, ACID, AND SALT 167
water added for extracting the juice, and with the kind of fruit. Gold-
thwaite states that it is better to use too little sugar than too much with
fruit juices. She has found with all kinds of fruit juices and average
methods of extraction that % cup of sugar to a cup of fruit juice usually
gives better results than a cup of sugar to a cup of juice. The author's
laboratory and home results agree with those of Goldthwaite that 24
cup of sugar to a cup of juice gives a better jelly for most fruit juices.
Currants if not very ripe need a cup of sugar to a cup of juice, but if a
larger quantity of water is added for extraction a smaller proportion of
sugar is needed. The pectin content of gooseberry juice is usually quite
high, one reason being that they are nearly always picked while green. If
the rule of adding water to barely cover is used, the gooseberry juice will
often require \ l / cups of sugar to a cup of juice to give jelly of the best
texture.
FIG. 17. The jelly from the second extraction of gooseberry juice is softer than
the jelly from the first extraction with corresponding amounts of sugar.
1. A cup of juice and y\ cup of sugar.
2. A cup of juice and ^2 cup of sugar.
3. A cup of juice and ^4 cup of sugar.
4. A cup of juice and 1 cup of sugar.
5. A cup of juice and 1^4 cups of sugar.
Some idea of the amount of sugar to use can be obtained from the
alcohol test. With gooseberry juice and using the larger quantity of
alcohol for the test, the approximate proportion of sugar required for a
cup of juice can be estimated from the character of the precipitated pectin.
After mixing, turn the pectin and alcohol out in a dish. If the pectin
precipitate can be picked up in one piece without breaking and feels firm,
about 1^4 to 1 1/3 cups of sugar will be required; if the pectin precipitate
can be picked up in one piece without breaking but does not feel firm,
about 1 to \y% cups of sugar will be necessary; but if the precipitate breaks
into two pieces when picked up, about 24 to. % cup of sugar is required.
If the precipitate is flocculent the juice needs concentrating or only ^ cup
or less of sugar can be used. A still easier way to determine the best pro-
portion of sugar to add is to determine the viscosity with a jellmeter.
Sugar, pectin, acid, and salt. As can be ascertained from the previous
discussion there is a relation between proportion of pectin, sugar, acid,
and salts, temperature to which the pectin is heated, and time of pouring.
Increases and decreases of constituents may be made within certain limits.
Salts in the fruit juice or added to it may aid jelly formation or hinder
168
JELLY
and delay it, according to whether they tend to precipitate or stabilize the
pectin.
Inversion of sugar in jelly making. The saturation point of a
sucrose solution at room temperature or 20C. is 67 per cent. Thus
jellies containing more than 67 per cent of sucrose at 20C. are super-
saturated, unless something has occurred to the sugar. The pectin tends to
keep the sugar from crystallizing from solution, acting as a protective
colloid. But even this protective action would not always be great enough
to keep the sugar from crystallizing with a concentration of sugar that
is increased to 70 per cent or over. When sucrose is heated with acid, some
of the sucrose is inverted to dextrose and levulose. The amount of inverted
sugar formed during jelly making depends upon the acidity of the fruit
juice and the length of time of boiling with the sugar. Since there are
three sugars in the finished jelly the percentage or total sugar that can be
held in the finished jelly without crystallization occurring is increased.
Tarr and Baker report that in a solution containing a mixture of sucrose,
dextrose, and levulose, the total maximum solubility is obtained with the
proportions of each sugar shown in Table 23 (obtained from Bureau of
Standards).
At 20C. if inversion has occurred to obtain maximum solubility, about
75.7 per cent of sugar is soluble. Thus jelly containing about 70 per cent
of sugar is not necessarily supersaturated. The salts and organic con-
stituents of the fruit juice may also increase the solubility of the sugar
in a given solution.
Rate of inversion in different fruit juices. Tarr and Baker have
determined the rate of inversion of sucrose during jelly making with
equivalent solutions of sulfuric, tartaric, and citric acids. As would be
TABLE 23
TOTAL MAXIMUM SOLUBILITY WITH CANE SUGAR AND INVERT SUGAR
(Tarr and Baker]
Temperature,
C.
Grams of cane sugar
per 100 grams
solution
Grams of invert
sugar per 100
grams solution
Grams of water
per 100 grams
solution
20
37.1
38.6
24.3
25
35.7
41.4
22.9
30
33.4
45.6
21.0
expected, they found the inversion was greater with the stronger or more
highly ionized acid. Longer heating with a given hydrogen-ion concen-
tration also increased the amount of inversion.
Tolman, Munson, and Biorelow in 1901 obtained results, which we are
DEXTROSE 169
now able to interpret on the basis of our present knowledge, on the inver-
sion of sucrose by juices of different fruits. Their work was published
before hydrogen-ion concentration was thought of in connection with jelly
making. After determining the amount of invert sugar in a series of jellies
and jams that they had made, they concluded that the inversion of the
sucrose varies with the total amount of free organic acid present and the
length of time the product is heated. But they found some exceptions to
their conclusions. Crab-apple jelly with 0.17 per cent acid (as sulfuric)
gave an inversion of 58.8 per cent of the sucrose, whereas orange jelly of
the same acidity gave only 4.9 per cent of sucrose inverted. Since the
inversion is in proportion to the hydrogen-ion concentration if time of
heating is constant, the greatest inversion occurred with the acid giving
the highest hydrogen-ion concentration, the tartaric acid of the grape.
In this instance the total acidity was higher too. Plum with a high total
acidity of 1.35 per cent yielded a lower percentage inverted than the grape
with a total acidity of 0.69 per cent. The plum contains malic acid, which
would result in a lower hydrogen-ion concentration than the tartaric.
Kinds of Sugar Used in Jelly
Most jelly is made with sucrose. There are two sources of sucrose : one,
the sugar beet ; the other, sugar cane.
Cane or beet sugar. For some unexplained reason many persons believe
that jelly cannot be made from beet sugar. Shaw in a series of over 2000
tests found no difference in the two sugars. Lowe and Redfield, working
in a section of the country where many persons believe that beet sugar
will not make jelly, could detect no differences in jellies made from beet
and cane sugar. The sugar was sent from different sections of the state.
In these experiments the source and kind of sugar were not known until
the experiments were finished.
Dextrose. Crystalline dextrose when substituted by weight for sucrose
in a fruit juice yields a jelly similar in texture to that obtained with
sucrose. It is not so sweet as the jelly made with sucrose. In the jelly
made with dextrose, crystallization of the sugar occurs. Crystals usually
begin to form at the top of the surface of the jelly in 24 hours. They
increase until the whole mass is crystallized. The shape of the masses of
crystals resembles coral formation or reminds one of the flowerets of
cauliflower except that they are colored. See Fig. 18. If the glass is full of
jelly the crystals push up the top of the lid and bulge out over the side.
Sometimes the first crystals appear in spots throughout the jelly instead of
on the surface. Sometimes the first crystals are longer than 24 hours in
appearing. If the jelly is turned out of the glass, crystallization occurs
rapidly and the whole mass is usually crystallized in 48 hours or less. If
dextrose is substituted for 50 per cent of sucrose, crystallization may not
occur, and if crystals do appear they are slower in forming. About 50 per
170
JELLY
cent of the jellies made in the author's laboratory with one-half sucrose
and one-half dextrose crystallized.
Levulose. Levulose also forms jelly, but it is more likely to be sirupy,
and if a jelly is formed the sirup must be boiled to 107C., which brings
the levulose nearer to its saturation point.
Maltose. Maltose has been used by the author for gooseberry and cur-
rant jelly. Maltose is considerably less soluble than sucrose and a little
FIG. 18. Jelly made from crystalline dextrose. Showing crystal formation 48
hours after the jelly had been turned out of the glass and 72 hours after the jelly
was made.
less soluble than dextrose at room temperatures. The jelly made with
maltose is very tart and crystallizes as readily, or more so, as jelly made
with dextrose.
Syneresis
Syneresis occurs in some fruit jellies. It is probably more common in
cranberry jelly than in other fruit jellies. Tarr found that, with a hydro-
gen-ion concentration greater than />H 3.1, fluid exuded from the jelly.
Myers and Baker have reported that syneresis in jellies may be brought
about by the hydrogen ion alone, or by the hydrogen ion and cation of
an added salt together, but not by the cation of the salt alone. They
have also reported that the anion of a salt by acting as a buffering agent
may prevent syneresis.
Whether syneresis occurs in a jelly also depends on the source of the
pectin. The writer has never seen syneresis occur with gooseberry jelly,
even when the />H of the jelly is 2.6 or lower. Some citrus pectins made
into jelly show no syneresis at />H 2.0 or lower.
STORAGE OF JELLY 171
The rate of dehydration or setting and mechanical disturbance after the
jelly starts to set may also influence syneresis.
Temperature for Boiling Sirup for Jelly
If the boiling point of sugar solutions is referred to, p. 49, it is found
that a sugar solution containing 60 per cent of sugar boils at 103.0C.,
and a 70 per cent solution boils at 106.5C. A jelly boiled to 103C.
would contain approximately 60 per cent of sugar, and one boiled to
106.5C. would contain approximately 70 per cent of sugar. Evidently, a
jelly cooked to a temperature between these two temperatures would con-
tain between 60 and 70 per cent of sugar.
Cruess and McNair have reported that jellies containing amounts of
sugar indicated by boiling to 65 Brix give a good concentration for jelly.
A solution of sugar of 65 Brix boils at sea level at 103.9C. Cruess and
McNair state that if, to the boiling point of water of any locality, 3.9C.
or 7.02F. is added, a suitable boiling point for jelly will be obtained
for that locality.
The directions in the laboratory outline state to boil the sirup to a
temperature of 103C. for jelly. This is for a location where the water
boils at 99C. This is sufficient for fruit juices that contain a high per-
centage of pectin and have a high acidity. This would give approximately
60 per cent of sugar in the finished jelly. Some juices with a low acidity
and pectin content will yield better jelly if boiled to a higher temperature
than 103C. A temperature between 104 and 105C. yields a jelly with
a sugar content of about 65 per cent. If they do not jell with a tempera-
ture of 105 to 106C. the juice does not contain sufficient pectin or acid.
Jelly test. The method of housekeepers of determining when jelly is
boiled sufficiently is to let a portion of the sirup drop from a spoon.
When the sirup "sheets" off the spoon the jellying temperature has been
reached.
Storage of Jelly
Jelly deteriorates in flavor on standing. Freshly made jelly has a better
flavor and aroma than jelly that has been made and stored for some time.
The cooking causes some decomposition of flavoring products. In stand-
ing, some of the aromatic substances and flavoring substances are volatil-
ized and some are probably lost by decomposition.
Storage, mold, and sugar concentration. With too high a percent-
age of sugar, crystallization of the sugar may occur. With too low a concen-
tration, the jelly will mold more readily. It will also ferment more readily
than a jelly with a higher concentration of sugar. Singh has reported that
jellies made with less than 65 per cent of sugar molded unless the jelly
containers were sterilized.
172 JELLY
Sterilization of the glasses, and having them dry and hot when the
jelly is added, probably aid in preventing mold and also fermentation.
Running melted paraffin over the top of the jelly so that it forms a com-
plete seal is an aid in keeping it.
Definition of Jelly
This chapter would be incomplete without giving Goldthwaite's defini-
tion of an ideal jelly. "Ideal fruit-jelly is a beautifully colored, transparent,
palatable product obtained by so treating fruit-juice that the resulting mass
will quiver, not flow, when removed from its mold ; a product with texture
so tender that it cuts easily with a spoon, and yet so firm that the angles
thus produced retain their shape; a clear product that is neither sirupy,
gummy, sticky, nor tough ; neither is it brittle and yet it will break, and
does this with distinct beautiful cleavage which leaves sparkling character-
istic faces. This is that delicious, appetizing substance, a good fruit-jelly."
LITERATURE CITED AND REFERENCES
Ahmann, C. F., and Hooker, H. D. The Estimation of Pectin and a Study of the
Constitution of Pectin. Mo. Agri. Expt. Sta. Research Bull. 77. (1925).
Askew, H. O. Changes in the Chemical Composition of Developing Apples. J.
of Ponology and Hort. Sci. 8: 232 (1935).
Baker, G. L. A New Method for Determining the Jellying Power of Fruit-Juice
Extractives. Food Ind. 6: 305 (1934).
Campbell, C. H. Jelly. Ind. Eng. Chem. 12: 558. (1920). Also in Am. Food J.
15: 24. (1920).
Carre, M. H., and Haynes, D. The Estimation of Pectin as Calcium Pectate and
the Application of this Method to the Determination of the Soluble Pectin in
Apples. Biochem. J. 16: 60. (1922).
Chernoff, L. H. Pectin, Jelly-Making and Sugar. Am. Food J. 18: 200. (1923).
Conrad, C. M. A Furfural-Yielding Substance as a Splitting Product of Proto-
pectin During Ripening of Fruits. Plant Physiology 5: 93. (1930).
Cox, R. E. Cranberry Jelly. Food Ind. 5: 348 (1933).
Cruess, W. V., and McNair, J. B. Jelly Investigations. Ind. Eng. Chem. 8:
417 (1916).
Denton, M. C., Johnson, R., and Yeatman, F. W. Homemade Apple Citrus
Pectin Extracts and Their Use in Jelly Making. U. S. Dept. Agri., Circular
254 (1923).
Dore, W. PI. The Pectic Substances. J. Chem. Ed. 3: 505 (1926).
Dore, W. H. Recent Progress in the Chemistry of Pectin and Its Industrial
Application. Ind. Eng. Chem. 16: 1042 (1924).
Dore, W. H. Definitions Written by the Committee on Nomenclature of Pectin
of the Agricultural Food Division. Proc. Am. Chem. Soc. 49: 37 (1927);
J. Am. Chem. Soc. 49 (1927).
Fellenberg, T. H. von. Uber die Konstitution der Pektinkorper. Biochem. Zeitsch.
85: 118 (1918).
Goldthwaite, N. E. Contribution on the Chemistry and Physics of Jelly-Making.
Ind. Eng. Chem. 1: 333 (1909).
Goldthwaite, N. E. Contribution on Jelly-Making. Ind. Eng. Chem. 2: 457 (1910).
Goldthwaite, N. E. Principles of Making Fruit-Jellies. Colorado Agri. Expt. Sta.,
Fort Collins, Colo. Bull. 298 (1925).
REFERENCES 173
Haller, M. H. Changes in the Pectic Constituents of Apples in Relation to Sof-
tening. J. Agri. Research 39: 739 (1929).
Halliday, E. G., and Bailey, G. R. Effect of Calcium Chloride on Acid-Sugar-
Pectin Gels. Ind. Eng. Chem. 16: 595 (1924).
Jameson, E. Requirements of Pectin for the Commercial Jelly Maker. Ind. Eng.
Chem. 17: 1291 (1925).
Johnston, R., and Denton, M. C. The Relation of Alcohol Precipitate to Jelly-
ing Power of Citrus Pectin Extracts. Ind. Eng. Chem. 15: 778 (1923).
Lowe, B., and Redfield, G. M. Iowa Grown Beet Sugar Equals Any Sugar.
Iowa Agri. Expt. Sta., Bull. 135 (1926).
Myers, P. B., and Baker, G. L. Fruit Jellies. IV. The Role of Salts. Univ.
of Del. Agri. Expt. Sta., Bull. 144. Technical Bull. No. 7 (1926).
Myers, P. B., and Baker, G. L. Fruit Jellies. V. The Role of Pectin. I. The
Viscosity and Jellying Properties of Pectin Solution. Univ. of Del. Agri.
Expt. Sta., Bull. 149. Technical Bull. No. 8 (1927).
Norris, F. W., and Schryver, S. B. The Pectic Substances of Plants. III. The
Nature of Pectinogen and Its Relation to Pectic Acid. Biochem. J. 19: 676
(1925).
Olsen, A. G. Pectin Studies. I. Citrus Pectin. Ind. Eng. Chem. 25: 699 (1933).
Olsen, A. G. Pectin Studies. III. General Theory of Pectin Jelly Formation.
J. Physical Chem. 38: 919 (1934).
Rooker, W. A. Fruit Pectin. Its Commercial Manufacture and Uses. Avi Pub-
lishing Co., N. Y. (1928).
Schryver, S. B., and Haynes, D. The Pectic Substances of Plants. Biochem.
J. 10: 539 (1916).
Shroger, A. W. The Chemistry of Cellulose and Wood. McGraw-Hill Co.
(1926).
Shaw, G. W. Packing Prunes in Cans. Cane Sugar <vs. Beet Sugar. Cal. Expt.
Sta., Circular 33 (1907).
Singh, L. A Study of the Relation of Pectin and Acidity in Jelly Making. Ind.
Eng. Chem. 14:710 (1922).
Spencer, G. The Formation of Pectin Jellies by Sugar. J. Physical Chem. 33:
1987 (1929).
Spencer, G. The Effect of Salt on Sugar-Pectin Jelly-Formation. J. Physical
Chem. 33: 2012 (1929).
Spencer, G. The Relation between Acids and Pectin in Jelly Formation. J.
Physical Chem. 34: 410 (1930).
Spencer, G. The Purification and Estimation of Pectin. J. Physical Chem. 34:
429 (1930).
Spencer, G. The Manipulation of Jelly Strength-Testing Apparatus. J. Physical
Chem. 34: 654 (1930).
Sucharipa, R. Experimental Data on Pectin-Sugar-Acid Gels. J. Assoc. Of-
ficial Agri. Chem. 7: 57 (1923).
Tarr, L. W. Fruit Jellies. The Role of Acids. Univ. of Del. Agri. Expt. Sta.,
Bull. 134, Technical Bull. No. 2. (1923).
Tarr, L. W., and Baker, G. L. Fruit Jellies. II. The Role of Sugar. Univ. Del.
Agri. Expt. Sta., Bull. 136, Technical Bull. No. 3 (1926).
Tarr, L. W. Fruit Jellies. III. Jelly Strength Measurements. Univ. of Del.
Agri. Expt. Sta., Bull. 142, Technical Bull. No. 5 (1926).
Tarr, L. W. Fruit Jellies. Chapter 26, Colloidal Behavior. Edited by Bogue,
McGraw-Hill Co. (1924).
Tarr, L. W. Fundamentals of Fruit Jelly Formation. Canning Age 5: 684
(1924).
174 JELLY
Tolman, L. M., Munson, L. S., and Bigelow, W. D. The Composition of Jellies
and Jams. J. Am. Chem. Soc. 23: 347 (1901).
Wilson, C. P. The Manufacture of Pectin. Ind. Eng. Chem. 17: 1065 (1925).
JELLY
Directions for preparing fruit for jelly. Apples and crab-apples are
washed but not pared. Remove bad spots and wormy places but retain
the seeds and core, as they contain pectic substances. Cut in rather small
pieces in order to more easily extract the pectin. Gooseberries and cur-
rants are washed but do not need to be stemmed. Add sufficient water
to cover apples and crab-apples. Green gooseberries can be covered with
water; ripe ones should be only partially covered. For most berries about
y\ cup of water to a pint of berries is sufficient, or else the pectin of the
juice will not be sufficiently concentrated. Cranberries may be used. Rather
ripe cranberries should have a smaller proportion of water than less ripe
ones. Drain the juice through a heavy cloth bag. Save the pulp for a second
extraction. Water-packed canned gooseberries are excellent to use, as they
are easily obtained at any time of the year. The number ten size is more
economical. In using the canned gooseberries the juice is not cooked for
the first extraction but drained without heating.
Experiment 23.
A. To determine the pectin content of fruit juice.
To 45 or 60 cc. of alcohol in a graduate add 15 cc. of the juice to be tested.
Invert the graduate slowly and turn back. A precipitate in a mass indicates
enough pectin for jelly. Pour out in a dish and lift the pectin. (See p. 157.)
If a quantitative test is desired, follow some standard directions for pectin
determinations.
B. Test the juice with a jelmeter. Add sugar and cook according to direc-
tions furnished with the jelmeter. Compare the jellies with those made from
the same juice under Experiment 24.
Experiment 24.
To determine the effect of varying the proportion of sugar to juice in making
jelly.
Use a first extraction of juice. Use 240 grams of juice for a cup and 200
grams of sugar per cup. Add the sugar to the juice and boil until the tempera-
ture is 103C. Be sure that the temperature reaches 103C. before removing
from the stove; read to just above the 103 mark on the thermometer rather
than below it. Pour into hot, dry, sterilized jelly glasses. Sterilize by boiling in
hot water, then set in a place where they will stay hot before adding the jelly.
With more than Y\ cup of sugar to a cup of juice, two of the 8-ounce jelly
glasses will be needed to hold the jelly. If the percentage of sugar is to be
determined in the finished jelly, weigh the pan and spoon before the juice
is added. Weigh the pan, spoon, and contents on a balance as soon as the
temperature of 103C. has been reached, then pour into jelly glasses. Determine
JELLY
175
the approximate yield of the jelly in cups by filling other jelly glasses with
water to the same height as the jelly and then measure the water. This elimi-
nates pouring the jelly into measuring cups and then into the jelly glasses.
1. Boil 2 cups of fruit juice without the addition of sugar until the desired
temperature is reached. Does it give the spoon jelly test? Obtain the volume,
and label it, and set aside to jell. It is best to put this quantity of juice in a
large pan so that it may boil rapidly, without boiling over. When the juice
is concentrated to about j/2 cup it may be transferred to a smaller pan, as the
quantity of juice at the end of the experiment is so small that it is difficult to
get an accurate reading with the thermometer.
2. To 1 cup of juice add % cup of sugar. Cook until a temperature of
103C. is reached. Pour into jelly glass. Obtain volume, label it, and set aside
to jell.
3. To 1 cup of juice add Y 2 CU P f sugar. Follow directions under 2.
4. To 1 cup of juice add Y\ cup of sugar. Follow directions under 2.
5. To 1 cup of juice add 1 cup of sugar. Proceed as in 2.
6. To 1 cup of juice add \Y\ cups of sugar. Proceed as in 2.
7. To 1 cup of juice add \Y 2 cups of sugar. Proceed as in 2. Omit 7 if the
alcohol test was not exceptionally rich in pectin.
Temperature
Cooked to
Yield,
cups
Per cent of sugar
in finished jell
Color
Texture
Flavor
Results and conclusions.
Experiment 25.
To determine the effect on the texture of jelly when the juice is not as
rich in pectin as in Experiment 24.
To the fruit pulp left from the first extraction of the juice, add water to
barely cover and heat for a few minutes. Drain through a heavy cloth. What-
ever the percentage of pectin in the juice in Experiment 24, there will be less
pectin in the second extraction. Repeat directions under 24, 2.
1. To 1 cup of juice add Y(- cup of sugar.
2. To 1 cup of juice add Y 2 CU P f sugar.
3. To 1 cup of juice add Y\ CU P f sugar.
4. To 1 cup of juice add 1 cup of sugar.
5. To 1 cup of juice add 1^4 cups of sugar.
Compare the resulting jellies with those of Experiment 24.
Temperature
Cooked to
Yield,
cups
Per cent of sugar
in finished jell
Color
Texture
Flavor
Results and conclusions.
176
JELLY
Experiment 26.
To determine the effect of boiling the jelly to a greater concentration.
Use juice from the first extraction. Compare the texture, volume, and per-
centage of sugar in the finished product with jelly from Experiment 24, 2,
with the same proportion of sugar.
1. To 1 cup of juice add ^4 cup of sugar. Cook to 104.5C. Proceed as in
Experiment 24, 2.
2. To 1 cup of juice add ^4 cup of sugar. Cook to 106. 5C. Proceed as in
Experiment 24, 2.
3. To 1 cup of juice add 1 cup of sugar. Cook to 104.5C. Proceed as in
Experiment 24, 2.
4. To 1 cup of juice add 1 cup of sugar. Cook to 106. 5C. Proceed as in
Experiment 24, 2.
Temperature
Cooked to
Yield,
cups
Per cent of sugar
in finished jell
Color
Texture
Flavor
Results and conclusions.
Experiment 27.
To determine the effect of cooking slowly on the color of the jelly.
1. To 1 cup of juice add Y\ cup of sugar. Cook to 103C. Cook quickly.
Proceed as in Experiment 24, 2.
2. To 1 cup of juice add ^/\ cup of sugar. Cook slowly and cook until a
temperature of 103C. Proceed as in Experiment 24, 2.
Yield
Color
Texture
Flavor
Results.
Experiment 28.
To determine the effect of using different kinds of sugar in making jelly.
1. To 1 cup of juice add ^4 cup of sucrose. Cook to 103C. Proceed as in
Experiment 24, 2. Use as a control.
2. To 1 cup of juice add 150 grams of crystalline dextrose. What is the
measure of the dextrose? Cook to 103C. Proceed as in Experiment 24, 2.
3. To 1 cup of juice add 150 grams of levulose sugar. What is the measure
of the levulose? Cook to 103C. Does it jell?
4. Repeat 3, but cook to 107C.
5. To 1 cup of juice add 150 grams of maltose. Cook to 103C.
JELLY
177
Temperature
Cooked to
Yield,
cups
Per cent of sugar
in finished jell
Color
Texture
Flavor
Results and conclusions.
What happens to the jellies in Experiment 28 after standing a few days?
If crystals appear, how long does it take for them to form?
When the juice contains a smaller proportion of pectin, how does the texture
of the jell compare for any definite proportion of sugar with that of jell made
of a juice richer in pectin? What is the effect on the texture of the jelly of
cooking the sirup to a higher temperature or concentration? Which propor-
tion of sugar in Experiment 24 produces the best-textured jelly? Would this
proportion hold for all juices? Why? What is the effect on the texture of the
jelly when the proportion of sugar used is too small? On the flavor? What is
the effect on the texture when the proportion of sugar is too great? On the
flavor?
What is the result of substituting dextrose or levulose for sucrose on the
texture of the jelly? On the flavor?
CHAPTER VI
GELATIN
Gelatin has been used extensively for experimental work in studying the
reactions of colloidal substances, particularly in connection with gel forma-
tion.
Uses of gelatin in foods. In food preparation gelatin is used as a basis
to make a flavored gel for salads and desserts. It is used as an emulsi-
fying agent, to form a basis for some types of candy like marshmallows,
and it is used in frozen desserts.
Source of gelatin. Gelatin is obtained from collagen by hydrolysis.
Collagen is a protein and is found in connective tissue, tendons, cartilage,
in the organic part of bone tissue, in the inner layer of skin of animals,
and in fish skins, scales, and "sounds" or fish bladders. Collagen is not found
as a pure substance in these tissues, but in combination with inorganic ma-
terials and with other proteins like elastin, mucin, mucoid, etc. White con-
nective tissue is found between the muscle fibers, in tendons, and in the
inner layers of skin. It contains a high percentage of collagen. The jelly-
ing of meat broth after cooling is due to the gelatin, which has been formed
from the collagen of the connective tissue. Sometimes the concentration
of the gelatin in the broth is not great enough to bring about the formation
of a gel. When pieces of baked fish skins are allowed to cool on the baking
pan, they adhere to it quite tenaciously, because of the adhesive quality
of the gelatin or glue formed from the collagen of the fish skin.
Distinction between Gelatin and Glue
Commercially there is little distinction between gelatins and glues, ex-
cept that edible gelatin is a high-grade product and complies with the Pure
Food Laws. It contains only traces of harmful ingredients, and Bogue
states that it should be made from "such stock and by such sanitary
methods, as not to be objectionable from the ethical point of view." Glue
may be made from the same type of stock as the gelatin, but usually no
effort is made to remove impurities.
Manufacture of gelatin. In making edible gelatin the stock is or
should be selected w r ith greater care than for inedible gelatin or glue. Some
edible gelatins are made entirely from bones. Others are made from calf-
skin and others from pork skin. The bones of young animals contain more
collagen than bones from older animals. For edible gelatin the bones are
178
ACIDS 179
washed to free them from dirt, then degreased by extraction of fat by fat
solvents. Next the soluble lime salts are removed by leaching the bones
with acid. The principal salts in bone are the calcium phosphates, but some
calcium carbonate and magnesium phosphate are also found. It is difficult
to free the bones from all the traces of inorganic matter, and the elec-
trolytes left influence the />H of the resulting gelatin. The degreased bone
with the inorganic salts removed is known as ossein and contains the col-
lagen from which the gelatin is made. The ossein is soaked in lime water.
In the lime water and in acid solution the collagen swells. This swelling
makes it possible to hydrolyze the collagen to gelatin at lower temperatures
than would otherwise be possible. This is important in the manufacture of
gelatin, for with higher temperatures or long heating the jellying strength
of the gelatin is lessened. The gelatin is then dried. The gelatin thus
obtained has some ash and is not at the isoelectric point, but on either the
acid or alkaline side of the isoelectric point. Putrefaction by bacteria must
be prevented during the manufacturing process, as the bacterial action
lowers the grade of gelatin obtained and odors develop that remain in
the finished gelatin even if putrefaction is later stopped.
Market types of gelatin. Gelatin is put upon the market in three
forms: granulated, pulverized, and sheet. The granulated is the form most
commonly obtained.
Sheppard and Hudson have reported a new form of gelatin. It is called
pressed foam gelatin. It is said to absorb water rapidly and to dissolve
rapidly and it is not excessively bulky.
Hydrolysis of Collagen
Temperature. When collagen is heated with water, gelatin is formed.
Bogue states that this occurs at 80 to 90C. or at higher temperatures. The
reaction occurs more rapidly at higher temperatures, but at these tempera-
tures more of the gelatin is hydrolyzed to proteoses, peptones, or amino
acids. When meat is cooked in hot water the collagen of the connective
tissue is converted to gelatin. The gelatin is soluble in the hot water, and
as it is dissolved the muscle fibers are separated and fall apart. At tem-
peratures below the boiling point of water a longer time is required to
hydrolyze the collagen to gelatin.
Acids. The addition of a dilute acid hastens the hydrolysis of collagen,
but this also increases the hydrolysis of the gelatin to peptones and amino
acids. The latter products do not form gels, so that, in the manufacture
of gelatin, it is not desirable for the gelatin to contain very much of these
products. Softening of connective tissue in cooking meat is brought
about in a shorter time by the addition of a small amount of acid.
Tomatoes added to a stew will accomplish this purpose. Sometimes vinegar
is used.
180 GELATIN
Properties of Gelatin
Gelatin is characterized by forming a solution in water at high tem-
peratures and, with high enough concentration, a gel at low temperatures.
The dry gelatin has a slightly yellow cast and contains from 10 to 18
per cent of moisture. It swells when put in cold water, the degree of
swelling being modified by acids, alkalies, or salts. It dissolves at about
35 C., and it gels at low temperatures, the exact gelation temperature
depending upon the concentration and time of standing.
Swelling and Solution
The extent to which gelatin swells in water is modified by the surface
area, its initial />H, the presence of or addition of acids, alkalies, and in-
organic salts, and its previous history. Bogue states that gelatin tends to
absorb water equal to the amount of water it held at the last warming,
but not very much over this. Thus the degree of swelling is modified by
the previous history of the sample. This would include treatment during
manufacture.
Ease of hydration of gelatins. The pulverized gelatin swells most
rapidly, for it is finely divided, hence has a greater surface area. Granu-
lated gelatin absorbs water quickly, not so rapidly as pulverized, but rapidly
enough so that it is easily used in the home. Sheet gelatin may be thin or
rather thick. The thin form is easily hydrated, but the thick does not
hydrate so readily, and therefore requires longer soaking in cold water or
a longer period of heating to dissolve. In preparing gelatin dishes the gela-
tin is usually allowed to soak in a small amount of cold water. During
this soaking it swells. Bogue suggests that this swelling, by the formation
of capillary spaces in the interior of the gelatin particles, increases the
surface of the gelatin.
Solution. According to Bogue, soaked gelatin goes into solution more
rapidly than unsoaked gelatin owing to solution occurring from the outer
and inner surfaces, whereas if gelatin is put in hot water before soaking,
swelling is inhibited to a certain degree and solution takes place from the
outer surface only. The process of solution may be analogous to hydrolysis
of collagen, i.e., just as gelatin is formed more readily from the swollen
collagen, so solution may take place more readily from the swollen gelatin.
Very little of the gelatin goes into solution while it is soaking in cold
water. When the temperature is increased to about 35 C. the gelatin goes
into solution rapidly. For food preparation this is often accomplished by
adding hot water to the hydrated gelatin. It can also be accomplished by
melting the hydrated gelatin over hot water and then adding cold water
or fruit juices.
GELATION AND STIFFENING POWER OF GELATIN 181
Initial pH. Bogue states that ordinary gelatin usually has a />H about
7. The pH of different commercial brands used in the laboratory for food
preparation has been found to vary from pH 5 to 7. The isoelectric point
of gelatin is given as pH 4.7. At this point it is least soluble, least ionized
and swells the least. Bogue has found turbidity and foaming to be at a
maximum at the isoelectric point. Loeb states that 1 gram of dry gelatin
at the isoelectric point absorbs 7 grams of water. As the pH is decreased
below 4.7 or increased above 4.7, greater absorption of water occurs until
a maximum is reached. Bogue states that it is desirable from the standpoint
of solubility for the gelatin to have a />H of 3.0 to 3.5, or 8 to 9. The
variation of the />H of commercial gelatins is due to differences in salt
content, which may increase the acidity or alkalinity. This acidity due to
electrolytes, or to the treatment in acids and alkalies during manufacture,
is often referred to as the residual acidity or alkalinity of the gelatin.
Acids. At a />H below 4.7 the amount of water absorbed increases with
increasing acidity until a maximum is reached at a pH of about 3.5. As
the pH is lowered more than 3.5, the amount of water absorbed decreases.
Loeb states that at a />H of 3.2 to 3.5 a gram of dry gelatin absorbs about
35 grams of water. In food preparation the acid fruit juices are added
after the gelatin is in solution, so that the extent of swelling during hydra-
tion is affected by the initial acidity of the gelatin. In gelatin mixtures that
contain acid salts, as acid phosphates and citric acid added for flavoring,
the amount of swelling would be affected by the acidity.
Alkalies. Alkalies have the same effect as acids upon the swelling of
gelatin, except that it is not so pronounced. Bogue states that the maxi-
mum swelling on the alkaline side is at /H 9.
Salts. Salts also affect the water absorption of gelatin. Some salts in-
hibit the swelling and others favor it. Ostwald states that when salts and
acids are combined the salt usually decreases swelling below the amount
which would result in the presence of acid alone, even though the salt
alone may increase swelling. Sugar decreases swelling. Loeb states that, if
the />H of the solution is kept constant, all ions of the same valency and
charge have nearly the same depressing effect upon swelling. The depress-
ing effect increases with increasing valency.
Gelation and Stiffening Power of Gelatin
Gelation is the formation of a gel or solidification of a gelatin solution.
In food preparation it is referred to as the setting of the gelatin. The
setting point is no clearly defined point. The gelatin solution becomes
sirupy, like a thick sugar solution, then gradually thickens to finally form
a firm gel. Thus there is no distinct point at which solidification occurs.
If samples of solutions are placed in test tubes, the time at which they
cease to flow may be taken as the setting point. In larger containers this
is not so easy to ascertain, and it is necessary for members of the class to
182 GELATIN
compare results and all try to select a definite stiffness as the setting point.
Sheppard and Sweet devised an apparatus for determining the setting point.
They take the setting point as the point at which a stream of air bubbles
ceases to flow through the gelatin solution.
The stiffening power and the viscosity of gelatin are affected by several
factors. Usually stiffening power and viscosity run parallel, but this is
not always true, for gelatins giving the highest viscosity do not always
yield the stiffest jellies. Viscosity of gelatin is measured at a temperature
of 35 C. by some workers and at 60 C. by others. At these temperatures
gelatin is a liquid and will flow. Viscosity is measured by the rate of flow
under standardized conditions; stiffening power or jelly strength is meas-
ured when the gelatin is set.
Different brands of gelatin show decided differences in stiffening power
when made into gelatin to serve. If two gelatins cost the same per pound,
one may be more economical than the other, if equal quantities of the
gelatins when combined with the same amounts of sugar, water, and flavor-
ing show different stiffening power.
Time, concentration, and temperature all affect the gelation process and
the stiffness of the resulting jelly.
Time of gelation. When concentration and temperature are constant
a definite length of time is necessary for gelation to occur. This is character-
istic of many colloidal changes. With lessened concentration a longer time
is required for gelation. At higher temperatures a longer time is required
for the solidification to take place.
The firmness of the jelly is also affected by time. Some time may be
required after the gelatin solution has cooled to the refrigerator tempera-
ture before gelation occurs. The jelly becomes stiffer with longer standing.
Gelatins allowed to stand in the refrigerator over night at a temperature
of 8 to 10C. are stiffer than those standing only a short time after
gelation has occurred. Clark and Du Bois state that after gelatin has cooled
3 hours at 0C. little or no further increase in jelly strength occurs.
Dahlberg, Carpenter, and Hening found that, for the weak gelatin solu-
tions used in ice cream, gel formation requires a long period of time. They
allowed 18 hours for gel formation and aging in most of their experiments.
However, they found that the gumminess in ice cream due to too much
gelatin increased during 4 to 5 weeks' storage of the ice cream. They
attributed this to the "slow rate at which gelatin gels in weak concentra-
tions come to a final equilibrium."
Concentration. With a definite temperature and time, solidification
occurs only with a definite concentration. With increasing concentration
of gelatin the time for setting is shortened. The amount of liquid that
a gram of dry gelatin can bind and hold in the form of a gel is high, 1 to
2 grams forming a gel with 99 to 98 grams of water.
Ostwald states, that the solidification of gelatin in J^ hour depends upon
the mode of preparation, but usually requires about 2 per cent at 15C.
"SEEDING" GELATIN SOLS 183
and 1 per cent at 0C. To serve as food the concentration should not be
too high, or the jelly is too stiff to be desirable. Some food gelatins pro-
duce a desirable texture for serving with a 1.5 per cent concentration,
some require 2 per cent, and some may require as much as 3 or 4 per cent.
Manufacturers often place a quantity of gelatin in a packet or envelope
and state the amount of water to be used with it. This amount of water
is an average amount required under all conditions for cooling. In some
instances it might be desirable to change it, on account of variation in
proportion of ingredients or variation in temperatures at which it solidifies,
or for other reasons. Recipes containing sauces thickened with egg or
starch do not need so high a concentration of gelatin.
It is preferable to use bulk or sheet gelatin by weight, rather than by
measure. On account of differences in the size of the gelatin particles,
a definite measure does not yield the same weight, hence a different concen-
tration of the gelatin w r ould be used.
Temperature. With a definite concentration and time for setting, solidi-
fication occurs only with a definite temperature. For a high solidifying
temperature a high concentration of gelatin is required. The slower a
gelatin solution is cooled, the higher the temperature at which it solidifies.
A gelatin solution may be cooled down, by packing ice around its container,
to a temperature below that at which setting would occur if a longer
time is allowed. On the other hand, gelatin solutions may be mixed and
left standing for 2 or 3 hours at room temperature. If they are then put
in ice or the refrigerator they set quite rapidly and as if gel nuclei might
have started to form while standing at room temperature. At low tempera-
tures all gelatins become firmer. At high temperatures they are liquid,
for no gel occurs at temperatures above 35 C. with any concentration of
gelatin. With the same concentration one gel may set at 10C., another
at 12, still another at 14 to 16C., and others require lower tempera-
tures for setting. The gelatins that set at higher temperatures show jellies
of greater firmness than those that set at low temperatures. The ones
requiring lower temperatures than 10C. to set do not serve very well,
for they also soften at a low temperature.
Addition of solidified gelatin to a gel solution. Lloyd states that
gelation is similar to crystallization, in that it takes place from a saturated
solution. There are various theories to account for gel formation. It has
been suggested that nuclei, strands, rods, or micelles form in the solution
and solidification takes place upon cooling, with the formation of a gel
structure. If some gelatin that has solidified is added to freshly made
gelatin solution solidification takes place more rapidly. Alexander suggests
that this is due to the addition of nuclei, and that other particles aggregate
around these nuclei. This is similar to "seeding" or adding of crystals to
crystalloidal solutions to hasten crystallization. Dahlberg, Carpenter, and
Hening find that this property of gelatin has a practical application in
ice-cream making. The gelatin is added to ice cream to improve the texture
184 GELATIN
and body of the ice cream. If the unfrozen ice-cream mix is aged at a
temperature just above the freezing point a smoother ice cream is obtained.
One reason attributed for this is the low viscosity of the freshly made
gelatin solutions compared with the viscosity of the aged solutions, and
another is the speed at which the gelatin gel previously aged reforms
after whipping during freezing.
Hydrogen-ion concentration. The acidity of the gelatin affects its
stiffening power. According to the kind and amount of ash and its buffer
action the gelatin may have a hydrogen-ion concentration greater or less
than its isoelectric point, which is pH 4.7. The initial pH of different
brands and samples tried in the laboratory has been above the isoelectric
point. Probably the greater the acidity or alkalinity, unless it is beyond the
maximum or minimum pH for the greatest water absorption, the less firm
the resulting jelly. However, the />H of a gelatin solution does not entirely
control the time for setting or the stiffness of the resulting gelatin. Two
gelatin solutions may have the same />H and the same proportions of ingredi-
ents added, but one may require much longer than the other to set and never
produce as firm a jelly.
Acids and alkalies. The addition of fruit juices or acid salts to the
gelatin solution increases its acidity, the increase depending on the acidity
of the fruit juice added, its buffer capacity, and the quantity added. Lemon
juice has a lower />H than most fruit juices. Its />H varies slightly but
is usually between 2.0 and 2.5. The addition of % cup of lemon juice
to y 2 ounce of gelatin with an initial />H 6 to 6.5, 3^2 cups of water and
T /2 cup of sugar, lowers the pH of the mixture around 3. This is lower
than the isoelectric point of the gelatin. Many recipes use larger quantities
of lemon juice than the proportion given above. This would increase the
acidity still more. With a definite concentration of gelatin a less firm jelly
is obtained as the amount of lemon juice is increased. A longer time is
also required for the gelatin to set with the increased lemon juice or
acidity.
Patten and Johnson found that a 3 per cent gelatin solution liquefied
on standing when the />H was sufficiently low. Liquefaction also varied
with the temperature. It occurred at a temperature of 18C. when the
gelatin solution was at />H 3.6 or lower.
Some of the less acid fruit juices do not increase the acidity of the gelatin
mixture as much as the lemon juice. The addition of fruit or vegetable
juices such as tomato juice may bring the pH of the gelatin close to its
isoelectric point. The />H of tomato juice varies somewhat but is usually
between 4.2 and 4.8. The juices that bring the gelatin close to the isoelec-
tric point do not increase the time required for gelation to the extent that
the lemon juice does. Gelatin made with tomato juice varies in the length
of time required for setting. But in recipes lemon juice is usually added
in combination with other fruit juices, and either lemon or vinegar is
often added with tomato juice for tomato gelatins. Recipes containing a
SUGAR 185
larger quantity of a very acid fruit juice may need a higher concentration
of gelatin to produce a texture desired for serving.
Lemon jellies were made from the same sample of gelatin, using different
proportions of lemon juice. When the quantity of lemon juice added was
just sufficient to bring the hydrogen-ion concentration of the mixture to
about pH 4.7, the isoelectric point of gelatin, the jelly formed was cloudy
and more turbid than when the />H of the mixture was lower than 4.7.
Jellies with a pH lower than the isoelectric point of gelatin were clear
and sparkling. They also required a longer time for the gel to form than
those with a higher />H. When the series was repeated but citric acid was
substituted for lemon juice, similar results were obtained.
Tartaric acid added to the gelatin solution also increases the time for
gelation. A teaspoon of tartaric acid (about 3.5 grams) or a teaspoon of
citric acid (about 3.5 grams) added to 3.5 grams of gelatin and 236.5 cc.
of water gives the mixture about />H 2.7. The jellies are clear and tart.
Patten and Johnson have reported that a 3 per cent solution of gelatin
at 20 to 22C. begins to liquefy between a pH of 8.4 and a pH of 9.2.
It is not completely fluid at />H 9.6.
Salts. It has been reported by several investigators that the gelation tem-
perature is affected by electrolytes. The effect is usually given as follows
for anions at equal concentrations. The first of the series elevates the
gelation temperature, and it is slightly lower for each following anion,
until the iodide may lower the gelation temperature below 0C. SO >
citrate > tartrate > acetate > Cl > C1O 3 > NO 3 > Br > I. This is the
order above the isoelectric point. When enough lemon juice or acid has been
added so that the reaction is below the isoelectric point the cations may have
more effect than the anions. The order of anions given above indicates that
some salts would increase the tenderness of gelatin gels whereas others
would increase the gel strength.
Dahlberg, Carpenter, and Hening found that the gel strength was
greater in milk than in water, even when the proportion of gelatin added
to the milk was based on the water content of the milk and not on its total
volume or weight. They found that the change in hydrogen-ion concen-
tration did not account for this increase in jelly strength in all the samples.
The other factors that might influence the jelly strength were the salt
and protein content of the milk. They state that the "influence of salts
on gel strength has been observed by other investigators, so it may be one
of the means by which skim milk altered gel strength."
Sugar. Small amounts of non-electrolytes do not appreciably affect
the viscosity of gelatin solutions, but in large quantities sugar increases
the viscosity, as a thick sugar sirup is more viscous than a thin one. Loeb
has reported that cane sugar does not diminish the viscosity of gelatin solu-
tions, but at concentrations of M/S or over may increase it slightly. The
sugar has a similar effect upon the stiffening power. Some concentrations
of sugar do not seem to affect the stiffening power, but others do. Ostwald
186 GELATIN
states that 1 gram of sugar added to 9 cc. of a 6 per cent gelatin solution
accelerates gelation. This would give about 10 per cent of sugar in the
solution. Larger quantities of sugar may retard gelation.
Opacity in gelatin. Edwards states that two factors of prime impor-
tance in gelatin are its strength and clarity of aqueous solution. In regard
to clarity he says that many perplexing problems occur in this connection,
for a gelatin may be clear at one concentration but, if further diluted,
may appear turbid. He says that a complete explanation of the problem
of turbidity has yet to be made, but some causes are as follows : ( 1 ) actual
dirt, particles of animal tissue and fibers, (2) mold, (3) emulsified grease
and calcium salts of fatty acids, (4) protein salts and proteins other than
gelatin which precipitate and remain in suspension when the />H of the
solution is varied, (5) a calcium sulfate-phosphate complex which is re-
tained in solution by the presence of sulfurous acid, and (6) colloidal sulfur.
Edwards states that the first two enumerated difficulties should not be
present and when detected the gelatin should be condemned. Emulsified
grease is more difficult to remove. It results from the employment of
greasy material, extraction of gelatin at the wrong />H, the agitation of
liquid in the boiling vat, and improper filtration. The presence of proteins
other than gelatin is more likely to occur in a skin gelatin. Mucin and
chondrin are readily soluble in weak alkalies and are thrown out of solu-
tion by acids. Hence they are less likely to be found in acid gelatins.
Cloudiness due to the presence of insoluble calcium sulfate-phosphate com-
plex is more likely to be found in ossein gelatins. Colloidal sulfur is more
likely to be found in glue than in gelatin stock.
Gelatin is used in the meat trade for packing tongues, chickens, and
glazing hams. Sometimes a cloudy precipitate appears which is caused by
too much calcium in the gelatin.
Black mentions that unless the copper content of the gelatin is low a
purplish discoloration may appear with meats and particularly with
chicken and tongues.
Another cause for turbidity is discussed by Clayton. At the isoelectric
point the gelatin solutions always show more turbidity, a 400 per cent
increase in turbidity occurring with a />H variation of 0.03 (/>H 4.87 to
4.90). Gelatin stock treated with lime shows greatest turbidity on the acid
side of the isoelectric point and, vice versa, those stocks treated with acid
possess isoelectric points in the region of />H 7 to 8.
Previous history. The temperature to which a gelatin has been pre-
viously heated will cause a variation in its viscosity. It may also change
its stiffening power. This heating may be due to heating during manufac-
ture or to heating for dissolving in the home. The latter is seldom long
enough to destroy the jelly strength to any appreciable extent. A gelatin
solution that has solidified and then is melted will form a gel in a shorter
time for the second or third gelation.
LITERATURE CITED AND REFERENCES 187
Agitation and foam formation. Bogue and Alexander both state that
agitation or stirring lessens the viscosity of gelatin solutions. This might
also affect the jelly strength. Gelatins are often beaten when they have
become thick but not firmly set. The beating incorporates air, forming a
foam, and the gelatin mixture increases in volume. Bogue states that the
ability for gelatin to form a foam is greatest at the isoelectric point. At
this point the gelatin particles have a strong tendency to adhere to each
other, and this favors foam formation. If the beating is done at the time
when the gelatin has set enough to be quite viscid, but has not become
brittle, so that the edges break apart, the volume may be increased two or
three times that of the original unbeaten gelatin. The lessening of firmness
may be partially due to agitation of the gelatin, but part is due to the
incorporation of air. The gelatin at this stage is elastic and stretches to
surround the air particles. The gelatin that is to toe beaten should have
the flavoring in larger quantity than for an unbeaten gelatin as the increase
in volume causes the flavor to seem less concentrated. If gelatin becomes
too firm before the beating is started the gelatin only breaks and air is not
incorporated. Whipped cream and beaten egg white are often folded into
unbeaten gelatin or into beaten gelatin.
LITERATURE CITED AND REFERENCES
Alexander, J. Glue and Gelatin. Chemical Catalog Co. (1923).
Alexander, J. Colloid Chemistry, Theoretical and Applied, by Selected Interna-
tional Contributors. Edited by Alexander. Chemical Catalog Co. (1926).
Bancroft, W. D. Applied Colloid Chemistry. McGraw-Hill Co. (1933).
Black, J. W. Opacity in Gelatine. Food Technology 1: 162 (1931-32).
Bogue, R, H. Chemistry and Technology of Gelatin and Glue. McGraw-Hill
Co. (1922).
Bogue, R. H. The Evaluation of Gelatin and Glue. Ind. Eng. Chem. 14: 435
(1922).
Bogue, R. H. The Theory and Application of Colloidal Behavior. International
Chemical Series. McGraw-Hill Co. (1924).
Bradford, S. C. The Sol-gel Transformation and the Properties of Jellies.
p. 751, Colloid Chemistry, edited by Alexander. Chemical Catalog Co.
(1926).
Carpenter, D. C., Dahlberg, A. C., and Hening, J. C. Grading Commercial
Gelatin and Its Use in the Manufacture of Ice Cream. I. Ind. Eng. Chem.
20: 397 (1928).
Clark, A. W., and Du Bois, L. Jelly Value of Gelatin and Glue. Ind. Eng.
Chem. 10: 707 (1918).
Clayton, W. Foods as Colloids Systems. Food 4: 195 (1935).
Dahlberg, A. C., Carpenter, D. C., and Hening, J. C. Grading of Commercial
Gelatin and Its Use in the Manufacture of Ice Cream. II. Ind. Eng. Chem.
20: 516 (1928).
Edwards, P. R. Opacity in Gelatines. Food Technology 1: 100 (1931-32).
Lloyd, D. J. On the Swelling of Gelatin in Hydrochloric Acid and Caustic Soda.
Biochemical J. 14: 147 (1920).
Lloyd, D. J. The Problem of Gel Structure, p. 777, Colloid Chemistry. Edited
by Alexander. Chemical Catalog Co. (1926).
188 GELATIN
Loeb, J. Proteins and the Theory of Colloidal Behavior. McGraw-Hill Co.
(1922).
Loeb, J. Crystalloidal and Colloidal Behavior of Protein. Chapter II. The
Theory and Application of Colloidal Behavior. Edited by Bogue. McGraw-
Hill Co. (1924).
Ostwald, Wo. An Introduction to Theoretical and Applied Colloid Chemistry.
Translation by Fischer. John Wiley & Sons (1922).
Ostwald, Wo., Wolski, P., and Kuhn, A. Practical Colloid Chemistry. Transla-
tion by I. N. Kuegelmass and T. Cleveland. Methuen & Co. London (1926).
Patten, H. E., and Johnson, A. J. The Effect of Hydrogen Ion Concentration
on the Liquefaction of Gelatin. J. Biol. Chem. 38: 179 (1919).
Rideal, S. Glue and Glue Testing. Scott, Greenwood & Son. London (1926).
Sheppard, S. E., and Elliott, F. A. The Reticulation of Gelatine. Ind. Eng.
Chem. 10: 727 (1918).
Sheppard, S. E., and Hudson, J. H. Pressed Foam Gelatin. Ind. Eng. Chem. 28:
422 (1936).
Sheppard, S. E., and Sweet, S. S. The Setting and Melting Points of Gelatins.
Ind. Eng. Chem. 13: 423 (1921).
Sheppard, S. E., Sweet, S. S., and Scott, J. R. The Jelly Strength of Gelatins
and Glues. Ind. Eng. Chem. 12: 1007 (1920).
Weiser, H. B. Jellies and Gelatinous Precipitates. Chapter XV. The Theory
and Application of Colloidal Behavior. Edited by Bogue. McGraw-Hill
Co. (1924).
GELATIN
Directions for cooling gelatin. The gelatin solutions should be put
to cool at the same temperature. Those from the same experiment should
be on the same shelf in the refrigerator, as the upper shelves have a higher
temperature than the lower ones. A cooling room is a splendid place to
put them while cooling. For class work when periods are short the setting
may be hastened by putting the containers in crushed ice. The ice should
be the same depth around all the containers. It is better to have all the
containers for one experiment in the same pan of ice for cooling. The
containers should be the same size, shape, and material, for if they are not
the same size the surface area for cooling will be greater for some than
for others. Enamel or aluminum are good materials for cooling gelatin
solutions. Crockery or china cools more slowly than metal.
The proportion of gelatin suggested in the following experiments, 3.5
grams for a cup of liquid, is not the best proportion for all gelatins.
With some brands or grades about 2 per cent or about 4.8 grams per cup
of liquid will be required for the best results. Find the best proportion
of gelatin for the brand that is being used and substitute that amount for
the amount given in the experiments. Use the same brand for all the
experiments except Experiment 30.
Record the time and temperature when the gelatin is mixed, \vhen it
begins to gel around the edges, and when set. If cooled in crushed ice
make a record of the temperature every 5 minutes and plot on graph paper.
Find the effect on the texture of the gelatin of standing 20 minutes at
GELATIN
189
room temperature. Most gelatins will need to stand at least 20 minutes
or longer for serving.
Experiment 29.
To determine the effect of dissolving gelatin by different methods on the
time required for setting and the temperature at which gelation occurs.
A. Hydrate 3.5 grams of gelatin with 30 cc. of cold water. Add 206.5 cc.
of boiling water. Stir until dissolved. Record the temperature when mixed and
the time when mixed. Set in crushed ice. Record time and temperature every
5 minutes or more often until set. Plot on graph paper.
B. Hydrate 3.5 grams of gelatin with 30 cc. of cold water. Let stand 5
minutes, then melt over hot water. The temperature of the hot water should
be 85 to 90 C. Stir the gelatin until melted, remove from above the hot water
and add gradually while stirring 206.5 cc. of cold water. Follow directions for
cooling under A.
C. Hydrate 3.5 grams of gelatin with 30 cc. of cold water for 5 minutes.
Stir while adding 60 cc. of boiling water. After gelatin is dissolved add 131.5
cc. of cold water. Follow directions for cooling under A. Compare the length
of time required for setting, the temperature at which setting occurs, and the
ease of dissolving by each method.
What proportion of an ounce is 3.5 grams? What proportion of an envelope
of gelatin? What is the measure in teaspoons? A total of 240 grams of liquid
and gelatin is used. What proportion of 240 grams is 15 cc. ? What percentage
is 3.5 grams?
Gelatin,
grams
Gelatin,
measure
Gelatin,
per cent
Time re-
quired to set
Temperature
when mixed
Temperature
when set
Results and conclusions.
Experiment 30.
To determine the stiffening power of different brands of gelatin.
Use as many different brands and kinds of gelatin as you can obtain. Use
plain gelatin. If acidulated gelatins are used they should be compared with
acidulated gelatins and not with plain ones. Notice the color and odor of each
gelatin solution. Use a total of 240 grams of gelatin and liquid. Compare the
length of time required to set and the firmness of the jellies. Do any of the
gelatins require too long a time to set to serve in a reasonable time? Are any
of the gelatins too firm?
1. Hydrate 3.5 grams of gelatin with 30 cc. of cold water. Dissolve by
warming over hot water. Add 176.5 cc. of cold water, 30 cc. of lemon juice,
and 50 grams of sugar. Follow directions under 29A for cooling.
2. Repeat 30,1, with as many different brands and grades of gelatin as have
been obtained.
190
GELATIN
Brand
of
gelatin
Gelatin,
per cent
Time
to set
Temper-
ature
when
mixed
Temper-
ature
when set
Texture
Color
Odor
but reduce the cold water to 176.5 cc. and increase lemon
Results and conclusions.
Experiment 31.
To determine the effect of distilled water, fruit juices, tomato, and vinegar
upon the stiffening power of gelatin and upon the time required for gelation.
Use a plain gelatin.
A. Water.
1. Use tap water. Hydrate 3.5 grams of gelatin with 30 cc. of cold water.
Follow directions for cooling under Experiment 29A.
2. Repeat Al, but use distilled water.
3. Repeat Al, but use softened water if obtainable.
B. Lemon juice.
1. Repeat Al, but reduce the cold water to 191.5 cc. and add 15 cc. of
lemon juice.
2. Repeat Al
juice to 30 cc.
3. Repeat Al
lemon juice.
4. Repeat Al
lemon juice.
C. Grape juice.
1. Repeat Bl, but substitute grape juice for the lemon juice.
2. Repeat B2, but substitute grape juice for the lemon juice.
3. Repeat B3, but substitute grape juice for the lemon juice.
4. Repeat B4, but substitute grape juice for the lemon juice.
D. Tomato juice.
1. Repeat Al, but substitute tomato juice for the cold water.
E. Vinegar.
1. Repeat B2, but substitute vinegar for the lemon juice.
2. Repeat B3, but substitute vinegar for the lemon juice.
but reduce the cold water to 146.5
and add 60
of
but reduce the cold water to 86.5 cc. and add 120 cc. of
Gelatin,
per cent
Time
required
to set
Temperature
when set
Proportion
of acid
added
Color
Texture
Results and conclusions.
GELATIN
191
Experiment 32.
To determine the effect of varying the percentage of gelatin upon the time
required for gelation and the stiffness of the gelatin.
1. Hydrate 3.5 grams of gelatin with 30 cc. of cold water. Dissolve by
warming over hot water. Add 176.5 cc. of cold water, 30 cc. of lemon juice,
and 50 grams of sugar.
2. Repeat 32,1, but increase the gelatin to 4.8 grams and reduce the cold
water to 174 cc. What is the percentage of gelatin used? Its measure?
3. Repeat 32,1, but increase the gelatin to 5.8 grams and reduce the cold
water to 172 cc. What is the percentage of gelatin used? Its measure?
4. Repeat 32,1, but increase the gelatin to 7.2 grams and decrease the cold
water to 171 cc.
5. Repeat 32,1, but decrease the gelatin to 2.4 grams and increase the cold
water to 192.5 cc.
Gelatin,
grams
Gelatin,
measure
Gelatin,
per cent
Time to
set
Temperature
when set
Texture
Results and conclusions.
Experiment 33.
To determine the effect of high temperatures upon the stiffening power of
gelatin.
A. Plain gelatin.
1. Hydrate 3.5 grams of gelatin with 30 cc. of cold water. Cover the bowl
to prevent the steam from condensing in the bowl and increasing the quantity
of liquid in the gelatin. If the quantity of liquid is increased, measure it and
decrease the cold water added accordingly. Place the covered bowl in a pressure
cooker and heat for 15 minutes at 15 pounds pressure. Take from the cooker
and add 176.5 cc. of cold water, 30 cc. of lemon juice, and 50 grams of sugar.
2. Repeat Al, but after hydrating add the lemon juice to the gelatin before
heating in the pressure cooker.
3. Hydrate 3.5 grams of gelatin in 30 cc. of cold water. Melt over hot water,
then add 176.5 cc. of cold water, 30 cc. of lemon juice, and 50 grams of sugar.
Does hydrolysis occur more rapidly when the gelatin contains an acid or
when plain? Does the one with the acid ever become stiff enough to serve?
B. Acidulated gelatin.
Repeat the directions under 33A, but use acidulated gelatin. Notice the
proportions given on the package for a cup of liquid and use the part of a
package needed for a cup of the gelatin solution. What is its weight and
measure? Make up 1 cup without heating in the cooker for a control. Compare
with A for time required to set and the texture of the gelatin.
192
GELATIN
Experiment 34.
To determine the effect of sugar upon the texture of a gelatin jelly.
1. Hydrate 3.5 grams of gelatin with 30 cc. of cold water. Dissolve by warm-
ing over hot water, then add 176.5 cc. of cold water, and 30 cc. of lemon juice.
2. Hydrate 3.5 grams of gelatin with 30 cc. of cold water. Dissolve by warm-
ing over hot water, then add 176.5 cc. of cold water, 30 cc. of lemon juice,
and 50 grams of sugar.
3. Hydrate 3.5 grams of gelatin with 30 cc. of cold water. Dissolve by warm-
ing over hot water, then add 176.5 cc. of cold water, 30 cc. of lemon juice,
and 100 grams of sugar. Compare the stiffness of the gelatins and the time
required to set. If desired the lemon juice may be omitted in Experiment 34
and the cold water increased to 206.5 cc. This will show the effect of the sugar
upon gelation and the stiffness of the jelly without the added lemon juice.
Sugar,
grams
Time to
set
Temperature
when set
Texture
Effect of sugar
on texture
Results and conclusions.
Experiment 35.
To determine the effect of fresh pineapple on the gelation property of
gelatin.
Hydrate 7 grams of gelatin with 60 cc. of cold water. Dissolve by warming
over hot water, then add 330 cc. of cold water, 60 cc. of lemon juice, and
100 grams of sugar. Divide into two equal portions.
1. To part one add 2 tablespoons of grated raw pineapple. Cool.
2. To part two add 2 tablespoons of cooked grated pineapple. Cool. Does
the gelatin containing the uncooked pineapple gel? Why? What is the effect of
cooking upon the pineapple? Results.
Experiment 36.
To determine the effect on the texture of gelatin of beating and the addi-
tion of whipped cream and beaten egg white.
Make up 4 cups of lemon jelly by hydrating 14 grams of gelatin with 120
cc. of cold water. Dissolve by warming over hot water, then add 720 cc. of
cold water, 120 cc. of lemon juice, and 200 grams of sugar. Divide into 4
equal parts. Metal quart cups are good to use for gelatins that are to be
beaten as the volume may be measured without removing from the container.
1. Cool.
2. Cool until it becomes thick enough to beat. Beat w r ith an egg beater until
the volume increases. Cool until firm. Obtain volume.
3. Repeat 36,2, but after beating fold in a stiffly beaten egg white. Cool
until firm. Obtain volume.
4. Repeat 36,2, but after beating fold in ^ cup of whipped cream. Cool
until firm. Obtain volume.
GELATIN
193
Compare for volume, flavor, texture, and number of servings obtained. Does
the volume increase or decrease when the whipped cream is folded into the
gelatin? Is the above proportion of lemon juice best for both a plain jelly and
a beaten jelly? What proportion of lemon juice and sugar would you suggest
for a plain jelly? For a beaten jelly?
Volume
Number of
servings
Texture
Flavor
Results and conclusions.
CHAPTER VII
MEAT
Grading and Stamping of Meat
Federal grading and stamping of meat was inaugurated in 1927. Davis
states that because the government grading is not influenced by season,
geographical location, or any other factor, the purchaser is assured, whether
by long distance or over-the-counter sales, of always securing, within cer-
tain narrow limits, the same quality of meat when buying a definite United
States grade. The service has grown until United States graded meat can
be purchased in many, though not all retail markets.
Classes of meat. Bovine animals are divided, because of characteristics
at different ages, into veal, calves, ^yearlings, and mature beef. Sometimes
baby beeves are given as a separate group between calves and yearlings.
The usual trade practise is to group baby beeves with yearlings. Sheep are
divided into lambs, yearlings, and mutton. The division into classes is based
on sex. Thus the classes of beef are steer-, heifer-, cow-, bull-, and stag-
beef. Carcasses from each class are further subdivided into grades. Grading
divides, in so far as possible, the carcasses, or subdivisions thereof, of the
uncooked meat into groups, the various grades indicating the relative
desirability of the meat for ultimate consumption, there being no exact
dividing line between one grade and that just higher or lower.
Basis for grading. The basis for grading is on what the grader calls
quality, conformation, and finish. Quality in so far as appearance can fore-
tell includes relative tenderness, juiciness, and palatability. By conforma-
tion is meant the form or shape, animals having broad, large, full muscles,
with relatively smaller proportion of bone, being graded highest. Finish
refers to the amount, quality, and color of fat within and around the
muscle. A few points considered in grading do not always affect the
palatability of the meat. For example, the fat of beef usually becomes more
yellow with age, so that whiter fat is graded higher than creamy or more
yellow fat. Yet in animals of the same age the deeper yellow color of the
fat indicates that the animal with more yellow fat had more carotene in its
feed. If conformation and finish both rated high, the meat from the animal
with yellow fat would undoubtedly be as palatable and also have more
nutritive value than meat from an animal with white fat. Grass-fed ani-
mals, because the meat is darker in color, may be graded lower, even when
all other points rate high.
194
MEAT
195
Courtesy Bureau of Agricultural Economics, Dept. Agriculture.
$ IG. 19. Showing the manner of branding for the hind and fore quarters of
United States graded beef. The small round marks are inspection brands.
196 MEAT
United States grading is a promiscuous service. The grading may
be done by federal graders or by the packers, but if by the packers only for
packer grades. If done by federal graders the meat is stamped with the
class of animal and the United States grade. See Fig. 19. The service is
paid for by the buyer of the meat. Grading is not a compulsory service
but a promiscuous one. Davis states the cost of grading varies in different
establishments in proportion to the number of carcasses graded and stamped.
But the cost is small, being less than 1/20 of a cent a pound. Hence, any-
extra cost to the consumer should be largely for the quality obtained rather
than the cost of stamping. Grading insures the purchaser of uniform
quality, and both buyer and purchaser use the same terminology for
specifications and qualifications. In Seattle and in some other cities, all
retail cuts must be plainly labeled with the United States grade.
Grades. In general classes of carcasses are divided into seven or six
United States grades, though pork because it is more uniform in quality
than beef or mutton has only four grades. Steer- and heifer-beef are divided
into seven grades, but cow-, bull-, and stag-beef are divided into six
grades, the top grade, Prime, being omitted. Lamb and mutton are divided
into six grades.
The seven United States beef grades are designated by both a name and
a number and follow: No. Al, Prime; No. 1, Choice; No. 2, Good; No. 3,
Medium; No. 4, Common; No. 5, Cutter; and No. 6, Low Cutter. The
grades for lamb and mutton are similar to those for beef, except that No. 5
is called Cull and there is no No. 6. The pork grades are No. 1, No. 2,
No. 3, and Cull.
The stamp indicating the grade is put on with a roller. The material
used for stamping is an edible, vegetable compound which often disappears
during cooking. Stamping starts at the shank, continues over the round,
the rump, the loin, along the back over the prime-rib beef cuts, and to the
neck. See Fig. 19. In beef another line is put over the shoulder. Thus the
stamp indicating grade occurs on all major retail cuts. Although, as has
been indicated, all the grades may be stamped, in actual practise the bulk
of the beef that has been graded and stamped has been the Prime, Choice,
and Good grades of steers and heifers. Some Choice cow-beef is stamped.
Only a small amount of steer- and heifer-beef below Good is graded and
practically no bull- or stag-beef is graded.
The proportion of classes to total beef, in percentage, for a 30-month
period, July 1, 1918, to Dec. 31, 1920, are given by Davis and Whalin as
follows: Steer, 49.94; bull and stag, 3.57; cow, 36.53; and heifer-beef,
14.96.
The approximate distribution of steer-beef by grades is given by Davis
and Whalin as follows: Prime, about 0.5; Choice, 4; Good, 22; Medium,
53; Common, 17; and Cutter and Low Cutter combined about 3.5 per cent.
Very little of the two lowest grades can be purchased on the retail
TRICHINOSIS 197
market, practically all of the meat, except that used for boneless cuts such
as tenderloin, being used in products like sausage.
Packer brands. Packers designate their better quality of meat by brand
names. If the United States grade is stamped on the meat the packer brand
is not used.
Federal Inspection of Meat
All meats shipped from one state to another are under federal surveil-
lance. This includes the meat produced by the larger establishments, about
two-thirds of that consumed. Each state and the cities usually have some
regulations concerning meats and supervision of local plants.
The purpose of inspection is to insure that the meat sold to the con-
sumer is from healthy animals, in sound condition at the time of slaughter.
The inspection stamp is round and is placed on each wholesale cut and
on all grades of meat. In Fig. 19, the four round stamps are inspection
stamps placed on what will be the wholesale cuts of round, rump, sirloin,
and short loin.
Inspection of carcasses and the supervision of making of meat products
safeguard the consumer. However, in one instance, inspection cannot
entirely safeguard the consumer. There is no accurate, quick method that
can be used in inspection that detects trichinae in trichinae-infected pork,
though federal supervision does insure that products to be consumed with-
out further cooking are so treated that no live trichinae are present. It
should be stated that only a small percentage of pork is infected with
trichinae.
Trichinosis. Trichinosis is contracted by eating uncooked, trichinae-
infected meat, usually pork. Any animal eating pork may contract the
disease, however, and cases have been reported in the medical literature
that were traced to the eating of raw, jerked bear meat.
It is assumed that anyone buying fresh pork chops, roasts, etc., will cook
the meat. But some people grind raw lean pork, season it, and use it in
sandwiches. Others in making homemade sausage taste the uncooked
product to see that the seasoning is satisfactory.
Ransom and Schwartz found that live trichinae are quickly destroyed by
heating the meat to 55C. They may be destroyed at 50C. if the meat is
held at this temperature for a sufficient time. Ransom found that trichinae
are destroyed by freezing, provided the frozen, infected meat is held at a
temperature not higher than 5F. for 10 days.
All lean pork, in plants under federal supervision, used with other meat,
or in pork products that are to be consumed without further cooking, must
be treated to make sure that any live trichinae that may be present are
destroyed. Such products include soft or fresh and dry summer sausages,
frankfurters and Vienna-style sausages, Italian and Westphalian-style hams,
198 MEAT
pork butts in casings, cured pork loins in or without casings, capicola, coppa,
cotto salami, and other products.
In general the methods used for destruction of trichinae are ( 1 ) freezing
and storage and (2) heating, or a combination of one or more of these
methods.
The freezing treatment is called refrigeration. The lean pork and pork
trimmings are frozen. The specifications, based on the work of Ransom and
allowing 10 extra days for a margin of safety, are that the frozen meat
must be stored for 20 days at a temperature not higher than 5F.
Heating is called processing. The specifications, based on the work of
Ransom and Schwartz and allowing a margin for safety, are that the meat
must be heated to 58.3C. (137F.). Some products may be heated to
only 128F. but must be held at this temperature, often in a smoke room,
for a specified number of hours.
Salt treatment is used for some products, but a large amount, 4.5 per
cent, of salt must be used and a dry cure employed. The meat must be
held in this salt cure for a period of 20 to 25 days at specified temperatures
and further specific procedures must be followed.
Definition of Meat and Flesh
The Food and Drug Administration in "The Service and Regulatory
Announcements of 1933" define meat and flesh as follows: "Meat is the
properly dressed flesh derived from cattle, from swine, from sheep or goats
sufficiently mature and in good health at the time of slaughter, but is
restricted to that part of the striated muscle which is skeletal or that which
is found in the tongue, in the diaphragm, in the heart, or in the esophagus,
and does not include that found in the lips, in the snout, or in the ears,
with or without the accompanying and overlying fat, and the portions of
bone, sinew, nerve, and blood vessels which normally accompany the flesh
and which may not have been separated from it in the process of dressing
it for sale.
"Flesh is any edible part of the striated muscle of an animal. The term
'animal' as herein used, indicates a mammal, a fowl, a fish, a crustacean,
a mollusk, or any other animal used as a source of food."
Muscles
A muscle is an organ made up of fibers held together by connective
tissue and surrounded by a sheath of heavier connective tissue. The fibers
are grouped parallel to each other in bundles called fasciculi. See Fig. 20.
Even the thinner sheets of connective tissue entering the bundle are shown
in some portions of the photograph. The connective tissue entering the
fasciculi is the endomysium. The size of the bundles or fasciculi varies in
different muscles and determines to a certain extent the grain of the meat.
TENDER AND LESS TENDER CUTS 199
The connective tissue surrounding the fasciculi, the perimysium, varies
in thickness, being quite perceptible to the eye in some muscles, as in the
outer muscle of prime ribs shown in Fig. 20. In some muscles it is scarcely
discernible. The connective tissue enclosing each muscle is known as the
epimysium or muscle sheath. The thicker, denser portions of the muscle
sheath are often little changed during cooking and constitute tough spots
in the meat.
FIG. 20. This photograph shows the bundles of muscle fibers, the fasciculi, and
the surrounding connective tissue, the perimysium. Even the connective tissue
entering the bundles of muscle fibers is shown in many places. This muscle is the
narrow muscle along the outer edge of a beef roast. The photograph was taken
after the meat was cooked. The muscle is pulled apart and pinned back. Enlarged
about three times.
The spaces between the muscles, the fasciculi, or the cells are referred to
as intermuscular, interfascicular, or intercellular; the area within the
muscle, the fasciculus, or cell is called intramuscular, intrafaspicular, or
intracellular.
Classes of muscles. Muscles are divided into two groups, the skeletal,
voluntary, or cross-striated and the smooth, plain, or long-striated. The
smooth muscles occur in the walls of the hollow viscera, i.e., the intestinal
tract, the arteries, veins, etc. Heart muscle is cross-striated but in many
of its characteristics it falls between the two groups, voluntary and invol-
untary. The skeletal and heart muscles compose the muscle designated as
flesh by the Food and Drug Administration.
Some muscles are exercised more than others. The muscles in the
body of an animal are not exercised or used equally. Thus, depending upon
200 MEAT
the extent to which the muscles have been used, "tender" and "less-tender"
cuts are obtained from the same animal. In general the less-tender cuts are
obtained from the neck and legs, the tender cuts along the back.
Fat
Fat may be deposited around and between each muscle, i.e., inter-
muscularly; between the fasciculi, interf ascicularly ; between the fibers,
intrafascicularly; or within the fiber, intracellularly. The nodular white
spaces between the fibers, Fig. 21, were occupied by fat cells, i.e., intra-
fascicular fat. The fat was removed in preparation of the section, but the
membrane between the fat cells still shows. Although fat deposited around
and within the muscle is not important in the contraction of the muscle,
that around the muscle, and particularly in roasts, bastes the roast during
cooking and thus affects the palatability.
Fat content. The fat content of the body, and hence of the muscles
and finally the "cuts" of meat, varies with the nutritive condition and age
of the animal. Well-nourished animals have more fat distributed over and
throughout the muscles. In general older animals tend to deposit more fat
within and around the muscle than young ones.
It is generally conceded that the presence of fat around and particularly
within the muscle increases the juiciness of the meat. Some water is de-
posited with the fat and this, combined with melted fat is probably
responsible for the apparent increased juiciness.
Some cuts contain more fat. Cuts coming from certain locations con-
tain relatively more fat than cuts from other parts of the body. Fat tends
to be deposited first subcutaneously and around the internal organs. In
general deposition of fat intermuscularly and intramuscularly comes later,
and last of all its deposit within the individual fibers. The deposition of
fat within the lean tissues is known as marbling, which undoubtedly in-
creases the palatability of the meat. But to secure marbled muscular tissues
a rather thick fat covering is essential (i.e., the portion of the cut lying
beneath the skin) and, because meat is eaten primarily for its lean content,
many housewives think this fat covering of the muscles is unnecessary. The
fat covering differs in thickness in various cuts so that no definite statement
can be made as to the most desirable thickness. But for a prime rib roast
most persons prefer a covering of about ^4 inch, some liking more and
others less. The fat covering can become so thick and heavy that it does
not materially increase the palatability and is wasteful.
Adipose tissue. Adipose tissue is largely made up of fat cells within
connective tissue. For human fatty tissue Burns gives the composition:
water 15 per cent, fat 82.5 per cent, and protein 2.5 per cent. Gortner
states that adipose tissue often contains as much as or more water than it
does fat.
MEAT
201
Courtesy of Fred J. Beard, Iowa State College
FIG. 21. Longitudinal section of muscle fibers of beef. The white nodular spaces
are fat cells. The pulling apart of the fibers in preparation is shown by the long,
narrow, white spaces. The burled looking part of the fibers is due to pulling of the
knife edge in cutting. The cross striations show plainly in the fibers to the left of
the fat cells. Magnification approximately x 200.
202 MEAT
Size of fat cells. The size of the fat cells varies with the nutritional
state of the animal. Hammond states that they may be 10 to 20/x, in a starved
animal, 50/x in one in ordinary condition, and up to 175/x in a very fat one.
The cells are smaller within the connective tissue and in the marbling fat
within the muscles and larger around the internal organs and sub-
cutaneously.
Connective Tissue
Hammond states, that there is evidence that the connective tissues go on
growing longer than other tissues in the body, and that maturity in them
is not reached so soon as in other tissues. This may be one explanation of
why meat from older animals is in general tougher than meat from younger
animals. Hammond says that with increased feeding fat is deposited in
the connective tissue.
Kinds of connective tissue. The connective tissue of meat is com-
posed of two kinds, the yellow and the white. The amount and kind vary
in meat from different animals and in different cuts from the same animal.
Burns states that the function of the tissue governs the form produced.
When binding power alone is required the white tissue is formed, but
when elasticity as well as strength is necessary, there the yellow tissue is
found. Tendons are composed almost entirely of the white, non-elastic
tissue; ligaments are principally the yellow tissue. Many muscles seem to
require both elastic and binding tissue, hence both are often found in the
connective tissue binding the fibers.
The yellow connective tissue is feebly but perfectly elastic and is found
in ligaments, in the connective tissue between the muscle fibers, in the
walls of the blood vessels, and in other parts of the body. The best example
of the yellow tissue is the ligamentum nuchae of the ox. It is the tough
yellow ligament found along the backbone, which is used in elevating the
head of the animal ; it is much thicker and heavier along the ribs and fore
quarter than along the loin.
The white connective tissue is non-elastic and is found in the connective
tissue between the muscle fibers and in the tendons, the tendon Achilles
being a good example.
Composition of connective tissue. The percentage of water in the
connective tissue of the young animal is higher than in the older animal.
Buerger and Gies have reported that the white connective tissue of the
calf contains about 68 per cent of water, whereas that of the ox has about
63 per cent. The solids of the connective tissue are made up of inorganic
and organic matter. Buerger and Gies have reported the following com-
position of the tendon Achilles of the ox; Vandergrift and Gies have
reported the composition of ligamentum nuchae of the ox.
The collagen and elastin content of connective tissue are of especial
ELASTIN
203
TABLE 24
COMPOSITION OF THE FRESH TISSUE OF ACHILLES TENDON AND THE FRESH
LlGAMENTUM NuCHAE OF THE Ox
Constituents
Tendon Achilles,
per cent
Ligamentum
nuchae, per cent
Water
62.870
57 570
Solids
37 130
42 430
Inorganic matter
470
470
S0 3
031
026
P 2 O 5
039
035
Cl
147
136
Organic matter
36 . 660
41 960
Fat (ether-soluble matter)
1 040
1 120
Albumin, globulin . . .
220
616
Mucoid
1 282
525
Elastin
1 633
31 670
Collagen (gelatin)
31 588
7 230
Extractives and undetermined
0.896
0.799
interest in meat cookery, for both are found in the connective tissue
between the muscle fibers, but heat and moisture affect the two differently.
Collagen. Table 24 shows that the white connective tissue contains
nearly 32 per cent of collagen and about 7 per cent of elastin. Collagen
in the presence of moisture and at high temperatures yields gelatin. Bogue
states that collagen is changed to gelatin more rapidly at the boiling
temperature of water, or at temperatures above boiling obtained by pres-
sure, and more slowly at temperatures below boiling. The gelatin is dis-
solved in the water or broth. If the meat is cooked long enough, the larger
part of the connective tissue is dissolved, so that the muscle fibers may fall
entirely apart. Sometimes in cooked meat only the outer portion of the
fibers is separated and the inner portion is still connected. The surface of
the meat reaches a high temperature before the interior of the meat, thus
the collagen of the connective tissue near the surface may be changed to
gelatin first.
Elastin. Vandergrift and Gies have reported the yellow connective
tissue as containing about 32 per cent of elastin and about 2 per cent of
collagen. The elastin is a very resistant, firm protein and is not changed
or affected by heat and moisture. In cooking, yellow connective tissue is
not softened. Consequently cuts of meat containing large amounts of
elastin in the connective tissue will be tough after cooking, whereas cuts
containing large amounts of collagen may have part or all of the collagen
changed to gelatin.
204
MEAT
TABLE 25
CONNECTIVE TISSUE PROTEINS IN MEAT (Mitchell, Zimmerman, and Hamilton)
No.
Description of sample
Total
nitrogen
in sample,
per cent
Collagen
nitrogen
in
percentage
of total N
Elastin
nitrogen
in
percentage
of total N
Collagen
and
elastin
nitrogen
in
percentage
of total N
15.
16.
1. Beef rib 3.19
4. Beef rib 3.35
5. Beef shank 3.42
6. Pork tenderloin 3 . 68
7. Chicken, compositebone-
less meat from 2-lb.
cockerels 3.63
Chicken, composite bone-
less meat from 2-lb.
pullets 3.48
11. Chicken, breast muscle
from 3-lb. cockerel ... 3 . 24
12. Chicken, thigh muscle
from 3-lb. cockerel 3.21
13. Chicken, breast muscle
from 3-lb. pullet 4.06
14. Chicken, thigh muscle
from 3-lb. pullet 3.23
Chicken, breast muscle
from 4-lb. cockerel
Chicken, thigh muscle
from 4-lb. cockerel . .
4.14
3.69
8.4
7.9
4.2
4.2
7.5
6.2
3.0
2.3
19.6
17.8
18.0
2.1
1.1
2.4
2.0
3.4
12.2
12.4
6.5
6.8
11.9
13.5
6.4
7.2
8.1
8.2
14.4
12.0
1.7
1.8
5.2
3.7
4.1
0.8
0.6
3.7
6.5
0.3
1.7
1.7
1.6
1.6
1.8
2.4
14
15
12.9
12.4
21.9
18.2
4.7
4.2
24.8
21.5
22.1
2.9
1.7
6.1
8.5
3.7
13.9
14.2
8.1
8.4
13.8
13.9
LESS TENDER CUTS HAVE MORE CONNECTIVE TISSUE 205
Less tender cuts have more connective tissue. Data given in Table
25 are from the earlier work of Mitchell et al., so that the percentage of
elastin given is too high, but the comparative amounts in different cuts are
shown.
In later work Mitchell and co-workers found that the percentage of
elastin in muscle is small, but in general the less tender contain a larger
proportion than the tender cuts.
From the experiments, results given in Table 26, Mitchell et al. find
no relation between the ordinary market grading of beef carcasses and the
connective-tissue content, the eye-muscle of ribs from the carcass of a
canner cow having no more collagen than that from a choice steer. The
results of their "investigation lend no support to the belief that the appear-
ance, texture, and firmness of beef lean give reliable information concern-
ing its tenderness." This suggests that other factors than the connective-
tissue content alone affect the tenderness of meat, for most persons would
prefer taking a chance on the eye-muscle of ribs from a choice steer being
more tender than that from a canner cow.
Pork contains little connective tissue. Mitchell et al. have found that all
the different cuts of pork contained more nearly the same percentage of
connective tissue than the different cuts of veal or beef.
TABLE 26
THE COLLAGEN AND ELASTIN CONTENT OF THE "RIBEYES" OF THE QTH, lOra,
AND HTH RIBS OF BEEVES OF DIFFERENT GRADE (Mitchell, Hamilton,
and Haines)
Dry
Fni-
Colla-
Elas-
Colla-
Elas-
Esti-
matter
r it
gen-
tin-
gen N
tin N
Carcass
grade
mated
age,
Sex
con-
tent,
con-
tent,
con-
tent,
con-
tent,
con-
tent,
in per
cent of
in per
cent of
years
per
per
cent
per
cent
per
per
total
total
cent
cent
cent
N
N
Choice
1
steer
25.82
3.59
2.50
1.08
0.004
5.4
0.02
Choice
2
steer
27.87
3.55
4.35
1.89
0.006
9.4
0.03
Good-f-
4
steer
29.07
3.25
7.78
1.19
0.011
6.5
0.06
Good
young
cow
25.16
3.42
2.99
1.16
0.001
6.1
0.005
Good
4
steer
29.48
3.30
7.14
.33
0.002
7.2
0.01
Good+
2
steer
26.08
3.57
3.54
.49
0.003
7.4
0.015
Medium+
1
heifer
23.82
3.34
0.97
.05
5.6
Medium+
cow
26.82
3.34
4.63
.59
0.002
8.5
0.01
Medium+
3-4
steer
26.83
3.36
5.18
.32
0.008
7.0
0.04
Medium
3-4
steer
26.12
3.40
3.62
.15
0.032
6.1
0.16
Common+
old
cow
25.22
3.46
2.92
.74
0.004
9.0
0.02
Canner
14-15
cow
26.62
3.56
3.51
0.92
0.008
4.6
0.04
206 MEAT
Connective tissue in fish. The connective tissue of fish is small in
amount and probably contains mostly collagen with little or no elastin, for
it is very easily disintegrated and easily dissolved by cooking, leaving the
muscle fibers separated.
The Muscle Fibers
Each fiber is elongated, cylindrical, and multi-nucleated. Howell states
its length does not exceed 36 mm. but the species is not stated. The average
length varies in different muscles in the same animal and in the same
muscles in different kinds of animals. Hammond says that the average
length of goat fibers is said to be greater than those of beef, and those of
beef greater than fibers in mutton. The average diameter also varies in
different muscles, in different species, and in the same animal with age.
Hammond found the average diameter of a particular muscle of Suffolk
ram at birth, at 5 months, and at 4 years to be 12.8/x, 40.3/m, and 54.1^,
respectively. It is commonly accepted that the number of fibers does not
increase after birth so that, in spite of increase in diameter with age, the
size of the muscle is largely determined by the number and length of the
fibers rather than their thickness.
Each fiber is enclosed in the sarcolemma, a thin, elastic membrane. A
thin, delicate band occurring regularly along the length of the fiber divides
the fiber into its structural units, the sarcomeres, a fiber being composed
of a succession of sarcomeres. A dark band shows in the middle of each
sarcomere, a lighter band on either side. The material between the fibrils is
known as the sarcoplasm and the relative amount of sarcoplasm varies in
muscles of different animals.
The contracting tissue, the fibrils, run the length of the fiber. The fibrils
consist of alternating light and dark segments which form the cross
striations of the fibers. See Figs. 21 and 22. The cross bands are supposed
to be of denser structure than the material between these bands. Fig. 22
shows the immense number of these cross striations. The cross striations
also show plainly in the fibers of Fig. 21.
All the material within the sarcolemma is known as the muscle plasma
and in the living muscle is in a semi-liquid state.
Effect of exercise and maturity upon fibers. Beard in his study of "Tough
and Tender Meat" states that "muscle fibers attain their maturity by use
and age. Development implies increase in size rather than maturity." Beard
made a microscopic study of different muscles of five different animals. The
animals selected for study were a heifer, a short-fed steer, a prime steer, an
old cow, and a veal calf. Some of his observations and conclusions are as
follows :
"Connective tissue seems more apparent in thinner fleshed beef.
"There was intracellular fat (fatty degeneration) in the fat steer.
THE MUSCLE FIBERS
207
"The fat steer had more intrafascicular, intercellular fat than any
animals studied.
"The inherent properties of the endomysium contribute to the toughness
of meat more than does the size of the fiber.
"The muscle fibers from the region of the toughest meat contain the
densest sarcoplasm, while fibers from the tenderest muscles contain the
lightest sarcoplasm.
"Intramuscular and particularly intrafascicular fat lessens the toughness
of meat.
Courtesy of Fred J. Beard, loiua State College
FIG. 22. Longitudinal section of muscle fibers of beef, showing cross striations.
Magnification approximately x 1400.
"Where only a small amount of intramuscular fat is found it is almost
always interfascicular. As the interfascicular fat increases in amount
intrafascicular fat appears which is first intercellular and in case of exces-
sive adiposity intracellular also."
Beard states that "while those muscles which are brought most into
activity and those performing the greatest amount of work may not possess
a larger fiber than those muscles which are less active, the more active
muscles do have a thicker perimysium and apparently more substance in
the fiber, as manifested in the staining characters of the sections."
Toughness of meat. Since meat is composed of muscle fibers and con-
nective tissue, toughness of meat must be due to either of these, or to both.
Toughness of connective tissue depends upon the proportion of elastin
and collagen ; upon the thickness or density of the tissue, which is brought
208
MEAT
about by use and activity; and possibly upon age, for it is common knowl-
edge that meat from old animals and fowls, whether domestic or wild,
is tougher than that from young animals. Toughness of the muscle fiber
depends upon the development and the density of the fiber due to activity,
and possibly to changes brought about by age.
The deposition of fat, either intramuscularly, intrafascicularly, or
intracellularly, tends to lessen the toughness. This is shown by the results
of mechanical tests with the dynamometer, which are given in Table 27.
The muscle used for these tests was the "eye" of beef or the longissimus
dorsi. The judges, as shown by scores, agreed w r ith the mechanical tests, the
roasts from the fattened animals being judged more tender than the roasts
from the lean animals. The possibility of toughness due to power to bind
water, which may be influenced by the reaction and salt content of the
fibers, thereby affecting the turgidity of the fibers, and the possibility of
toughening the fibers by heat coagulation are still to be considered.
TABLE 27
RESULTS OF TENDERNESS TEST WITH DYNAMOMETER ON FRESH BEEF
(Helser, Nelson, Lowe, and Helser)
Calves
Yearlings
Two-year-olds
Per-
Per-
Per-
cent-
cent-
cent-
age de-
age de-
age de-
crease
crease
crease
Feed-
ers
Fat-
tened
in
pounds
Feed-
ers
Fat-
tened
in
pounds
Feed-
ers
Fat-
tened
in
pounds
re-
re-
re-
quired
quired
quired
to
to
to
shear
shear
shear
meat
meat
meat
Pounds pull
required to
shear the
meat
39.50
32.37
18.05
35.41
24.75
30.10
36.78
28.62
22.19
Constituents of the Muscle Fibers
The muscle fibers contain several constituents, and these are grouped
as follows by Howell : "(1) Inorganic salts. (2) Ferments. (3) Pigments.
(4) Non-nitrogenous extractives (lactic acid, etc.). (5) Nitrogenous
PIGMENTS AND HEMOGLOBIN 209
extractives (creatine, urea, etc.). (6) Carbohydrates and fats. (7)
Proteins."
Inorganic salts. In meat cookery the inorganic salt most noticeable
from the standpoint of flavor is sodium chloride or common salt. The
juice from meat that has had no salt added before or during cooking
tastes salty. This is due to the sodium chloride of the body fluids, which
contain about 0.85 per cent. Care should be taken in adding salt to meat,
or the salt added in cooking plus that of the juices will result in an excess
of salt in the drippings and in gravy made from them. The muscle fibers do
not taste as salty as the juices, particularly if a large portion of the fluid
has been lost in cooking. The tissues do not contain as high a percentage
of sodium chloride as the fluids of the body.
The inorganic salts are found in a complex salt equilibrium in meat.
The ferments. Several different kinds of enzymes are found in muscle
tissue. The proteolytic, amylolytic, and lipolytic enzymes act on proteins,
carbohydrates, and fats, respectively.
Pigments and hemoglobin. When animals are slaughtered for food
the blood is drained from the body. However, some blood clings to walls
of the capillaries in the tissues. This blood together with the muscle pig-
ments gives to meat its pink or red color.
The hemoglobin of the red corpuscles is the pigment giving blood its
purplish-red color. The combination of hemoglobin with oxygen forms
oxyhemoglobin, which is a bright scarlet. Meat is a darker bluish-red when
first cut, but if the cut surface remains exposed to the air it becomes a
brighter red color. When hemoglobin and oxyhemoglobin are acted upon
by enzymes, acids, alkalies, or heat, various decomposition products are
formed. Hematin is one of the decomposition products formed by heat.
The coagulating temperature of oxyhemoglobin is around 64C. Thus
when meat is cooked to temperatures higher than this the production of
hematin brings about the brown or gray color of well-done meats. Dilute
acids or alkalies may also produce hematin from hemoglobin.
Muscle pigments. The red pigments of muscles resemble the hemoglobin
of the blood. These pigments are sometimes designated as chromatin sub-
stances. Whipple and Robscheit-Robbins call them muscle hemoglobin, and
they have reported that the properties of the muscle hemoglobin are prac-
tically the same as or identical with those of blood hemoglobin. Whipple
has found the content of muscle hemoglobin higher in active hunting dogs
than in inactive house dogs. He states that under different conditions the
muscles may contain from 10 to 80 grams of muscle hemoglobin for each
100 grams of blood hemoglobin.
Skeletal muscles vary in color in the same animal and in different species.
Sometimes the pigmentation varies in the same species but with different
types or breeds. Dairy cattle have darker-colored muscles than the beef
types. The color of the muscle of the young animal is often lighter than
that of the same muscle from an older animal. Veal is lighter in color
210 MEAT
than beef, and the leg muscles of broilers are lighter than those of mature
fowls. Different muscles of the rabbit vary in color from a very light pink
to a deep red. The different muscles of pork also vary in color. In general
the muscles of the lower animals are not pigmented, with the exception
of the heart muscle. The muscles of fish are white or light in color, but
the muscles of nearly all mammals are red. Needham states that "red pig-
mentation seems to occur in muscles from which the most persistent and
prolonged activity is required." Earlier investigators have also suggested
that in general pigmentation occurs in muscles used most frequently.
Effect of ripening upon meat pigments. Meat that has been ripened 40
to 60 days is usually a deeper gray in color, when cooked, than unripened
meat from the same animal, provided the cooking conditions are the same.
The darker color may be due to the action of enzymes and acid upon the
hemoglobin, so that more hemoglobin is broken down to produce hematin
at lower cooking temperatures, or it may be due to other factors.
Non-nitrogenous extractives. Lactic acid is always present in muscle
tissue. The amount is small while the muscle is at rest and increases during
and after exercise. After death the percentage of lactic acid in the muscle
increases.
Nitrogenous extractives. Muscle tissue contains end products of
protein metabolism. These are removed as they accumulate during life
from the tissues by the body fluids and are excreted through the kidneys.
Creatine and creatinine are found in the muscles and to a lesser extent
in the blood. Uric acid and other nitrogenous extractives are also found in
the muscles. They are of interest in meat cookery, because they are the
source of part of the distinctive flavor of meat, and stimulate the flow of
gastric juice.
Carbohydrates and fats. The carbohydrate found in the muscle tissue
is glycogen.
Burns states "the fat content of the cell is unique. Every cell has a
fairly constant content of lipide, although when stained by the usual
methods to demonstrate fat, no evidence is given of such a content. This
masked fat is only made visible when the cell is diseased or disintegrated."
The proteins of the muscle fibers. The proteins of the muscles are
composed largely of two types : ( 1 ) the structural proteins, which consist
largely of collagen aiid elastin and (2) the protoplasmic proteins, variously
called myosinogen, myogen, myosin, and myoglobulin. The two types of
proteins behave differently when heated, the effect of heat on the structural
or connective tissue proteins having been considered. The proteins of the
plasma are soluble in certain concentrations of salt solutions, such as
sodium chloride, sodium sulfate, magnesium sulfate, ammonium sulfate,
sodium phosphate, and other salts. Hence, they are often referred to as
the soluble proteins.
The entity of the meat proteins is in the same status as that of flour
POST-MORTEM CHANGES IN MEAT 211
and other food proteins. (See proteins of flour, Chapter XL) They may
or may not be a mixture of proteins having similar properties.
The soluble muscle proteins are most commonly designated as myosin
and myogen. They are classified as globulins, the myosin being completely
precipitated and the myogen partially precipitated by saturated magnesium
sulfate. However, complete information about these proteins is lacking.
Moran quotes Muralt as suggesting that the fibrils are composed of a
firmer material (myosin) surrounded by the more liquid or gel-like
myogen (sarcoplasm). The evidence for this was based on X-ray studies,
but is not generally accepted. Since myogen is doubly refractive, this is
almost conclusive proof that it occupies the light bands in the muscle fibers.
Characteristics of proteins. One of the outstanding characteristics is
the extent to which solubility is affected by small changes in salt concen-
trations. Smith has reported that exhaustive extraction with any given
salt yields only a fraction of the total protein. The highest yield, about
90 per cent, was obtained with 1.87 M NH 4 C1, followed by 1.65 M
LiCl, and a still lower percentage with the other salts tried. Howe found
that the total globulins (myosin and myogen) compose about one-third of
the total protein of the muscle, and that the insoluble protein composes
approximately one-half of the total protein of the muscles of the cow,
calf, and rabbit. In addition to variation with concentration, with the
number of extractions, and with different salts, the solubility varies with
pH. In general the proteins are less soluble at the isoelectric point.
The plasma proteins undergo denaturation by heat, acids, and surface
orientation. That the lactate ion affects the extent of denaturation and
the resulting density of myosin and albumen has been mentioned in
Chapter I. Still greater changes are brought about by heat when the meat
is cooked. In meat not only myosin and myogen may be found, but also
denatured myosin and denatured myogen. In cooked meats these proteins
may be entirely denatured.
Isoelectric point of muscle proteins. Smith gives the isoelectric point
of myosin as />H 5.0-5.3 and that of myogen as />H 6.3. Burns has given the
isoelectric point of myosin at pH 3.9 and that for the myoproteins at />H
4.5 and 5.
Post-Mortem Changes in Meat
Immediately after slaughter, changes occur in the muscle of an animal.
These changes, like the changes in milk and eggs, can be retarded by
method of handling and storage. They are brought about by enzymes and
microorganisms, and by chemical and physical means which alter the struc-
ture and chemical composition of the meat.
Muscle in the living animal is (1) pliant, soft, gel-like, yet somewhat
viscous. After slaughter the muscles pass from this state into a stiff or
rigid one (2) known as rigor mortis, or muscle rigor. After some time
212 MEAT
the muscles again become pliant. This stage (3) is known as the passing
of rigor. With longer storage enzymes and chemical means bring about
(4) more extensive changes which produce ripened meat. With bacterial
action and still more extensive changes (5) incipient putrefaction occurs.
The passage from one stage to another is gradual with no definite dividing
zone and is accelerated at higher temperatures and retarded at lower ones.
Meat may be cooked during any of these stages and heat denaturation
causes characteristic changes which are part of the post-mortem changes.
Means of retarding these changes will be considered before these changes
are discussed.
Meat cooked before the onset of rigor is said to be tender. But rigor
develops quickly so that this period is short. Concerning the question of
tenderness of meat before the onset of rigor, Dr. Trowbridge, who has
had many years of experience in meat work, wrote the author, "I doubt if
freshly killed meat is ever as tender as the same meat ripened."
Preservation of meat. Freezing. Meat may be frozen and then
stored at temperatures of 10 to 15F. In this way the post-mortem
changes are nearly inhibited.
Curing. Common salt is the basis of all cures or pickles. Although many
modifications are used, the methods may be divided into two classes, brine
and dry-salt cures. Salt not only preserves but tends to dry the meat. Sugar
may he added for flavor. Sugar also tends to keep the muscles softer than
when salt is used alcne and thus tends to increase the tenderness. When
sugar is added to the brine, the process is known as "sugar cure" or "sweet
pickle." Saltpeter (potassium nitrate) or Chili saltpeter (sodium nitrate)
or the nitrite salts of potassium and sodium may be used in cured meat.
The red color of cured meat is due to the action of nitrite on the hemo-
globin of the muscle. If only nitrate salts are used in the brine, they are
reduced to nitrite by bacterial action.
Cured meat may be smoked and partially dried on the surface. Actual
smoke and not chemical treatment to produce a smoke flavor must be used
in establishments under federal inspection.
Ham, bacon, and salt pork are probably the best known of cured pork
products. The loins when cured are often known as Canadian bacon.
Dried or chipped beef and corned beef are among the more familiar
cured-beef products. Beef cured in a brine is known as corned beef. Beef
cuts most often cured are the plates, flanks, and rumps, though from the
lower grades the chucks and rounds are often used. Dried beef is cured in
a sweet pickle, then dried and smoked. Usually the rounds and sometimes
the shoulder clods are used for dried beef.
Cold storage. The passing of rigor, ripening, and development of
putrefaction are delayed by quickly chilling the dressed meat and keeping
it at a low temperature just above the freezing point of meat. Moran states
that if the dressed meat is chilled slowly more protein is denatured than if
it is chilled quickly, and, because bacteria attack denaturated protein more
STORAGE OF MEAT IN THE HOME 213
rapidly than native protein, quick chilling is one means of increasing the
storage life of meat.
Chemically conditioned cold. Moran states that with temperature con-
trol alone the storage life of chilled beef is about 35 to 40 days. If, in
addition to low temperature control, what is sometimes known as "chem-
ically conditioned cold," i.e., 10 per cent of carbon dioxide, is used in the
storage atmosphere, the storage life of the meat may be extended to 60 or 70
days. The carbon dioxide retards or checks bacterial growth but if too
much is used with red meats such as beef and mutton, the surface of the
meat turns dark. This is because of the decreased amount of oxygen ob-
tained by the meat when carbon dioxide is increased. For fish a higher
percentage of carbon dioxide can be used. Stansby and Griffith have re-
ported that haddock packed in ice and plus an atmosphere of 15 to 40 per
cent of carbon dioxide have their storage life doubled over that when
packed in ice alone.
Contamination with bacteria and storage life. Another factor affecting
the storage life of meat is the initial contamination with bacteria. But with
care the initial contamination should be small. Other things being equal,
the smaller the initial load of bacteria the longer the storage life of the
meat. Spoilage by bacteria, yeasts, and molds is largely surface, and in
general does not extend to a greater depth than ^ to ^ inch. Hoagland,
McBryde, and Powick in their investigations of changes in beef during
cold storage above freezing found that "bacteria and molds grow on the
surface of cold storage carcasses but do not penetrate to any great depth
(less than 1 inch in 177 days)."
Microorganisms may enter the meat by penetration from the surface,
which is a slow process, and by following the cavities in meat, that is, the
blood and lymph vessels.
Empey found that bacteria grow and develop very slowly on meat during
rigor, as a />H of approximately 5.3 to 5.6 is not a desirable one for their
growth. Stansby and Griffith also found that bacteria do not develop rapidly
on fish during rigor.
Humidity. Mueller and Richardson have reported that dry air as well
as the low temperature is a factor in preventing bacterial growth. Hoag-
land, McBryde, and Powick found that in a cooler with low humidity the
growth of mold on the surface of the meat at 177 days was no greater than
in a cooler with higher humidity at 53 days.
Storage of meat in the home. Proper storage of meat in the home
is often a problem. Halves and quarters of dressed animals have a natural
protective skin covering. But when wholesale cuts are divided into smaller
parts, the surface area for contamination and the contamination both in-
crease from these cut surfaces coming in contact with meat blocks, hands,
wrapping paper, and kitchen and refrigerator utensils. In general, unless
frozen, meat should not be stored long in the home. Low temperatures and
214 MEAT
dry circulating air increase the storage life of meat. Burnett found roasts
keep best, steaks and chops next, and ground meat most poorly.
Rigor. During rigor meat is less tender than after the passage of rigor,
so that rigor is of interest in meat cookery.
Cause. The exact cause for the development of rigor is not known.
Hardy has suggested that two reversible reactions occurring in living
muscle, namely, glycogen ^ lactic acid and phosphagen ^ phosphoric acid
and creatine, are no longer reversible and after death proceed in one direc-
tion with the accumulation of lactic acid and creatine in the tissues.
Lactic acid has some role in the development of rigor, as rigor is usually
accompanied by or preceded by increase in lactic acid. But, Moran states,
under certain conditions, i.e., if an animal has been treated with insulin or
iodoacetic, rigor develops without the production of lactic acid. He also
adds that there are a number of chemical reactions which take place at
death that have not been defined and among them will be found the cause
or stimulus leading to the changes in the state of the proteins.
Tune of onset of rigor. At ordinary temperatures rigor is usually com-
plete in 10 to 12 hours. Rigor is supposed to develop more slowly at lower
and more rapidly at higher temperatures. But Smith found the effect of
temperature on the rate of onset of rigor to be variable.
Only skeletal muscles develop rigor. The proportion of soluble protein
is sometimes given as an explanation of why some muscles develop a greater
degree of rigor than others. Skeletal muscles contain a higher percentage of
soluble proteins than smooth muscles. The carcass of the pig generally does
not develop rigor, but occasionally one does. It is therefore interesting
to surmise whether this is due to a small proportion of soluble protein or
to other causes.
If there is more lactic acid than usual in the muscle of the animal when
killed, as happens when an animal is hunted or a chicken is chased before
killing, rigor sets in more quickly. Benson has reported that rigor sets in
more rapidly in fatigued fish muscle (trawl-caught) than in the muscle of
fish taken from a pen.
Changes occurring during rigor. In addition to the development of
turgidity, other changes occur simultaneously, for enzyme action does not
cease at the time of slaughter. There is evolution of heat known as the
heat of rigor. The glycogen practically disappears from the tissues and
this glycogen loss parallels the lactic acid increase. Moran states that for
mammalian muscle the lactic acid reaches a value of approximately 0.8 per
cent. The pH of the muscle falls from pH 7.2 or 7.4 to about />H 5.6 or
5.8, sometimes as low as pH 5.3. Because of various factors, such as
amount of glycogen to form lactic acid, the pH reached during rigor varies
somewhat.
It had previously been found without exception that the amount of
soluble protein is decreased during rigor; but Smith found no change in
solubility of the proteins in his investigation.
RIPENED MEAT 215
Passing of rigor from muscles. After a lapse of time rigor passes off.
The length of time varies with the speed with which rigor developed, with
different conditions and temperatures of storage, and with different animals.
It may require 5 to 6 days or longer at refrigeration temperature and a
shorter period at higher temperatures. It passes more rapidly from a carcass
in which rigor develops early. With the passing of rigor the muscles be-
come more soft and flexible. One observation that the author's family often
made was that chickens killed and stored before cooking over night in the
cellar were more tender than chickens cooked and eaten the same day they
were killed. The temperature of the cellar was higher than that of a
refrigerator, and the chickens were often chased before killing; these fac-
tors probably affected the time required for the passing of rigor.
The greatest physical change with passing of rigor is the increasing
tenderness of the meat.
Ripened meat. Noticeable changes that characterize ripened meat,
meat from which rigor has passed and which has stood some time, are
increased tenderness, change in flavor, and increased ease with which juice
may be pressed from the meat. The last is probably related to the increased
juiciness of the cooked, ripened meat.
Emmett and Grindley have reviewed the literature on changes in meat
during storage. The report of the work of Grassman is from their summary.
In experiments reported by Hoagland et al., for beef stored just above
the freezing point of the meat from 17 to 177 days, it is interesting to note
that all judges agreed that the flavor and tenderness of the meat are im-
proved with 15 to 30 days of storage. With storage for 45 days and longer,
they speak of an "old," "gamey," and "off" flavor. From the comments
one is led to believe that they like the meat stored for 56 days better than
that stored for 45 days. This was probably due to differences in the char-
acter of the quarters of beef from different animals. With longer storage
the flavor was not palatable, "old" and "off" being used to describe the
flavor developed.
Grassman has reported ripened meat as being more juicy, of better flavor,
and more tender than unripened meat. He adds that ripening meat to the
extent preferred by the English for roasting is not good for boiling, as it
imparts a disagreeable flavor to the broth.
Whether one prefers the flavor of ripened meat or that of fresh meat
is largely a matter of personal choice. It is hard to describe the flavor of
ripened meat, probably because there are no descriptive terms which convey
the same meaning to different people. Ripened meat is more acid, is richer
in flavor, and has more of a high or game flavor. Ripening may also
improve the flavor of the fat of the beef. The fat from some animals
develops a better flavor with ripening than that of other animals. When
it is improved, the flavor of the fat is more agreeable and more mellow.
However, the kind of feed the animal has received, as well as the age, sex,
216 MEAT
breed of animal, and the amount of fat may influence the flavor of the
meat and the fat.
Length of tune required for ripening. The length of time required for
ripening varies according to the degree of ripened flavor desired, and the
temperature at which the meat is stored. As the temperature is elevated the
time for ripening is shortened. At temperatures a little above the freezing
point of meat, 20 to 40 days seems to give the optimum flavor. Longer
than 40 days gives too high a flavor for most persons. Helser says, "When
ripened meat is properly trimmed and prepared there will be no mold flavor
at all, but you will have a rich, juicy, tender, and \vell-flavored piece of
meat. One trial will convince anyone."
Finished carcasses are best for ripening. Helser states that well-finished
carcasses are best suited for ripening purposes. Meat from carcasses of
animals that contain little fat "will get sticky, mold, and will have to be
trimmed heavily to avoid the moldy flavor." The layer of fat on the outside
of the prime beef and the greater quantity of fat in the muscle fibers pre-
vent the putrefactive bacteria from developing. Ripened meat develops a
growth of mold on the surface of the meat that must be removed before
cooking. Helser states: "The degree of ripeness is judged largely by the
length of the 'whiskers,' as the mold is sometimes called."
Changes in cooked beef due to ripening. Helser, Nelson, and Lowe have
found that roasts from the same animal, refrigerated under the same con-
ditions, show several distinct changes in cooking from that of fresh beef.
All the roasts were cooked at the same oven temperature and to the same
interior temperature. Roasts cooked after 10, 20, 40, and 60 days of storage
show a progressively gray color in the interior of the cooked roasts. Roasts
cooked to an inner temperature of 57 C. and cooked on the fifth, seventh,
and tenth days of storage were a bright red color ; w T hereas those ripened
60 days have only a little red or rose color. Roasts from calves are less red
and more gray in color than roasts from older animals.
Roasts from ripened beef brown more readily and this is true for both
the fat and lean than unripened roasts from the same animal, cooked
under the same conditions. In these experiments the results of scores for
palatability indicate that "in order to produce beef for roasts having the
most desirable beef flavor, steers should be at least 20 months old, and
preferably 30."
After the passing of rigor the roasts are more tender and become in-
creasingly tender with length of storage. Although the tenderness of the
meat increases with storage, the increase after 20 days of storage is prob-
ably not great enough to pay for the increased cost and trouble of storing.
With longer storage the roasts are more juicy. Also with ripening the
quantity of juice collecting in the platter when the roast is carved is de-
cidedly greater than for roasts cooked after 10 days or less than 10 days
of storage.
The flavor of the beef improved with ripening, and the maximum
CHANGES OCCURRING IN MEAT 217
development of flavor, under the refrigeration conditions used, came with
20 to 40 days of storage. For the connoisseur of flavor, this improved flavor
is decidedly worth the cost of storage.
Incipient putrefaction. Much discussion has occurred concerning the
presence of bacteria within muscle. Moran states that in freshly killed
muscle there is usually a low bacterial count. Hoagland, McBryde, and
Powick found that certain bacteria may normally be present in some
carcasses of beef, but they possessed no pathological significance and did
not multiply in proper cold-storage conditions. At low-storage tempera-
tures, spoilage by bacteria is most prevalent at the surface of the meat.
As has been indicated, growth is slow during rigor, for the acidity of the
meat does not favor the development of microorganisms. But with in-
creased storage of meat, the acidity of the meat is lessened or the alkalinity
increases and ammonia is liberated.
Of the different tests proposed for the detection of incipient putrefaction,
Baker believes that the determination of ammonical nitrogen has been the
most useful and the presence of 0.02-0.025 per cent indicates the beginning
of putrefaction. Thus Baker suggests that, when the pH has risen to pH
6.2 the meat has undergone deterioration.
Changes occurring in meat during storage. Changes due to
enzymes. The lipolytic, amylolytic, and proteolytic enzymes act on fats,
carbohydrates, and proteins, respectively. During life, these and other
enzymes are concerned with the metabolic processes of the body.
Enzyme changes are usually brought about more rapidly with higher
temperatures. At very low temperatures the action may be very slow and
different from that at higher temperatures owing to differenes in activity
of different enzymes at different temperatures. Hoagland, McBryde, and
Powick have reported that the external fat and kidney fat in beef stored
just above the freezing point of the meat showed increased fatty acid con-
tent and a corresponding deterioration of these fats. They found less
change in the intramuscular fat, as it was protected from bacterial action,
and changes in it were due to lipase enzymes. Oxidative changes in fats
are of course greater in the surface fat. The surface fat in ripened meat
often shows greater changes in flavor than interior fat.
Amylolytic enzymes bring about the change of glycogen to lactic acid.
These changes occur rather early in storage.
Proteolytic enzymes bring about changes of the proteins to amino acids,
thus increasing the amino nitrogen, or the non-protein nitrogen, or the
soluble nitrogen products of the meat. Hoagland, McBryde, and Powick
found that, in quarters of beef stored 14 to 177 days, the increase in amino
nitrogen amounted to 3 to 7 per cent of the total nitrogen of the beef.
Autolytic changes in beef at 37.C. Hoagland, McBryde, and Powick
stored pieces of beef free from bacteria in sterile containers at a tempera-
ture of 37 C. for periods of 7 to 100 days. Considerable juice exuded from
the pieces of meat, which turned brown in color. The beef was also brown
218 MEAT
on the surface for about ^ inch in depth, except where it touched the
container, and this was bright pink in color. Hoagland has reported that
this deep pink to a purplish-red color is due to hematoporphyrin. Its forma-
tion is attributed to enzymes. The meat retained its original form; the
sample stored 100 days was somewhat more tender than the one stored
7 days. The changes in the meat that could be detected by the senses of
sight, smell, and taste they called organoleptic changes. The odor changed
with increasing age. This change they describe as "rather old but not
unpleasant." The broiled 103-day sample of meat "is quite tender and has
an old, highly acid, and rather disagreeable flavor, which persists in the
mouth after eating; the meat is not entirely objectionable but is not
appetizing." In ordinary storage conditions meat cannot be kept free from
bacteria and is not stored at such a high temperature.
Chemical changes. In storage of meat the changes due to different
factors such as bacteria, enzymes, etc., are brought about simultaneously.
The chemical changes are the changes in the percentage of the different
constituents of the meat, however these may be brought about. Stored meat
usually loses weight by reason of moisture loss. The acidity increases.
Emmett and Grindley found that beef refrigerated 22 days compared
with meat from the same animal refrigerated 2 days at 33 to 35F., "(I)
had lost no water, (2) that the percentage of water soluble solids, the
soluble, insoluble and total protein, the non-coagulable protein, the nitrog-
enous and total organic extractives, the forms of ash, the total nitrogen
and the total phosphorus all remained practically unchanged. (3) That
the only consistent real changes were a distinct increase in the total soluble
and the soluble inorganic phosphorus, being 8.0 and 17.9 per cent respec-
tively, and a decrease of 8.3 per cent in the non-nitrogenous organic
extractives. (4) The nutritive value of the meat was unaltered." After
refrigeration for 43 days the chemical changes in the meat were greater
in number than those for the 22-day sample. When allowance was made
for the moisture loss they found a definite increase in the soluble dry
substance, the nitrogenous, non-nitrogenous, and total organic extractives,
the total soluble nitrogen, and the soluble inorganic phosphorus. There was
a slight increase in the soluble coagulable and total soluble protein nitrogen
and in the insoluble and total nitrogen.
They found the cooked meats from the 43-day refrigerated sample higher
in water content, therefore juicier, than the 6-day refrigerated sample.
From comparisons of other losses that occurred in the cooked 43-day
sample they concluded that it was as nutritious as that from the cooked
6-day refrigerated meat.
Changes in Cooked Meat and the Cooking of Meat
Meat is cooked to sterilize it and for most persons to make it more
palatable. It should be cooked in such a way as to increase its tenderness
JUICINESS 219
if it is a tough cut, and to keep it tender if it is a tender cut. It is desirable
in cooking meat to have maximum tenderness of both fibers and connective
tissue, so that the meat carves well and cuts easily. Meat cooked so long,
or at such a high temperature that the connective tissue is dissolved, is not
attractive and the fibers are tough and stringy. As a general rule, it should
be cooked in such a way as to retain its nutritive value, i.e., to prevent
cooking losses to as great an extent as possible, either dripping losses or
destruction of some food constituents by heat. When the drippings are
used in gravy or other ways this loss is not a serious one.
The flavor and the tenderness of the cooked meat depend to a great
degree upon the quality of the meat before cooking, for cooking cannot
make a well-flavored piece of meat from one of poor quality and flavor,
nor does it always produce a tender piece of meat. However, the method
and length of time of cooking may and often do spoil a good piece of meat,
yet the method of cooking may improve a poor piece of meat.
Browning and thoroughly cooking meat develop a different flavor, just
as cooking cabbage a long time develops a characteristic flavor. Many per-
sons prefer the development of this flavor.
Coagulation of proteins. The heat renders the soluble proteins of
meat insoluble, the extent of denaturation depending on the stage of
cookery or temperature reached, the time held at this temperature, the />H
of the meat, its salt content, its degree of ripeness, and probably other
factors. The higher the temperature reached and the longer the meat is
held at this temperature, the greater the denaturation. The relation of />H
to denaturation has been considered in Chapter I. With increased denatura-
tion the meat becomes firmer and denser, with shrinkage in volume.
Formation of gelatin. After the meat is heated in a moist atmosphere
to a definite temperature for a sufficient time the connective tissue dissolves.
If the concentration of gelatin in the liquid reaches 1.5 or higher percent-
ages, it forms a jelly when cooled. Connective tissue is composed largely of
collagen. Collagen is changed to gelatin more rapidly at higher tempera-
tures. Smith states that the phosphate ion accelerates the rate at which
collagen is changed to gelatin at a given temperature. The addition of acid
to meat may also increase the rate of hydrolysis of collagen.
Juiciness. Juiciness is given as a desirable quality of cooked meat. Meat
loses moisture during cooking, even when cooked submerged in water. The
higher the interior temperature to which the meat is cooked, if the composi-
tion and cooking conditions are standardized, the less moist the meat. Meat
that contains a large amount of fat within and around the muscle fibers
may seem juicy because of melting of the fat by heat in cooking. The fibers
with a high fat content may also have a high water content, particularly
if part of the fat is in an emulsion that will not break with high tempera-
tures, thus retaining part of the moisture.
Some pieces of meat are apparently far more juicy than others after
220 MEAT
cooking. It seems rather certain from the results of Hoagland et al., Grass-
man, and others, that the increase of amino nitrogen with aging is one
factor in bringing this about. The amino acids may not be able to bind as
much water as the protein, so that the free water content and apparent
juiciness may be increased with increase of amino nitrogen. Sometimes the
juiciness seems to be related to the fat content. How great an influence
the method of distribution of the fat within the fiber, the salt content of
the fiber, the />H, or the development and maturity of the fiber have upon
this point cannot be stated. The tissues of old animals lose their power to
bind as much water as tissues from younger animals. Although this may
partially explain the better quality of meat from younger animals it does
not explain why veal is less juicy than baby beeves. Perhaps, if the water
is bound too tightly by the coagulable protein micelles, the dryness is more
apparent to the tactile sense.
Child and Fogarty found that approximately 1 1 per cent more fluid
could be pressed from one semitendinosus muscle when heated to an in-
terior temperature of 58C. than for the other semitendinosus muscle from
the same animal heated to 75C.
Noble, Halliday, and Klaas found : "When subjected to a pressure of
3,800 pounds per square inch, the ribs cooked to 61 C. yielded more juice
than those heated to 75 C. and the round more than the corresponding
ribs. The larger quantity of juice was found to be richer in solids, total
nitrogen, and, in one case, also richer in coagulable nitrogen."
Empey states that for uncooked meat there is a direct relationship be-
tween the hydrogen-ion concentration of the muscle fiber and its capacity
for holding muscle fluid, but the author knows of no work in which
juiciness of cooked meat has been related to />H.
Change in color. During the heating of meat, after a temperature of
about 50C. is reached, the color gradually changes from red or pink to a
lighter shade and finally, if a sufficiently high temperature is reached, be-
comes brown or gray. Veal and pork are more gray, beef and lamb develop
a browner shade. This color change has been discussed in connection with
meat pigments, the oxyhemoglobin being broken down by heat to the brown
hematin. The degree of ripeness of the meat affects the temperature at
which the color change occurs, ripened meat becoming gray at a lower
temperature.
The extreme browning on the surface of meat is accompanied by break-
down of surface proteins and fat, probably with liberation of sulfur and
other compounds.
Tenderness. Methods of estimating. Tenderness is one quality uni-
versally desired in cooked meats. Tenderness may be estimated by subjective
methods such as the ease of cutting or chewing. At present the most widely
used method for comparing the tenderness of meat is the grading chart.
The chart developed by the Cooking Committee of the National Project,
TENDERNESS
221
"Cooperative Meat Investigations," uses seven numbers and terms to
designate the tenderness of the sample. They are: very tender, tender,
moderately tender, slightly tough, tough, very tough, and extremely tough.
Each judge forms his own standards from the basis of his experience. If the
judge has had a complete range of qualities on which to base his standards
and is consistent in adhering to them, he may become very proficient in
judging comparative tenderness.
Numerous mechanical devices have been devised for estimating the ten-
derness of meat. The ones most commonly used at present are : ( 1 ) the
shearing apparatus, which registers the number of pounds required to shear
a piece of meat of a given diameter; (2) the penetrometer, with which a
specially constructed needle may be used; and (3) a puncturing gage.
Results of tenderness tests. There has been considerable discussion as to
whether raw meat is tenderer or tougher than the same meat when cooked,
which to date has not been settled. Moran and Smith, after studying the
effect of ripening on tenderness of beef, say: "It is a matter of general
experience amongst those accustomed to raw meat that cooked meat is
tougher than raw meat." They also quote Stefansson from "The Friendly
Arctic" as follows: "Cooking increases the toughness and brings out the
stringiness. I have never eaten any raw meat that was noticeably tough or
stringy."
Black, Warner, and Wilson have reported that cooked samples were
more tender than raw samples from good and medium-grade three-year-
old grass-fed steers and steers fed both grain and grass. The number of
steers in each lot was eight, the number of tests for raw and cooked meat
was 12 and 4, respectively. Their results are given in Table 28.
TABLE 28
SHEARING STRENGTH OF RIGHT AND LEFT RAW TWELFTH-RIB SAMPLES AND
LEFT COOKED ELEVENTH-RIB SAMPLES (Blacky Warner, and Wilson)
Shearing
Shearing
strength
strength
Lot designation
raw
cooked
muscle
muscle
Ibs.
Ibs.
Good grade, grain on grass
72 9
32 7
Good grade grass alone
72 6
39
Medium grade, grain on grass
71.7
34.9
Medium grade, grass alone
78.3
38.8
Noble, Halliday, and Klaas found beef more tender, as tested by a
penetrometer, when heated to 61C. than to 75 C.
222 MEAT
Lowe compared the penetrometer and shearing apparatus by using both
tests to measure the tenderness of the longissimus dorsi of raw and cooked
beef rib roasts. The roasts were used in pairs, one roast being cooked, the
other left raw. Both methods indicated raw meat to be the tenderest, the
rare intermediate, and the well-done the least tender. But penetration
tests appear to be influenced by the density of the meat, the meat with
the greatest cooking losses, i.e., the well-done, being firmest. Thus penetra-
tion tests indicated no difference in meat from different animals when
there was little difference in firmness but where both the shearing tests and
grading score indicated a range in tenderness. The penetration depth was
greater in soft raw meat than in firm cooked meat, the differences being
highly significant. Shearing tests showed significant difference in the ten-
derness of the longissimus dorsi from animals of varying grade and the
values obtained were in agreement with the grading score. None of the
correlations between penetration and shearing tests were significant, from
which it was concluded that shearing was the better method for measuring
the tenderness of meat.
Means of increasing tenderness. The possible ways of increasing the
tenderness of meat may be classed as follows: (1) mechanical, (2) enzyme
action, and (3) by peptization and increased solubility of the proteins. The
first is a physical, the last two would bring about chemical changes.
Meat is ground to break the fibers and connective tissue, which, because
it lessens the need for chewing, increases the tenderness. For very tough
cuts this is probably the most satisfactory procedure. In tests that have been
made, it was found that meat, ground fine and several times as for
Swedish Meat Balls, is more juicy and palatable than meat ground medium
or coarse and only once.
Investigators have sought for suitable enzymatic and chemical means of
increasing tenderness of meat for years. The proteolytic enzymes found in
the meat increase the tenderness but considerable time at low storage
temperatures is required. Hence, if a proteolytic enzyme that would speed
up the breakdown of the proteins and which would give satisfactory results
were found the tenderness of meat could be increased in a shorter storage
period. Papain has been tried. The author's results to date with this enzyme
have not been satisfactory. When it was applied to the surface of the meat
some time was required for the enzyme to act and then only a thin,
powdery surface layer was formed. When it was applied just prior to cook-
ing the heat destroyed the enzyme, so that its application was of little or no
value. No satisfactory methods of injecting this enzyme have been reported.
Investigations that have been reported in connection with flour proteins
suggest that it is possible that meat may contain substances that tend to
inhibit the action of the proteinases of the meat and if some salt that would
counteract this inhibition through oxidation or other means could be in-
jected that the meat would become tender more rapidly.
TENDERNESS 223
The changing of collagen of the connective tissues or structural proteins
to gelatin during cooking is one means of increasing the tenderness of these
proteins, but the solubility of the protoplasmic proteins decreases when they
are coagulated by heat.
Another method of increasing the tenderness of meat would be through
the use of substances that would peptize both or either the connective or
protoplasmic meat proteins, thus increasing their solubility and the tender-
ness of the meat. Means of bringing about peptization have been discussed
in Chapter I. Sugar peptizes some proteins. Many electrolytes also bring
about peptization, particularly if mixed intimately with the substance to be
peptized. Anions of acids such as tartrate, citrate, and acetate may bring
about a greater or lesser degree of peptization. A practical peptizer, if such
could be found and used, would be a salt that could be injected and have
slight effect at low temperatures but bring about peptization fairly rapidly
when heated during cooking of the meat.
Smith states: "It is of interest to note that, in cases where the primary
aim of cooking is to make the meat more tender (as, for instance, in
stewing), the required degree of tenderness can be reached more quickly
by addition of phosphate, or what amounts to the same thing, since the meat
itself contains phosphate, of concentrated stock from a previous boiling.
The concentration of phosphate which gives the greatest effect is about
0.2M, but a quarter of this will have quite an appreciable effect. A suitable
mixture of mono- and di-hydrogen phosphates to give a />H between 6 and
7 was employed."
Meat is sometimes placed in a pickle of equal parts of vinegar and water
and is used for Sauerbraten or similar dishes. Soaking in the acid is sup-
posed to increase the tenderness as well as develop a particular flavor of
the meat. If the vinegar contains tannins, the meat should not be cooked in
an iron utensil, for a dark color will develop from the tannins combining
with the iron. The effect of the acid on the meat, which will probably
depend upon the amount of acid added and the resulting pH of the meat
and whether this pH is at, above, or below the isoelectric point of its
proteins, may cause the connective tissue to swell and hydrolyze the col-
lagen to gelatin more rapidly when the meat is heated. Tomatoes or sour
cream are also added to Swiss steak and tomatoes to stews. Sometimes the
acid appears to increase the tenderness; but often a paired cut without the
acid is as tender or more tender than the one to which acid is added.
Baker states that the lactic acid developed in the meat may be responsible
for improvement in tenderness. He says that Walsh investigated the develop-
ment of acidity in lean beef and claims that its formation is important in
the preparation of canned meats. Properly matured meat, after canning,
''melts in the mouth," the muscle fibers are softened, slicability is enhanced,
and the pink color is more vivid. But in maturing or ripening changes are
also brought about by enzymes and other means.
224 MEAT
Cooking of Frozen Meat
Frozen meat and poultry are obtainable in retail markets in larger cities.
In addition many people freeze meat in mechanical freezer units, and the
practise of obtaining compartments and freezing fresh meat in local cold
storage plants in rural and small urban communities is increasing tremen-
dously. Hence, the cooking of frozen meat attains importance and knowl-
edge of what happens to the meat during freezing gives understanding of
why it should be cooked soon after defrosting, if it is defrosted before
cooking.
Freezing. When meat is frozen, the unbound water forms ice crystals.
These crystals on thawing, with their dissolved substances tend to exude
from the cut surfaces of the meat. Empey found the drip from frozen and
thawed meat very similar in composition to fluid pressed from unfrozen
meat. He found a direct relationship between the hydrogen-ion concentra-
tion and the capacity of the muscle to hold fluid. Minimum drip occurred
when the />H of the muscles had not dropped below 6.3. However, he did
no work to determine the tenderness of the meat in connection with />H or
at what pH it would be most desirable to freeze the meat for quality and
palatability after cooking. The writer's experience thus far is that meat
that is not tender before freezing does not improve in tenderness by freezing.
This would indicate that for palatable meat it is preferable for meat to be
ripened sufficiently before freezing.
Meat may be frozen rapidly or slowly. In rapid freezing the meat is
subjected to a very low temperature so that freezing occurs in a short time.
The advantage of this method is supposed to be due to the fact that the ice
crystals have little time to grow; hence they are smaller and break the
fibers to a smaller extent. There is considerable controversy as to which
is the best procedure. Moran says that in their studies rapid freezing
possessed no advantages over slow freezing as regarded the quality of the
product, but that in each case the most important factor affecting the
quality was the storage temperature. Lowe and Keltner found no difference
in the quality of poultry frozen by rapid and slow methods. Many reports
in the literature indicate that it is preferable to keep the meat or poultry
at quite low temperatures, 10 to 15F., to prevent desiccation of
the meat. Tressler believes it is desirable to have the temperature as uni-
form as possible, for a fluctuating temperature also increases moisture loss.
Each piece of meat or bird should be wrapped to prevent moisture loss.
Tressler says, "Severe desiccation causes a considerable loss of flavoring
components, and makes the frozen product tougher, less easily cooked, and
therefore, less desirable for food."
Defrosting. The method of defrosting seems to be particularly im-
portant for poultry. Snyder found poultry defrosted in water markedly less
desirable in flavor than poultry defrosted in cold air, i.e., in a refrigerator.
THE USE OF SALT
225
The method of defrosting was also more important than drawing and length
of storage period in determining flavor, although the giblets of undrawn
birds were not so desirable as those of drawn birds.
Many questions are received from Iowa women regarding the flavor of
poultry frozen and stored in local plants. It is a common practise for
these women to defrost the poultry in water, but their frozen meat is
defrosted in cold air.
Beef and meats having extensive cut surfaces of the muscles tend to
"drip" more than poultry after defrosting. Since loss of this fluid also
FIG. 23. Standing rib roast of beef. Showing thermometer inserted for reading
interior temperature of the meat.
results in loss of flavor and nutritive value, it is desirable to cook the meat
soon after defrosting or even before defrosting. Defrosted meat is also
more susceptible to bacterial attack.
Cooking. Defrosted meat is cooked in the same way as unfrozen meat.
But if cooking is started before the meat is defrosted, then the temperature
and time of cooking need to be changed to allow the meat both to thaw
and to cook. Otherwise, a steak or roast can be served with a brown
appetizing exterior and still be frozen in the interior. The writer prefers
to start cooking all frozen steaks and chops before defrosting, as there is
then no loss of fluid and flavor. But the meat is not seared. The cooking
temperature must be low and the cooking time increased to at least 3 or 4
times longer than for unfrozen meat. Because of the longer time required
for thawing and cooking the exterior browns sufficiently without searing.
The use of salt. There is no advantage in salting large pieces of meat,
226 MEAT
as the salt is placed on the surface of the meat and does not penetrate
to any appreciable extent during cooking. Part of the salt is carried from
the surface of the meat by the juices and into the drippings. Snyder
determined the total and nitrogenous losses in beef roasts and stews. The
meat was all from the same carcass, the cooking conditions were standard-
ized, and the roasts or stews cooked in pairs. Similar cuts, cut as nearly
alike as possible by an experienced meat cutter, from the right and left
side of the animal, were used for each pair, one of the pair being salted,
the other left unsalted. The quantity of salt used was about the amount
that would be used by housewives in cooking meat, 1.5 grams per pound
of meat. The losses were determined on the basis of the uncooked weight
of the meat and on surface area, but both methods showed no appreciable
differences in the total or nitrogenous losses of the salted and unsalted
meats. In the salted roasts the flavor penetrated to less than ^ inch in
depth. The layer in which the salt had penetrated was a deeper gray in
color than the corresponding layer on the unsalted roast.
Records for cooked meats. In addition to the records of weight, time
of cooking, etc., a tracing may be made of the cut surface of roasts, steaks,
and chops. A piece of parchment paper is laid over the cut surface and
the entire surface rubbed lightly with the fingers to bring it in contact with
the meat. The fat leaves the paper semi-transparent, and the moisture from
the lean portion slightly puckers the paper. A pencil tracing is made
around the edge of the meat and the fat and bone layers. A tracing of this
sort is better than a photograph in that the dimensions are actual size. It
also shows the exact distribution of fat, lean, and bone. A good grade of
thin typewriter paper can be used for making these prints.
Methods of Cooking Meats
In general meat is cooked (1) by dry heat and (2) by moist heat. Dry
heat is generally used for tender cuts, such as roasts and steaks. The meat
is surrounded by dry air in the oven, under the broiler, or over coals, or
by hot fat. In general, moist heat is used for the less tender cuts and
includes methods by which the meat is surrounded by steam or water. This
includes cooking meat in water as for stews, in steamers, in casseroles, in
Dutch ovens, and even in roasting pans when the lid fits tightly and holds
the steam around the meat.
The tender cuts. In general these cuts include the prime-rib roasts,
steaks or roasts from the loin and sirloin, leg of lamb, fresh pork hams,
and pork, lamb, and veal chops.
Beef ribs. Prime-beef ribs may be cooked as standing roasts or the bones
may be removed for rolled roasts. Since the time of cooking varies with
many factors, it is difficult to state a definite time per pound for cooking
meat. Table 29 may be used for estimating approximate cooking time of
THE TENDER CUTS 227
one-rib and two-rib standing roasts. For three-rib standing roasts cooked
to an interior temperature of 57 C. an average time of about 20 to 22
minutes per pound is required when the experimental searing or 150C.
constant temperature methods are used. When the interior of the roast
reaches 57 C., the edges of the roast are contracting so that the large
center muscle of the ribs bulges. As the roast reaches the well-done stage,
all the muscles are contracted to a greater extent so that the large muscle
does not bulge as much as when the interior has reached only the rare or
medium well-done stage.
A rolled rib roast usually requires longer per pound for cooking than a
standing rib roast from the same cut. The rolled roast is usually more
compact in shape with a proportionally longer diameter, so that the distance
to the center is greater. See Fig. 25.
Lamb roasts. A leg of lamb is placed on a rack in an open pan, skin or
fell side up; but the fell is placed down for a shoulder rdast. The fell
can be removed, but Alexander found that its removal increases the cook-
ing losses, increases the cooking time, and does not increase the palatability
of the meat.
Alexander and Clark state that approximately 35 minutes per pound
may be allowed for cooking by the experimental searing or the 150C.
constant temperature methods, but considerable variation can be expected.
They found the cooking time for 750 legs of lamb, roasted by the Coopera-
tive Meat Investigation searing (experimental) method to an interior
temperature of 76C., varied from 25 to 58 minutes per pound, the small
poorly finished legs from cull carcasses requiring longer and plump well-
finished legs requiring a shorter time. The time is about the same, or some-
what shorter, for the 150C. constant temperature method, and is con-
siderably shorter if the leg is cooked to an interior temperature of 83 C.
Veal. Veal roasts may be cooked in open pans, the time per pound for
cooking varying widely with the size of the roast.
Pork. The Cooperative Meat Investigation cooking committee used for
the searing method 20 minutes at 250 to 255C, the remainder of the
cooking period being at 150C. For the present constant temperature
method, 175C. is used. A higher temperature is used with pork because
of the long time required on account of the slow rate of heat penetration
and the higher interior temperature to which pork is cooked, an interior
temperature of 78C. to 87C. being used. The official testing temperature
is 84C.
Steaks. Steaks from 1 to 2 inches in thickness may have a thermometer
inserted, the right-angle type being easier to turn for reading as the steak
is turned. An interior temperature of 60 to 63C., when removed from
the oven, gives a medium well-done steak. Steaks may be broiled below a gas
flame, under an electric heating unit, or over coals, or they may be pan
broiled. In broiling, the steak is placed far enough from the heat and
228 MEAT
turned often enough to prevent charring or over-browning. If desired,
the steak may be turned only once. For a rare or medium well-done steak
the cooking temperature does not need to be lowered, but for a well-done
steak, or for one thicker than \ l / 2 inches, the temperature may be lowered
after the browning is accomplished. Many people prefer steak cooked at a
constant, fairly low temperature. The interior of the medium well-done
steak is then more uniform in appearance, being pinkish throughout. Many
steaks cooked at high temperatures are likely to have a gray surface layer,
a thin pink layer, and an uncooked center portion. The outer surface of
the steak does not brown so well at the lower temperature, but these con-
noisseurs think this is more than compensated for by the uniformity of the
interior of the steak. Increased browning of the surface at the lower tem-
perature may be acquired by sprinkling with a small amount of sugar.
The searing time and the total cooking time vary with the temperature
used, the stage of cookery, and the thickness of the steak. The total time
for a medium-done steak 1 inch thick is 7 to 10 minutes when seared.
With a low, constant temperature the cooking time for the same steak may
be increased to 20 minutes.
Chops. Chops of veal, lamb, and pork may be broiled or pan broiled.
Thicker chops, at least % inch thick, but mutton, particularly, as thick
as 2 inches, are easier to cook without drying out than thin chops. The
time of cooking varies with the temperature and the thickness of the chop
from about 8 to 30 minutes. Pork and veal are usually cooked well done.
Pork chops require about 10 to 20 minutes, and chops of veal and lamb
% to 1 inch in thickness about 8 to 15 minutes.
Less tender cuts. The less tender cuts are used for pot-roasts, Swiss
steak, braised meat dishes, stews, and soups. If ground, the meat is cooked
as a tender cut.
The less tender cuts are usually cooked by moist heat and at fairly low
temperatures. The aim is to cook the meat so that the structural proteins,
the connective tissues, are softened yet not completely dissolved and the
plasma proteins of the fibers are not made tough, rubbery, or stringy. If this
is successful, a tender yet easily sliced meat is the result. If the connective
tissues are entirely dissolved, the meat is not slicable.
The less tender cuts are often pounded, or seasoned flour is pounded
into the meat, or the surface is floured and seared. Pounding appears to be
a good means of increasing the tenderness of some of the tougher cuts,
particularly those containing a great deal of connective tissue and little fat
or when they are not ripened. The flour absorbs and holds moisture; thus
to this extent the meat appears less dry. Better grades of less tender cuts
containing more fat and cuts from carcasses of younger animals from
which rigor has passed do not need to be pounded.
Cured meats. Some of the common cuts of cured pork are regular hams,
skinned hams, shoulders, shoulder butts, and bacon. The loin, cured, is
COVERED AND UNCOVERED PANS 229
sometimes called Canadian bacon. Cured lean meats, because of the action
of the salt during curing, are already fairly dry so they should always be
cooked to prevent as little moisture loss as possible. This is usually accom-
plished most easily by slow cooking at low temperatures.
Hams. Hams may be cured with a light or a heavy salt cure. The mild-
cured ones do not need soaking over night or parboiling before baking.
Hams with a heavy salt cure are improved in flavor by soaking over night
or for 24 hours.
Hams are roasted in open pans on a rack, fat side up, at 125C. (about
250F.) to an interior temperature of 70 to 75C. If the oven will not
maintain as low a temperature as this, 300F. may be used.
For cooking hams in water, a simmering temperature, 83 C., produces
a tender, juicy ham. Water temperatures as low as 75 C. may be used.
Hams cooked in water have the cooking losses decreased by cooling over
night in the liquor in which they were cooked, but the cooking losses are
influenced by the temperature of the liquor. Child found that the cooking
losses gradually decreased as the temperature of the liquor decreased. The
smallest losses, hence the greatest hydration of the ham, occurred at 1.6C.
(35F.). In fact the hams averaged a slight gain in weight when put in
the refrigerator and the liquor cooled to this temperature. With lowering
the temperature below 1.6C. the losses increased.
The time necessary for baking or cooking ham in water will vary with
the size of the ham and the cooking temperature used. For the tempera-
tures given, hams weighing about 12 to 13 pounds require about 23 to 25
minutes; those weighing 18 to 20 pounds require about 18 to 20 minutes
per pound.
Bacon. Bacon should be cooked at a temperature below the smoking
temperature of the bacon fat. Slow cooking at low temperatures is best.
For large quantities of bacon an excellent method is to spread the slices
on a wire rack, place in a pan, and bake in the oven at 160C. for about
18 minutes. The bacon needs no turning.
Covered and uncovered pans for roasting meat. Grindley and
Mojoinner state regarding the losses occurring in roasting beef in covered
and uncovered pans: "The total losses were greater when the meats were
roasted in a covered pan than when they were cooked in open pans, owing
chiefly to the increased amount of water removed. In the same time and at
the. same temperature the meat was more thoroughly cooked in the cov-
ered than in the open pans, possibly because the temperature of the meat
was higher in the closed pan." However, they based their conclusions on
results of experiments with 1 covered and 15 open pans.
The Cooking Committee of the Cooperative Meat Investigations uses
uncovered pans for cooking all experimental roasts and advises the use of
uncovered pans in the home. In general the cooking losses are less and the
meat more palatable in the uncovered pan, although with such very small
230
MEAT
roasts as half of a chicken opposite results may occur. The cooking time
is shorter when covered pans are used.
Pressure cooker. Gortner, in speaking of the moisture content of dried
biological materials, says it depends upon three variables : temperature,
pressure, and time. He adds that the moisture content of a sample should
not be given without a statement of the condition under which it was dried.
One question often asked is why meat cooked in a pressure cooker at a high
temperature is tender and not dry. The answer is determined by the meat
and these three variables. There would be a far greater tendency to dry the
fibers at a high temperature and in a partial vacuum.
^y"^* 88 *****^ IIIM&.
MMtt jim
f > ^- y r , .irriMi.O^^^^*--^^^*^^^- ' *m^^ : :^* Sf * A ' f
^^^^^^^^* imiMMm^Mimmmnroi^- 1 -
FIG. 24. Some types of skewers used for roasting meat.
The use of skewers. Muscle tissue conducts heat slowly. Most metals
conduct heat rapidly. Morgan and Nelson used skewers in cooking stand-
ing rib roasts. The skewers were made with a long, narrow portion, about
the size of a lead pencil, that was inserted in the meat. The other end of
the skewer was in a spiral to give greater surface for receiving the heat
from the oven, and thus conducting it into the meat. Pictures of the dif-
ferent types of skewers used in meats are shown in Fig. 24. They found
that "the roasting speed was increased 30 to 45 per cent when nickel-
plated copper skewers were used. Similarly, smaller and less regular de-
creases in total shrinkage of weight of meat were found in the skewered
as compared with unskewered roasts." They found the efficiency of the
skewers in shortening the cooking period greater when a high oven tem-
perature was maintained throughout the cooking period.
CONSTANT TEMPERATURE METHOD 231
Cooking Temperatures
The best cooking temperatures for meat may not be the same for all
conditions. As a general rule, it is agreed that low or medium temperatures
are better than high ones for cooking meat. Yet some samples of meat do
not seem to be toughened by any method of cooking; that is, if one
deliberately sets out to show that higher temperatures toughen a piece of
meat, while the same cut from the other side of the same animal cooked at
a lower temperature is tender, the results are often not consistent.
Advantages of low temperatures. In general, lower cooking tem-
peratures result (1) in less cooking loss, (2) in more juicy meat, (3) in
more uniformly cooked meat, and (4) in longer cooking time. The meat
is more uniform in color and more juicy throughout; whereas at a higher
temperature, the meat is more gray and dry at the surface, there being a
sharper contrast between the meat near the surface and that at the center
of the cut. A longer cooking time may be an advantage, for the home-
maker may safely leave the meat cooking while she attends church, etc.
Disadvantages of low temperatures. Often the meat (1) does not
brown as attractively at the lower temperature, although occasionally the
opposite is true, and (2) a longer cooking time is required. A long cooking
time may also be a disadvantage.
Searing method. The Cooking Committee of Cooperative Meat In-
vestigations formerly used a searing method for cooking experimental roasts
of fresh meat. The roast was seared for 20 minutes at 250 to 275C.
(about 480 to 525F.) and was then transferred to a second oven at
125C. for the remainder of the cooking period. It was necessary to transfer
experimental roasts to a second oven so that results from different labora-
tories could be compared, for different ovens cool at different rates. Obvi-
ously the homemaker cannot use two ovens. Hence a lower temperature,
200 to 240C. (about 400 to 450F.), is recommended for the house-
wife in searing because the oven will remain at a fairly high temperature
for some time after the temperature control has been set at the lower
temperature.
Searing. Searing browns the meat, develops a characteristic surface
flavor, and starts the cooking. Often the statement is made that searing by
coagulating the muscle tissue on the surface prevents loss of interior fluids
and extractives. Searing increases the cooking losses, though the losses
may be largely surface ones. Searing also does not prevent the loss of
interior juices in all instances.
Constant temperature method. At present the Cooking Committee
uses a constant oven temperature 150C. (about 300F.) for cooking
experimental roasts, with the exception of pork, which is cooked at 175C.
(about 350F.). At this temperature the cooking time and losses are prac-
232 MEAT
tically the same as for the searing method formerly used. The exterior is
also browned to about the same extent, although it is sometimes less brown.
The homemaker will find that in using a constant temperature excellent
roasts will be obtained if she uses 150, 125, or 175C. Some ovens will
not hold as low a temperature as 125C. (250F. ), even though the
regulator carries this temperature. The meat will not brown as readily at
the lower temperature, but this can be overcome by using a mixture of salt
and sugar or sugar alone to sprinkle over the meat. The meat cooked at
175C. will not be as uniformly cooked as at the lower temperature.
Stages to Which Meat Is Cooked: Rare, Medium, and Well Done
The longer a piece of meat is cooked, the more the interior color changes
from pink or red to gray, and the greater the cooking losses. Some meats
like veal and pork are cooked well done, whereas beef may be cooked rare.
There is no definite stage between a rare and a medium-done piece of meat
or between a medium well-done one and a well-done one. The meat passes
from one stage to another gradually, so that there is no definite end point.
Heat penetrates slowly into the interior of a large piece of meat, and the
center of the meat, unless very much over-cooked, never attains as high a
temperature as the meat near the surface.
Rare meat. Grindley and Sprague have suggested, for convenience, that
meat with an interior temperature at its center of 60C. or below be called
rare. Such meats are juicier than meats cooked well done. Nearly all the
interior may be a bright red color or only a small portion around the center
of the meat may be red. The extent or uniformity of the red color depends
upon the cooking temperature. As the heat penetrates the meat the color
near the surface becomes gray. If the cooking temperature is high, this gray
layer may extend nearly to the center of the meat. If the meat is cooked at
a low temperature the gray color extends only a short depth and the color
of the interior of the meat is nearly uniform. Thus it can be seen that if
different cooking temperatures are used the interior of different pieces of
meat cooked to the same inner temperature may vary decidedly in appear-
ance. The intensity of the red color may vary with other factors as well as
with the cooking temperature. The interior of cooked meat ripened 40 to
60 days is grayer in color than meat that has not been ripened. Veal cooked
to the same inner temperature, and with the same cooking temperature, is
grayer, and has less red color, than beef. Rare meat also has more of the
original meat flavor than well-done meat, for not so much of the fluids and
extractives giving flavor to the meat has been lost.
Medium well-done meat. Grindley and Sprague have suggested that
meat that has reached an inner temperature of 60 to 70C. be called
medium well done. Here the color also varies with the temperature of
cooking, the degree to which the meat has been ripened, and in some in-
FACTORS AFFECTING THE TIME IN COOKING MEAT 233
stances with the age of the animal and the kind of meat. Rare and medium
well-done meats are probably more often associated with the color of the
cooked meat. Since the color of the cooked meat varies with different con-
ditions, the division into rare, medium well done and well done on the
basis of inner temperature of the meat is only an arbitrary one and not
always satisfactory. Most people would be agreed that medium well-done
meat should not be a deep red or pink, but should show some pink color.
Well-done meat. Meat that has a uniform gray color throughout the
entire interior of the meat is usually called well done. With veal, this
stage of cookery is sometimes reached before or by the time the inner tem-
perature of the meat has reached 71C. This may also be true of beef that
has ripened sufficiently. Unripened beef requires a higher temperature than
7lC. before a uniform gray color is attained, when a low cooking tem-
perature is used. But to some persons the term well done is associated with
the degree of cookery, that is, the separation of the muscle fibers due to
formation of gelatin from the connective tissue. It may also refer to the
dryness of the meat and the loss of juices. The meat may be cooked until
it reaches a temperature far above 7lC., often from 80 to 85C. for
roasts and from 95 to 99C. for braised meat.
Factors Affecting the Time Required for Cooking Meat
Directions for cooking meat usually state the time of cooking in terms
of minutes per pound. At best this can only serve as a guide, for several
factors may cause variation in the length of time required to cook a piece
of meat. The only way of knowing when the interior of a piece of meat
has reached a definite temperature and thus a definite stage of cookery is
to insert something in the center of the meat by which the interior tem-
perature may be read. For this purpose a thermometer or a thermocouple
may be used. The easiest method for household use is the insertion of a
thermometer into the meat. Two types of thermometers may be used : a
right-angled thermometer with the temperature scale on the horizontal arm
(see Fig. 23) ; or a very short tube-type thermometer about 6 or 8 inches
long with the temperature scale on the upper half. The latter must be short
to keep the top from touching the upper part of the oven, particularly the
small gas ovens and many electric ovens. Thus the graduated scale is con-
densed, which makes it more difficult to read. The short thermometer is
preferable for small roasts of meat and for meat with soft fibers. The right-
angled thermometer is suitable for beef roasts, ham, leg of veal, and lamb.
It is convenient for taking temperatures of custards, cakes, and other foods,
for it can be supported by the horizontal arm from a shelf in the oven.
The following factors affect the time required to cook meat. ( 1 ) The
cooking temperature. (2) Weight. Surface area. The shortest distance to
the center of the thickest portion of the meat. (3) The stage to which the
234
MEAT
meat is cooked rare, or well done. (4) The composition of the meat.
(5) The degree of ripeness.
The cooking temperature. The higher the cooking temperature the
more rapidly will a piece of meat reach a definite temperature, for with
a higher temperature at the surface, the more rapidly heat will penetrate
to the interior of the meat. As oven temperatures during the cooking of
meat may vary many degrees, this factor causes a wide variation in the
time required for cooking meat.
Diagram A
10
Diagram C Diagram D
FIG. 25. To illustrate heat penetration in roasts and to show that the diameter
does not increase in the same ratio as the weight.
Weight. Surface area. Shortest distance to thickest portion of
the meat. The time for cooking meat is often expressed in minutes per
pound, but it is also a well-known fact that a heavy piece of meat of the
same shape as one of light weight will require a shorter time per pound
for cooking if the oven temperatures are the same. The reason for this
can best be explained with the aid of a diagram. Suppose a cube 1 inch
square weighs 1 ounce. It contains 6 square inches of surface area (see Fig.
25, diagram A), and the distance from the sides to the center (s c in the
figure) is ^ inch. If the cube is enlarged to 10 times its original size, dia-
gram B, its weight is increased to 1000 ounces, its surface to 600 square
TIME PER POUND 235
inches or 100 times its original surface area, and the distance (s c) to
the center is 5 inches, or 10 times the distance of cube A. In other words,
the distance to the center does not increase in the same ratio as the surface
area and the weight. In heating these cubes, if the heat travels through the
material at a uniform rate it will not take 1000 times as long to bring the
center of cube B to a definite temperature as cube A, but 10 times as long.
The diameter of a sphere or a cylinder does not increase in the same pro-
portion as the surface area and weight. A piece of meat is not shaped like
a cube, but some are cylindrical, and in roasts of similar shape the weight
increases more rapidly than the distance that the heat must penetrate.
Rolled roasts are cylindrical in shape. Here the length of the radius
(r) determines the time for the heat to penetrate to the center of the
roast, unless the length of the cylinder is shorter than its diameter. See Fig.
25, diagram C.
In a standing rib roast, Fig. 25, diagram D, it is not the distance to the
center of the meat, which may be somewhere near the portion marked *,
but the distance through the thick portion of the meat, which affects the
time required for cooking. The heat travels in from the top along the line
tc y from the side along the line sc, and from the bottom along the line be.
Ham, leg of lamb, and leg of veal have the thickest portion of the meat
nearer one end than the center of the meat.
It is obvious from the diagrams that the shorter the distance to the center
of the piece of meat the more rapidly the heat will penetrate; the longer
the distance, the more time will be required. Weight and surface area are
not satisfactory to determine cooking time, for the size of the piece and
its shape determine the distance to the thickest part of the meat. A thin,
wide roast will cook in less time and a thick compact one will take a longer
time. The following examples illustrate this. A standing rib roast weigh-
ing 11.6 pounds required 1 hour and 52 minutes to reach an inner tem-
perature of 57C., when cooked for 20 minutes at 275C. and for the
remainder of the cooking period at 125C. This gives an average of 9.3
minutes per pou'nd. Another roast weighing 11.5 pounds and with the same
cooking conditions required 3 hours and 43 minutes, averaging 19.3 min-
utes per pound. The first roast consisted of five ribs and was thin and wide ;
the latter consisted of three ribs and was thick and compact. If roasts are
always of the same shape and the same cooking temperature is always
used the time for cooking can be estimated more accurately than when the
shape of the roast varies.
A large piece of meat cooks in a shorter time per pound than a small
one if all other conditions are standardized. Smaller hams and legs of
lamb require more minutes per pound than larger ones. The same is true of
poultry, smaller chickens and turkeys requiring more minutes per pound
than larger ones.
Time per pound. Minutes per pound for some roasts are given in
Tables 29 and 30, but if not taken in connection with cooking tempera-
236
MEAT
tures, size, and the stage of cookery, they are worth very little for a guide
in cooking meat. Most of the roasts given in these tables were transferred
to a second oven after searing instead of lowering the temperature of the
oven in which the roast was seared. This gives a slightly longer time per
pound. There may be considerable variation in the time per pound as can
be seen in Table 29. In general, the time per pound is longer with the
smaller roasts. With a very thin roast the thickness of the slice influences
the rate of heat penetration more than the other dimensions or its weight.
TABLE 29
THE TIME OF COOKING PER POUND AND COOKING LOSSES IN ONE-RIB AND
TWO-RIB BEEF ROASTS COOKED TO DIFFERENT STAGES.
SOME CLASS RESULTS
No. of
Weight
Searing
Cooking
Interior
temper-
ature
Cooking time
Total
ribs
in
temper-
ature
0/^1
temper-
ature
Q/->
when
removed
Total,
Time
cooking
losses,
roast
grams
pounds
c.
C.
from
min-
per
per cent
oven
utes
pound
One
836
1.8
275
125
55
59
33.0
8.4
Two
1560
3.4
275
125
55
93
38 2
11.8
Two
2331
5.1
275
125
55
100
19.5
10.9
Two
2813
6.2
275
125
56
124
20.0
15.1
One
835
1.8
275
125
65
81
45.0
11.0
Two
1575
3.3
275
125
65
116
33.3
14.9
Two
1626
3.6
275
125
65
140
36.0
14.8
Two
1890
4.2
275
125
65
110
26.3
14.0
One
757
1.7
275
125
75
85
50.0
20.0
Two
1603
3.5
275
125
75
190
53.3
21.4
Two
1758
3.9
275
125
75
127
32 . 5
25.0
Two
2268
5.0
275
125
75
260
52.0
20.2
Surface area. Since time per pound does not give a dependable basis
for cooking meat an effort is often made to express cooking time in relation
to the surface area. Often this is expressed in the following way. The
greater the surface area the shorter the time required for cooking a piece
of meat if all other conditions are standardized. From the diagrams, Fig.
25, it can be seen that this method would give a less variable cooking time,
at least for some pieces of meat of certain shape, than time per pound.
This method of expressing time for cooking is also more difficult to deter-
mine in the home.
TEMPERATURE OF MEAT 237
Stage to which the meat is cooked. Cooking meat rare does not re-
quire so long a time as cooking medium well done or well done, because
the last two stages require a higher inner temperature. See Table 29.
The composition of the meat. The proportion of fat and lean in the
meat affects the time required for cooking. There has been much confusion
regarding the rate of heat conduction by fat. In physiology, one is told that
a layer of fat over the muscles prevents loss of body heat, because the fat
is a poor conductor of heat. In articles on cooking various foods, one often
sees the statement that fat conducts heat more readily than muscle tissue.
These two seemingly contradictory statements are explainable. Redfield has
offered a solution. In studying the rate of heat penetration in canning pork
and beef, she found, with all other conditions standardized, that the tem-
perature at the center of the can of pork rose more slowly than the tem-
perature at the center of the can of beef. In order to determine whether
this slower heat conduction in the pork was due to its greater fat content,
she packed some cans with suet and others with beef round free of all
visible fat. She found that the temperature of the suet rose more slowly
than that of the beef round until the melting point of the suet was reached.
As soon as the fat melted, it conducted the heat faster than the beef round.
Fat in a liquid form in cooking is a good conductor of heat, but if it is in
a solid form it is a poor conductor of heat. In Redfield's experiments, the
fat escaped from the fat cells, the connective tissue forming a piece about
the size of a marble around the point of the thermocouple.
The writer's experimental classes, in processing suet, fat pork, lean beef,
and lean pork in pint cans in a hot water bath, have found the rate of heat
penetration to be much slower in the fat meat than in the lean, even at
temperatures of 90 C. and above. When the suet was packed tightly into
the jar so that the tissues surrounding the fat cells were broken, Redfield's
results were checked.
Degree of ripeness. Alexander and Clark found that increasing the
length of the ripening period after slaughter shortened the time required
to roast leg of lamb. As the ripening period increased beyond two days
after slaughter, the cooking shrinkage became smaller and the rate of heat
penetration more rapid.
Thus it seems that, if the connective tissue remains unbroken, as it does
in the more solid fat and the interior fat of meat cuts, it prevents the fat
globules from touching each other and delays heat penetration.
Rise of Interior Temperature of Meat after the Cooking Process
Has Been Stopped
When a roast is removed from the oven or a piece of cooked meat is
removed from the cooking utensil the temperature in the interior may con-
tinue to rise. Heat is carried to the interior of the meat by conduction, that
is, from fiber to fiber. When the cooking process is stopped the temperature
of the meat half way to the center is higher than the temperature at the
238 MEAT
center. This heat is conducted both toward the center and the outer edge
of the meat, and as a consequence the temperature at the center of the
meat rises.
The factors that may determine the extent of this rise in temperature
after removal from the oven are: (1) the cooking temperature; (2) the
inner temperature of the meat when the cooking process is stopped; (3)
the size of the piece of meat; (4) the composition. It must be remembered
that each of these factors may have an influence on the temperature rise
of the same piece of meat, and that under some conditions one factor may
influence it more than another. Thus they cannot be considered separately,
for the high cooking temperature of a steak or roast may affect the tem-
perature rise more than the size. Yet under some conditions size is a greater
factor in determining temperature rise.
Cooking temperature and temperature rise after the cooking
process is stopped. The higher the cooking temperature the greater the
tendency for a rise in the inner temperature of the meat. A higher cooking
temperature produces a higher surface temperature, and consequently results
in a higher rise at the interior after the cooking process is stopped.
Inner temperature. The lower the inner temperature at which the
cooking is stopped, the greater the tendency for the rise of inner tempera-
ture. This is because with a low inner temperature there is a wider varia-
tion between the inner and surface heat, which results in greater rise of
inner temperature. The inner temperature of foods that contain a high
percentage of water, such as cake, meat, and potatoes, never rises above
the boiling point of their juices. Heat supplied in amounts greater than
the amount needed to reach the boiling point of the juices is used in
evaporating the liquid. It is impossible to raise the inner temperature of
meat above 100C. without having a very dry, charred product.
Size. In larger pieces of meat, the size of the piece is not so important
a factor as those mentioned above in affecting the temperature rise of the
interior after cooking has been stopped. But a piece of meat may be so
small or thin that the inner temperature does not rise after the cooking
process is stopped, because of the rapid cooling from the surface.
Composition and duration of temperature rise. No definite relation
has been established between composition of the meat and the extent of the
inner temperature rise after cooking. It does seem to affect the duration
of the temperature rise more than the extent. Meat containing a great deal
of fat and meat that has a very thick layer of fat on the surface, 24 to 1
inch or more, requires a long time for the inner temperature to reach its
maximum point. A roast with such a layer of fat may take as long as 1
to 1^2 hours to reach its maximum inner temperature, whereas a lean roast
of the same shape, and cooked under the same conditions, may take only 12
to 30 minutes to reach its maximum interior temperature, after the cooking
process is stopped.
METHOD OF COOKING AND COOKING LOSSES 239
Factors Affecting the Losses That Occur During the Cooking
of Meat
The total loss that occurs during the cooking of meat includes the losses
known as drippings and the volatile losses. The greater part of the volatile
loss is from evaporation of water. It may include volatile substances from
the decomposition of fat and volatile aromatic substances. The drippings
include fat, water, salts, and both nitrogenous and non-nitrogenous ex-
tractives.
Time, stage of cookery and losses. The stage of cookery is one fac-
tor that affects the cooking loss. Meat cooked rare gives less total cooking
loss than meat cooked well done. A longer time is required to reach the
well-done stage, if all other conditions are the same. Thus length of time
of cooking and the stage to which the meat is cooked are related factors.
Composition and cooking losses. Meat containing a high percentage
of fat cooked under standardized conditions gives greater cooking losses than
lean meat. The amount of drippings is always greater for the fat meat
than for similar lean cuts from the same kind of animal. This is also true
for poultry. Cooking temperatures that melt the fat cause a heavy fat loss
from the meat.
Surface area and cooking losses. The shape and surface area of the
meat also influence the loss that occurs during cooking. The greater the
surface area of the meat, the greater the area at which losses may occur.
Compact pieces of meat with correspondingly small surface areas give
smaller losses than irregular-shaped pieces with greater surface areas.
Cooking temperature and cooking losses. The cooking tempera-
ture is in many instances the principal factor in determining the percentage
of weight that is lost during cooking. Occasionally time may be a more
important factor than cooking temperature in its effect on the resulting
losses. For example, cooking losses were greater for halves of chicken roasted
at 125C. (about 250F.) than for the corresponding halves roasted at
175C. (about 350F.). In the former instance, twice as long was required
for the interior of the thigh to reach 85C. (185F.). Alexander and
Clark found similar results for very small, poorly finished legs of lamb.
However, in general the higher the cooking temperature the greater the
cooking losses; the lower the cooking temperature the smaller the cooking
losses. Intermediate cooking temperatures give corresponding intermediate
cooking losses.
Method of cooking and cooking losses. The method of cooking the
meat may also influence the cooking loss. A broiled steak may have a far
greater total loss than a pan-broiled one, yet the interior of the meat may
be just as juicy. The radiant heat as well as the temperature reached usually
causes a high fat loss from the edge of the boiled steaks, whereas a pan-
broiled one may have a small fat loss.
240 MEAT
Degree of ripeness. Alexander and Clark found cooking losses de-
creased with longer ripening.
The Losses Occurring in Cooked Meats
The cooking losses vary with the factors mentioned, time, stage of cook-
ery, cooking temperature, surface area, and composition. Usually, the longer
a piece of meat is cooked, the greater the cooking losses; but this is not
always true in practise, for owing to differences in surface area and com-
position of different meats, it is not possible always to standardize all
conditions.
Meats show wide variations in cooking losses. The cooking losses
in meat may vary from 5 per cent to 50 per cent. This is a wide variation.
Obviously, meat that has lost 50 per cent of the uncooked weight is either
very dry or has lost an immense amount of surface fat. Swiss steak was
cooked to determine the effect of different percentages of loss on texture
and palatability of the meat. The ones with 50 per cent loss w^ere very
dry and unappetizing, even for a person who prefers meat very well done.
Here there was little surface fat, because of the cut and type of meat
used. A roast with a great deal of surface fat may suffer a rather high
loss and be far more palatable than a lean piece of meat. But, in general,
a 40 to 50 per cent loss leaves the meat much too dry.
Well-done meat usually shows greater cooking losses. In general, meats
cooked rare sustain less loss; the losses may vary from 5 to 20 per cent.
Under some conditions they may be higher. Well-done meats usually have
a higher cooking loss, from 20 to 45 per cent. However, meats cooked until
well done at very low cooking temperatures may have less than 15 per cent
cooking losses, so that it is impossible to give definite figures for any
definite stage of cookery.
In Table 30 some cooking losses are given, and since cooking losses
without cooking temperatures and stage of cookery mean little, these are
included. The composition of the meat and relative surface area are not
indicated.
Cooking losses in steaks and chops. The losses in steaks may vary
to a great extent, but usually seem to come within 10 to 40 per cent, when
ordinary cooking methods and cooking times are used. High cooking tem-
peratures cause a greater fat loss from around the edge of the steak and
also brown it better, giving a more attractive appearance, unless the tem-
perature is so high that the fat is charred. A steak may be cooked at a
high temperature, and have a greater loss, due to -high temperature, yet
be rare in the center, because of a shorter cooking time, than a steak cooked
at a low temperature. Steaks and chops that are cooked rare or medium
well done may lose from 10 to 25 per cent of the uncooked weight. Steaks
and chops cooked well done usually have higher losses, from 20 to 40 per
cent. The above figures are taken from losses obtained in cooking steaks and
LOSSES IN MEATS COOKED IN WATER
241
TABLE 30
COOKING LOSSES OF ROASTS
A irf*r
Aver-
Interior
Total cooking losses
r\Vcr
Sear-
Cook-
age
tempera-
Investigator
Kind of meat
and cut
No.
roasts
age
weight
of
roasts,
ing
temper-
ature
ing
temper-
ature
time
per
pound,
ture when
removed
from
Aver-
age,
Mini-
mum,
Maxi-
mum,
pounds
c.
c.
min-
oven
per
per
per
utes
C.
cent
cent
cent
Dowler
Pork, rolled loin
6
3.97
250
150
34.5
77
27.4
20.0
31.0
Hunt
Beef, standing,
6
6.26
275
125
18.3
57
16.6
10.6
21.3
3-ribs
Kite
Beef, standing,
5
6.98
250
250
16.7
70
41.2
35.4
47.3
3-ribs
Lowe
Beef, standing,
43
4.65
275
125
22.4
57
10.8
7.2
17.4
3-ribs. Feeders
Beef, standing,
65
8.95
275
125
19.8
57
13.0
6.6
18.4
3-ribs. Fattened
Beef, ribs rolled
5
14.09
260
125
17.8
57
10.3
7.9
14.4
Pork, loin
5
1.44
275
150
69.0
80
27.4
20.0
31.0
Ham, baked
3
12.2
150
125
22.9
70
15.4
14.4
17.7
Ham, baked
5
19.5
150
125
17.8
70
22.6
15.8
26.6
Ham, boiled
3
18.6
85
85
18.6
70
16.3
12.4
31.5
Lamb, leg
3
5.00
275
125
36.9
75
13.3
7.1
16.8
Snyder
Beef, rump
2
7.38
275
125
21.4
57
12.7
12.1
13.4
Shoulder round
2
5.29
275
125
22.9
57
7.9
6.9
8.9
boned and
rolled.
Chuck ribs
2
4.88
275
125
24.7
57
9.9
9.9
9.9
chops in class work. They are approximate and do not apply to all con-
ditions. Steaks and chops put in a cold pan and cooked at a low tempera-
ture for the entire cooking period show low cooking losses. They are juicy
but do not brown as well as ones seared at a high temperature, and the fat
does not brown well.
Losses in meats cooked in water. The losses of meat cooked in water
kept at a boiling temperature are usually higher than those cooked in water
held at a temperature of 85 C. or lower. Often the loss is twice as great
in the boiling water. The extent of surface area, composition, and time of
cooking affect the loss. Commercially boiled hams are often cooked at a
temperature of about 75 C., for this results in a lower cooking loss, about
15 per cent, which gives a texture that cuts and slices well. One very lean
242
MEAT
ham cooked in the laboratory in water at 82 with a total cooking loss of
12.4 per cent sliced well and had an excellent flavor. A cooking loss of
20 to 25 per cent seems to give a flavor to the ham that is preferred by
most persons.
The Percentage of Cooked Meat That Is Edible
Van Arsdale and Monroe have reported their results on "The cost of
meat as purchased and eaten." The following table is compiled from their
results.
TABLE 31
COST OF MEAT AS PURCHASED AND EATEN (Fan Arsdale and Monroe}
Kind of meat
Number of
chops, etc.
Per cent
edible
Purchase
price per
pound
Cost per
pound
cooked edible
portion eaten
Rib lamb chop
6
21.00
$0.28
$1.360
(Frenched)
Rib lamb chop
6
26.39
0.28
1.110
Loin lamb chop
6
44.20
0.28
0.646
Loin pork chops
6
48.00
0.23
0.483
Ham
1
43.80
0.19
0.433
Round beef steak
6
59.61
0.25
0.421
Porterhouse steak
2
56.27
0.30
0.522
Pot roast
1
54.85
0.26
0.485
Fowl
1
23.00
0.25
1.080
From the figures of Van Arsdale and Monroe it will be seen that the
loin lamb chops have higher percentage edible portion that the rib lamb
chops. Determinations of the weight of the cooked edible portion of rib
and loin pork chops made in the author's laboratory give similar results,
i.e., the loin pork chops have less waste than the rib pork chops. The
percentage of edible round beef steak given by Van Arsdale and Monroe's
results is much lower than the total edible portion for this cut of beef, on
account of the large percentage of the portion served which was not eaten.
Monroe and Van Arsdale have published results of experiments with roasts
of beef, veal, lamb, and pork.
The most extensive work on determining the weight and amount of
edible and servable meat with which the author is familiar is that of Mc-
Elhinney. This work was done in the Institutional Laboratory at Iowa
State College. The figures in the following tables are compiled from Mc-
Elhinney's results.
POULTRY
243
The searing temperature for all the meats with the exception of the
ham was 250 to 275C. for 20 minutes, and they were then cooked at
125C. for the remainder of the cooking period. The baked hams were
cooked at 150C. for 30 minutes and then at 125C. for the remainder
of the time. For the boiled hams a pint of water was allowed for each
pound, and they were cooked at a temperature of 82 to 83C. The degree
of doneness was determined by the use of a chemical thermometer inserted
into the roast as previously described.
TABLE 32
THE AVERAGE COOKING LOSSES AND TIME REQUIRED TO COOK DIFFERENT
KINDS OF MEAT (McElhinney)
Inner
Maxi-
Kind of
meat
Number
of
roasts
Total
weight
of all
roasts
Weight
after
cooking
Total
cooking
loss,
per cent
Minutes
per
pound
for
cooking
temper-
ature
when re-
moved
from
oven,
mum
interior
temper-
ature
reached,
op
Ibs. oz.
Ibs. oz.
c.
V_/.
Prime ribs,
well done
3
31 4
24 10
22.5
14.6
76
80
Prime ribs,
medium
5
60 9
47 10
21.7
9.8
65
70
Ham, boiled
5
104 5
82 12
20.6
17 .4
71
74
Ham,
roasted
7
126 15
94 7
25.6
14.1
72
77
Veal, leg,
roast
6
107 2
76 1
29.0
17.2
71
75
Lamb, leg,
roast
4
26 11
18 13
28.0
17.0
79
80
Pork loin,
roast
9
74 5
56 3
26.3
16.2
83
85
Poultry
Vernon determined the shrinkage in dressing and cooking poultry, using
fryers, roasters, and hens. Lowe and Vernon determined the dressing and
cooking losses for broilers, fryers, roasters, capons, and hens. All the poultry
was roasted except the fryers and broilers. The broilers were broiled under
a gas flame in the oven, the fryers were dredged in flour and fried in fat.
In frying, the lean fryers absorbed fat, and the fat ones lost fat.
The inedible portion includes the weight of all parts of the fowls served
but not eaten.
244
MEAT
TABLE 33
AVERAGE AMOUNT or WASTE AND PERCENTAGE EDIBLE OF DIFFERENT KINDS
OF MEAT (McElhinney]
Waste
Meat
Per cent
Per cent
edible
Meat
edible
slicable
Kind of
but not
slicable
on as
on as
meat
Drip-
pings
Bone
Skin
slicable
pur-
chased
pur-
chased
Ibs. oz.
Ibs. oz.
Ibs. oz.
Ibs. oz.
Ibs. oz.
basis
basis
Prime ribs,
well done
3 4
4 2
5 15
13 9
62.4
44.5
Prime ribs,
medium
6 1
9 12
15 3
22 3
61.2
39.4
Ham, boiled
10 3
8 14
7 8
18 8
37 12
53.8
36.2
Ham,
roasted
29 6
11 8
2
21
47 13
55.7
37.8
Veal, leg,
roast
11 2
9 6
12 12
46 7
55.3
43.3
Lamb, leg,
roast
6 13
4 3
3 7
9 8
48.5
37.1
Pork loin
9 11
10 8
8
31 1
51.0
40.4
TABLE 34
COST OF COOKED EDIBLE AND SLICABLE MEAT (McElhinney)
Cost cooked
Cost of slicable
Cost
edible meat
meat
per
Kind of meat
pound
as pur-
per
per
chased
per
pound
4-o u nee
serving
per
pound
4-ounce
serving
cents
cents
cents
cents
cents
Beef, well done
25.0
40.4
10.1
58.6
14.7
Beef, medium
25.0
42.1
12.4
65.2
16.3
Ham, boiled
30.0
57.8
14.4
90.2
22.5
Ham, roasted
33.0
60.5
15.1
88.3
21.8
Veal, leg, roast
28.0
49.5
12.4
63.2
15.8
Lamb, leg, roast
37.5
81.7
20.4
107.4
26.8
Pork loin, roast
27.0
55.3
13.8
71.4
17.8
ROASTING OF POULTRY
245
TABLE 35
DATA FOR DRESSING AND COOKING LOSSES OF DIFFERENT CLASSES OF POULTRY
BASED ON PER CENT OF LIVE WEIGHT (Lowe and Vernon)
Broilers
Fryers
Young
roasters
Capons
Hens
Average
all classes
Number of birds. . . .
Dressed weight
Drawn weight
13
89.1
62 9
14
89.9
67 8
9
88.9
70 6
10
90.0
75.6
16
92.0
71.4
62
89.9
69.6
Cooked weight
45.2
51.5
55.8
53.8
49.2
51.1
Fat loss
2.9
9.2
9.0
Moisture loss
10.1
12.2
12.3
Total cooking loss . .
Weight of inedible
cooked portion . . .
Weight of cooked
meat
Weight of drippings.
Weight of cooked
meat and drip-
pings
15.7
12.8
32.4
0.6
33.0
14.6
11.1
39.4
13.0
14.2
41.7
6.3
48.0
21.4
10.8
42.9
13.2
56.1
21.3
10.6
38.7
11.6
50.3
17.2
11.9
39.0
The term dressed weight is used as in poultry classification and market-
ing. A dressed bird is bled and has the feathers removed. Market prices
from butcher shops are usually for the dressed and not the drawn weight.
The drawn weight is the weight after removal of the head, feet, and diges-
tive organs.
As given in Table 35, the average losses for all classes of poultry are
12, 20, 19, and 12 per cent for dressing, drawing, cooking, and inedible
loss, respectively. Thus the cooked meat is less than 40 per cent of the
live weight.
For the convenience of those buying poultry from the markets, the data
in the preceding table are given in the following table, but based on the
drawn weight, which makes the percentages higher.
Lowe and Keltner found that the edible meat without skin, based on the
uncooked weight of 116 halves of roasters as prepared for the oven, aver-
aged slightly more than 50 per cent. When the skin was included the
edible portion was considerably higher.
The cost of the edible meat and of the total edible portion for the dif-
ferent classes of poultry given in Tables 35 and 36 is given in Table 37.
Roasting of poultry. The percentages lost in cooking poultry reported
by Lowe and Vernon, and tabulated in Tables 35 and 36, were obtained
by roasting the chickens in tight-fitting covered roasters at 250C. for 30
minutes and then the temperature was lowered to 175C. The pans were
246
MEAT
TABLE 36
DATA FOR DRESSING AND COOKING LOSSES OF DIFFERENT CLASSES OF POULTRY
BASED ON THE DRAWN WEIGHT, PER CENT
Broilers
Fryers
Young
roasters
Capons
Hens
Average
all classes
Number of birds. . . .
13
14
9
10
16
62
Drawn weight
97.0
97.4
97.5
99.1
98.5
97.9
Cooked weight
71.8
75.9
79.1
71.1
68.8
73.3
Fat loss
4.1
12.1
12.6
Moisture loss
14.2
16.2
17.1
Total cooking loss . .
25.0
21.6
18.3
28.3
29.7
22.6
Weight of inedible
cooked portion. . .
20.3
17.6
20.0
14.3
14.9
17.4
Weight of cooked
meat
51.4
58.1
59.0
56.7
54.0
55.8
Weight of drippings.
1.0
8.9
17.5
16.3
Weight of cooked
meat and drip-
pings . .
52.4
67.9
74.2
70.3
TABLE 37
COST OF EDIBLE MEAT FOR DIFFERENT CLASSES OF POULTRY (Lowe and Fernon)
Live
weight
average,
pounds
Dressed
weight
average,
pounds
Cost per
pound
dressed
weight
Cost per
pound
cooked
meat
Cost per
pound
edible
meat plus
drippings
Broilers
Fryers
Roasters
1.87
2.95
4 51
1.67
2.66
4 01
s$0.40
0.34
30
$1.090
.778
639
$1.070
.778
550
Hens
5 03
4 63
31
738
567
Capons
7.38
6.65
0.43
.900
.688
uncovered for the last 15 minutes of cooking and the heat increased to
brown the roasts. In the covered pans used in these experiments, very little
browning occurred while the roasts were covered.
Methods and cooking temperatures. In roasting poultry, one is con-
fronted with the problem of cooking tender and less tender muscles at the
same time. As a result, when the breast is at its prime, the thigh and leg
ROASTING OF POULTRY 247
muscles may be slightly tough and, vice versa, when the thigh and leg are
cooked sufficiently to soften the connective tissue, the breast is past its prime
and is becoming dry.
Another problem in cooking poultry is the skin. If it is moist and tender,
the appearance is less attractive because it is not so brown. When the skin
is not consumed this point is not important.
The degree of fatness and its distribution, the degree of post-mortem
changes or ripening, the age, and the size may affect the cooking time and
losses of roasters. In addition, breed, sex, and the feed the bird has received
may have some effect on these factors. Hence, for fair experimental tests
the cuts should be paired. To do this Lowe and Keltner divided roasting
chickens into halves, the halves being tested one against the other to
determine the effect of the cooking temperature, covering the pan, and
basting on cooking losses, cooking time, and palatability of the meat. They
found the cooking losses were practically the same for halves cooked at
125C. (about 250F.) and at 175C. (about 350F.), but the cooking
time at the lower temperature was more than twice as long as at the
higher temperature. The differences in palatability scores for the breast
and thigh meat cooked at the two temperatures were practically negligible,
with the exception that the breast scored higher in juiciness at the higher
temperature, which was probably related to the shorter cooking time. One
drawback in cooking halves of birds was the tendency for the muscles of
the breast to separate and draw back, which is of course not encountered
in roasting the whole bird. In all these tests the half of chicken was re-
moved from the oven when the interior temperature of the thigh was
85C. (185F.).
If a searing instead of a constant temperature method is desired, cooking
the roast uncovered for 20 minutes at 200-230C. (about 395-450F.)
and then lowering the temperature to 125C. for the remainder of the
cooking period produces a juicy roast. Covering for the last 20 or 30 min-
utes of cooking increases the tenderness of the skin, as the confined steam
moistens the skin.
In tests of the searing and constant temperature methods for cooking
turkeys, in an uncovered pan and basting the turkey every half hour, the
constant temperature of 150C. (about 300F.) has in general proved
very satisfactory, the meat being tender and very juicy.
Covered and uncovered pans. Lowe and Keltner cooked halves of 22
birds covered, the other halves uncovered. All were cooked at a constant
oven temperature of 150C. and until the interior temperature of the
thigh reached 85 C. The cooking time was approximately twice as long for
uncovered as for covered halves. The total and volatile cooking losses were
greater for the uncovered halves, but the drippings were greater for covered
halves. The scores showed that in aroma, flavor, and juiciness the breast
of the uncovered halves was more desirable than the breast of the covered
248 MEAT
halves. No preference for the thigh was shown for either covered or un-
covered halves.
Covering the birds for the last 20 minutes of the cooking period short-
ened the cooking time, decreased the cooking losses, and increased the
tenderness and palatability of the skin but not of the meat. The majority
of the scorers preferred the uncovered halves.
Interior temperatures for cooking poultry. The insertion of thermometers
into muscles of chicken in early tests was not satisfactory, as the ther-
mometer and bulbs were too large. However, it was found that the larger
thermometers could be used successfully by inserting them into the stuffing,
either through the front or rear cavities of the fowl. For turkeys and geese
the thicker part of the stuffing is towards the rear of the carcass; hence it
was preferable to insert the thermometer at the rear.
Lowe and Keltner used in their study a small light thermometer with a
very short, small bulb. Placing the bulb of the thermometer into the thickest
portion of the thigh muscles and cooking the chicken until a temperature
of 85 C. was reached proved satisfactory. The most desirable temperature
to which the breast muscles should be cooked has not been determined.
Since the breast muscles tended to separate when half of a bird was cooked,
thermometers were not used successfully in the breast. However, in the
preliminary studies the temperature of the breast was usually 2 to 4
higher than that of the thigh.
Evidently the meat of large fowls is juicier if the interior temperature
of the stuffing is lower than for small fowls. This is probably due to their
size, the large quantity of stuffing that they hold increasing the distance
to the middle of the stuffing.
When chickens were roasted until the interior temperature of the stuffing
reached 80 to 83C., the meat was desirable; but, when cooked to 85C,
the breast of some birds was dry, the drippings and particularly their
moisture content increasing rapidly in the last few minutes of cooking.
This might indicate that for some birds, depending somewhat upon degree
of ripening and other factors, this is a critical temperature. As this point
is reached or exceeded, the tendency for the meat of the chicken is to
become dry and the drippings loss to increase.
For turkeys weighing 16 to 20 pounds after stuffing, an interior tempera-
ture of 75 to 82C. of the stuffing resulted in juicy meat. But for turkeys
weighing 25 to 30 pounds after stuffing a lower temperature gives better
results. The type of stuffing used may make some difference in the juiciness
of the meat and the cooking losses. Lowe and Keltner found that stuffing
made from 1 -day-old bread, 100 grams, butter 50 grams, and salt 2 grams,
but without the addition of liquid, absorbed an average moisture content
of 41.5 per cent. The amount of moisture absorbed varied from 14.6 to
78.1 per cent.
The above results and observations in cooking of poultry suggest that
poultry may lose moisture rapidly after a certain temperature is reached,
ROASTING OF POULTRY
249
with the result that the meat becomes quite dry. This loss of moisture
seems to occur most rapidly at a temperature around 83 to 85C. Some
meats may become dry more readily within a short range of temperature
than others. Ostwald states that "Pork can be distinguished from other
meats by the fact that its water holding capacity suffers the least change
when cooked or dried." The kind of food the bird has received may in-
fluence the juiciness to a certain degree.
Basting. Lowe and Keltner found that basting shortened the cooking
period, but did not appreciably affect the cooking losses. Butter was used
for basting. The salt was removed by washing, the butter was then melted,
and the curd allowed to settle. The half of chicken was basted before
putting in the oven, at the end of 30, and at the end of 60 minutes, a total
of 20 grams of butter being used. Basting increased the desirability of the
lean meat of both the thigh and breast.
Time of cooking. Roasters weighing 4 to 5 pounds, dressed weight, re-
quire about 35 minutes per pound to cook by the searing method. If estimate
is based on the stuffed weight, about 30 minutes per pound is necessary.
But considerable variation may be expected, larger roasters requiring a
shorter and smaller ones a longer time. For the constant oven temperature,
150C. (about 300F. ), approximately the same time will be required
as for the searing method though again considerable variation may be
expected.
Table 38, based on laboratory results, gives approximate time for roast-
ing turkey at 150C. Variation from this time will of course be found. The
time given is for uncovered birds. A. shorter time will be required when
the roast is covered.
TABLE 38
APPROXIMATE TIME FOR COOKING TURKEY
Turkey
Weight of
stuffed bird
in pounds
Average total
cooking time
in hours
Average time
per pound
in minutes
Small . . .
6 to 10
3 to 3>^
20 to 25
Medium
10 to 16
^/2 tO 4>^
18 to 20
Large
18 to 23
4> to 6
16 to 18
Effect of feed on fat distribution. Maw has investigated the effect of
cereals, yellow corn, wheat, oats, and barley on the amount and nature
of the fat deposited in different parts of the body (flesh, abdominal fat, ex-
ternal fat, and skin). Flesh as used was composed of the breast and leg
muscles with external fat stripped clean. The wheat gave an excellent
external appearance as it produced an external layer of fat over the carcass
250
MEAT
but relatively little fat distributed through the flesh. Table 39 gives his
results :
TABLE 39
DISTRIBUTION OF FAT IN THE BODY (Maw)
Cereal
Percentage
total fat
Fat in
flesh
Fat in
skin
Abdominal
fat
Corn
13 4
30
55
15
Barley..
12.1
26
59
15
Oats
12 1
22
57
21
Wheat
12 9
20
60
20
Maw states that the fat laid down in the carcass is replacing the moisture.
This fat in the cooked bird influences the apparent moistness of the flesh.
The palatability tests indicated the corn-fed birds appeared the most moist,
with the best flavor. The barley-fed meat was nearly like the corn-fed ;
whereas the oat-fed and wheat-fed meats were the poorest in quality, the
wheat-fed apparently being the driest and poorest in flavor. These birds
were roasted at a constant temperature of 375 F.
LITERATURE CITED AND REFERENCES
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Hoagland, R. Formation of Hematoporphyrin in Ox Muscle During Autolysis.
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MEAT 253
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MEAT
Experiment 37.
To determine the effect on muscle fiber and connective tissue of cooking by
dry heat.
Scrape a piece of lean meat with the dull edge of a knife until the connective
tissue and fiber are separated. Save a portion of the fiber and connective tissue
to use in Experiment 38. Form in small balls and cook in a hot frying pan.
What is the effect of dry heat on the connective tissue? On the fiber? Which
is affected the most?
Experiment 38.
To determine the effect on muscle fiber and connective tissue of cooking by
moist heat.
254 MEAT
1. Cook a portion of the fiber and the connective tissue in boiling water.
If the water evaporates, add boiling water.
2. Cook a portion of the muscle fiber and the connective tissue in water.
Do not let the temperature of the water go above 85C. Compare the texture
of the fiber and the connective tissue from Experiment 37 with Experiment 38,
1 and 2. What temperature would be best to cook a piece of meat containing
a great deal of connective tissue to soften the connective tissue, yet keep the
muscle fibers tender?
Texture
Time to cook
Fibers
Connective tissue
Fibers
Connective tissue
Results and conclusions.
Beef Roasts
Experiment 39.
To determine the effect on beef roasts of cooking to different stages of
doneness.
1. Preparation. Weigh the roast. Wipe with a damp cloth. A tracing may
be made of the cut surfaces of the meat. Determine the place and depth for
insertion of the thermometer. Measure the width of the roast. The thermometer
is inserted half way. See Fig. 23, p. 225. To determine the depth to insert the
thermometer, measure the distance on the two cut surfaces as indicated in
Fig. 25, diagram Z), p. 234. The distance should be the diameter of a circle, so
that the bulb of the thermometer can be inserted equally distant from the top,
the chine bone, and the bottom of the roast. If the depth on one cut surface is
4 inches and on the other 4^ inches, use an average of these two, or 4j4
inches, for the distance represented by the diameter of the circle. Measure
up from the center of the thermometer bulb 2 l /% inches on the stem and
insert to this depth in the roast. The incision for the thermometer should be
made with a very narrow knife blade, about l /4 inch in width, or a skewer
so that the meat will fit tightly around the thermometer. For a rolled roast
find the radius (one-half of the diameter) and insert the center of ther-
mometer bulb to this depth in the middle between the two ends of the roast.
Weigh the thermometer and the cooking pan. Use an open pan. A common,
sheet-iron pan is suitable for roasting. A standing-rib roast rests on the chine
bone and rib ends, which keeps the roast above the drippings. See Fig. 23.
A rolled roast is laid on a rack with the fat side up. No water or seasoning
are added. Record the inner temperature of the roast and oven at definite
intervals, 10, 15, or 20 minutes, during the cooking period. Cook by one of
the following methods. If paired roasts are used, one may be cooked by a
searing, the other by a constant temperature method.
BEEF ROASTS
Searing method. For experimental comparisons sear the roast for 20 minutes
at 250-275C. (about 480-525F.) and transfer at the end of 20 minutes
to an oven at 125C. (about 255F.). For a searing method suitable for the
home, sear at 220C. (about 425F.) for 20 minutes, then set the regulator
for 125C. (about 255F.).
Constant temperature method. Place the roast in an oven with temperature
of 150C. (about 300F.).
Cook the roast until the thermometer registers 55C. (131F.). Note
exterior appearance on removal from the oven. Note and record any change
in interior temperature of the roast. When the temperature is constant, weigh
the roast. Weigh pan and drippings. Cut the roast through the center. Describe
its condition, its color, and uniformity of color throughout the roast, its sheen
and amount of juice on the surface. Score for tenderness, flavor, and juiciness.
If the volatile and drippings losses in the oven are to be determined sepa-
rately from those after removal from the oven, the roast is weighed at the
time it is removed from the oven and transferred to a weighed platter. When
the maximum temperature is reached, the roast is reweighed to determine
the volatile loss during the interval after removal from the oven and attain-
ment of maximum interior temperature. The platter is reweighed to determine
the drippings collected outside the oven.
Samples for scoring. For scoring cut off the outside slice and lay aside, as
the browned part will affect the flavor. Cut as many slices as there are people
to score. Cut from the same position in each roast and be sure that the same
person gets slice 1 from all roasts, etc. If slices are very large they may be
divided, but the same portion of each muscle should be given to the same
scorer.
Determine the percentage lost during cooking, the dripping loss and the vola-
tile loss. Plot on graph paper the rise in inner temperature of the roast, during
cooking and after removal from the oven. The weight of the bones and the
per cent edible may also be determined.- Calculate the time per pound required
for cooking.
2. Repeat 1, but do not remove the roast from the oven until the inner
temperature is 63C. (145F.). If desired the roast can be removed when the
interior temperature reaches 61C. Compare with 1 for color, juiciness, tender-
ness, flavor, loss of weight, and rise of temperature after removal from the
oven.
3. Repeat 1, but do not remove from the oven until the inner temperature
is 75C. Compare with 1 and 2.
The following headings are suggested for records and may be used in all the
following experiments, unless otherwise suggested. Where several roasts are to
be cooked it is better to have mimeographed sheets for making records.
Weight before
cooking
Weight
after
cooking,
grams
Total
loss,
grams
Fat
loss,
grams
Volatile
loss,
grams
Total
loss,
per cent
Fat
loss,
per cent
grams
pounds
256
X -<--.. --K <-*
MEAT
Interior
Time after
Volatile
loss,
per cent
temperature
when
removed
from oven,
Maximum
temperature
reached,
removal
from oven to
obtain
maximum
Total
time of
cooking,
minutes
Time of
cooking
per pound,
minutes
c.
temperature
Weight of
edible
cooked
portion,
grams
Edible
portion,
per cent
Color
Tender-
ness
Juici-
ness
exterior
interior
Results and conclusions.
Experiment 40.
To determine the rate of temperature rise near the surface of the roast as
compared with the center of the roast.
1. Repeat Experiment 39,1, but place a second thermometer y 2 inch from
the surface of the roast. Take the readings on both thermometers every 10
minutes. Remove from the oven when the temperature at the center is 55C.
Continue to record the changes in temperature. What differences do you note
in the changes of temperature in the two portions of the roast? Plot on graph
paper the rise in temperature in the two portions of the roast. Compute losses
and make records as suggested under Experiment 39.
Experiment 41.
To determine the effect of cooking at different temperatures on standing
beef rib roasts.
Three pairs of two-rib roasts can be obtained from one carcass, the pairs
consisting of ribs 11 and 12, 9 and 10, and 7 and 8. These pairs can be used
to compare the cooking losses, the exterior and interior color, the juiciness,
tenderness, and flavor of roasts cooked at various temperatures. See the
following suggestions. Cook the roasts to the same interior temperature, 63C.
(If desired either 55C. or 75C. may be used.)
1. a. Use a constant oven temperature of 125C. for cooking one roast of
the pair.
b. Cook the other roast at a constant temperature of 225C.
2. Compare the effect of constant oven temperatures of 125C. and 175C.
3. Repeat (2) but compare 125C. and 150C.
4. Repeat (2) but compare 150C. and 175C.
LAMB, PORK, AND VEAL ROASTS 257
5. Repeat (2) but compare 150C. and 225C.
6. Use the experimental searing method (20 minutes at 250-275C., then
transfer the roast to a second oven at 125C.) with a constant temperature
of 125C.
7. Repeat (6) but compare the searing method and a constant temperature
of 150C.
The lower searing temperature may be substituted for the experimental
searing method in any of the above suggestions. In addition the experimental
searing method may be used with temperatures of 150C. and 175C. to com-
plete the cooking.
If rolled instead of standing rib roasts are used, they should be placed on
racks to keep them above the drippings. Compute losses and make records as
suggested under Experiment 39.
What is the interior temperature of a roast which is rare? Of a medium
well-done roast? Of a well-done roast? In each case what was the number of
minutes per pound required for roasting? What is the effect of increasing the
size of the roast on the time required per pound? How much did the inner
temperature of roasts rise after removal from the oven? What factors cause
variations in this rise in temperature? If a rare roast is to be served immedi-
ately, at what temperature would you remove it from the oven? Is the rate of
increase of inner temperature of the different roasts constant?
Lamb, Pork, and Veal Roasts
Experiment 42.
To determine the effect on roasts of cooking at different temperatures.
Use roasts of lamb, pork, and veal, but if possible the roasts should be
paired; that is, use the same cuts from the right and left sides of the same
carcass. Make tracings of cut surfaces of the roasts. Make a record of width.
Determine the total, the dripping, and the volatile losses. Calculate the time
of cooking per pound. Find the rise of inner temperature after removal from
the oven. Compare the roasts for juiciness, flavor, and tenderness. Record the
inner temperature of roasts and ovens at the same intervals used in Experi-
ment 29 and plot on graph paper. Make records as suggested under Experi-
ment 39.
For all the following roasts the bulb of the thermometer should be placed
in the center of the thickest portion of the roast, which is not necessarily the
center of the piece of meat. If a loin roast of pork is used the thermometer
bulb should be in the center of the large muscle along the backbone.
A. Lamb.
Preparation. Weigh the roast. Wipe with a damp cloth. Insert the ther-
mometer bulb into the thickest portion of the leg. Use two rulers held at right
angles to each other to determine the depth of inserting the thermometer bulb.
Place the roast on a rack in a weighed, open pan so the skin side or fell side
is down if a leg of lamb is used, and up if a shoulder roast is used. Record
the temperature of roast and place in oven without addition of water or
seasonings. Cook to an interior temperature of 75C.
1. Use the constant 150C. oven temperature. Cook one leg of lamb with
the fell removed but leave the fell on the other leg of this pair.
258 MEAT
2. For paired roasts use any of the cooking temperatures suggested under
Experiment 41.
B. Pork loin.
Preparation. Weigh the roasts. Insert the thermometer in the same manner
as for beef-rib roasts. Place the roast with fat side up on a rack in a weighed
pan. Cook to an interior temperature of 84C.
Searing method. Because of the long time required to cook pork roasts, a
temperature of 150C. was used for the temperature of cooking in the second
oven after searing at 250-255C. for 20 minutes with the experimental
searing method.
1. For paired roasts use any of the cooking temperatures suggested under
Experiment 41, but use the higher cooking temperature with the experimental
searing method.
C. Veal.
Preparation. Prepare in the same manner as other roasts. Place on a rack
in an open pan. The cut used for roasting in the Cooperative Meat Investiga-
tions is a section of the thigh about 4 inches wide cut through the femur just
inside the end of the enlarged joint. Cook to an interior temperature of 71C.
1. For paired roasts use any of the cooking temperatures suggested under
Experiment 41.
Experiment 43.
To determine the effect on roasts of lamb, pork, and veal of cooking to
different stages of doneness.
Follow the directions under Experiment 42 and cook roasts of veal, lamb,
and pork. Cook by the constant temperature (150C.) method and vary the
interior temperatures to which the roasts are cooked as follows:
Lamb: 71, 75-76, and 83C.
Pork: 78, 83-84, and 88C.
Veal: 71, 75, and 80C.
Steaks and Chops
Experiment 44.
Steaks.
To determine the effect upon steaks of cooking by different methods and to
different interior temperatures.
Rib, porterhouse, sirloin, or round steak may be used. Steaks for compara-
tive tests by the Cooperative Meat Investigators are cut 2 inches thick. Steaks
1 to \ l /\ inches in thickness are satisfactory for class work.
Preparation. Weigh the steak. Make a tracing of the cut surfaces. Measure
the thickness. Insert a weighed thermometer, so that the bulb is midway, i.e.,
Y-2. inch from the top and from the bottom of a steak 1 inch thick. A right-
angle thermometer should be used for steaks to be pan-broiled, but either a
tube or right angle may be used for broiled steaks. Steaks may be turned at
regular intervals or only once. If turned only once, Cline suggests turning
STEAKS AND CHOPS 259
the steak when about three-fifths of the expected temperature rise has oc-
curred. If the temperature of the steak is 10 and it is to be cooked to an
interior temperature of 60, the temperature rise will be 50, and three-fifths
of 50 equals 30. Thus the steak will be turned when the inner temperature
is about 40C. To turn, stick a fork into the flank muscle, connective tissue,
or firm fat and not into one of the principal muscles.
Keep a record of the interior temperature of the steaks at regular intervals.
Note and record the temperature rise after cooking is stopped. Plot on graph
paper. Record the time for cooking and minutes seared on each side (if searing
is used). Compute the total, the volatile, and drippings losses.
Compare the steaks for exterior appearance, interior color, juiciness, flavor,
and tenderness. In preparing samples for testing, be sure the scorer gets the
same slice from each steak.
Cook all steaks to an interior temperature of 61 C.
A. Method of cooking.
1. Broiled. Weigh the broiling pan and rack. Place pan so that the top of
the steak will be about 4 inches below the flame. A fireless cooker ther-
mometer may be placed at the left front on the first two rods. Heat the broiler
pan and rack until the fireless cooker thermometer registers about 175C.
Place steak on rods in the center of the pan with thermometer at the right-
hand side and broil until the desired temperature for turning is reached. Turn
so that the thermometer is still at the right-hand side. Turn the thermometer
so the reading scale is up. Remove when the desired interior temperature is
reached. Note temperature rise. When the maximum temperature is reached,
weigh the steak and the broiler pan and drippings.
For variation in temperature of broiled steaks, lower or raise the top of
the steak farther from or nearer to the flame.
2. Pan broil. Sear on each side in a hot skillet. Turn. Lower heat and cook
slowly until the temperature for turning is reached. Turn and cook until the
desired interior temperature is reached. Remove and follow directions under (1).
3. Pan broil. Repeat (2) but use a constant temperature for cooking.
B. Varying the interior temperature to which steak is cooked.
1. Use the same method for cooking all steaks. Follow directions under A
and cook until the interior temperature reaches rare, 55 to 57C.
2. Repeat (1) but cook medium well done, 61C.
3. Repeat (1) but cook well done, 71C.
C. Thickness of the steak.
Cook by the same method and to the interior temperature decided upon by
the class. Compare the cooking losses and time of cooking.
1. Use a steak ^2 inch thick. (Cannot use thermometer.)
2. Repeat (1) but use a 1-inch thick steak.
3. Repeat (1) but use a steak cut \ l /2 inches thick.
Chops.
Repeat any of the above experiments using chops of pork, lamb, or veal.
Cook pork chops to an interior temperature of 80C., lamb to 75C., and
veal to 71C.
260 MEAT
Less Tender Cuts
Experiment 45.
To determine the effect of various factors in cooking less tender cuts of
meat.
Braising. Cuts. Use paired cuts. Cuts from the neck, flank, rump, round,
or particular muscles from the round such as the semitendinosus may be used.
One piece is cut from the right, and a second piece of the same size and
from the same position from the left side of the carcass. Pieces weighing
about 1 to lj/2 pounds are satisfactory for class work.
Preparation. Weigh the pieces. Each member of the class cooks a pair of cuts.
Everything, as nearly as possible, should be standardized, except the variable
being tested. For example, if the effect of pounding is to be determined, both
pieces may be seared but only one should be pounded.
Add 2 grams of salt per pound of meat. Add l /4 cup of liquid per pound
and more if necessary, but keep a record of the amount added. With larger
pieces of meat a relatively smaller proportion of liquid may be added. If
necessary to add water, have it boiling.
Use covered containers, of a size suitable for the pieces of meat being
cooked, such as casseroles, Dutch ovens, skillets, etc. For some experiments
both pieces of the pair may be cooked in the same container, one or both
pieces being marked with a metal tag or with tooth picks. For other tests
separate utensils will need to be used for each piece of meat.
Determine only the total cooking losses. Compare the juiciness, flavor,
tenderness, and slicability of the meat.
The following suggestions are offered for tests:
1. Pounded vs. not pounded.
2. Floured vs. not floured (neither piece pounded).
3. Floured vs. not floured (both pieces pounded).
4. Seared vs. not seared (neither pounded nor floured).
5. Seared vs. not seared (both pounded and floured).
6. Covered vs. uncovered.
7. Lower (simmer) vs. higher temperature (boiling over flame).
8. Lower vs. higher temperature (in oven).
9. Add tomato juice as liquid to one piece, an equal quantity of water to
the other.
10. Repeat (9) but substitute sour cream for the tomato juice.
11. Remove one piece when the interior temperature reaches 75C., the
other when the inner temperature reaches 85C.
12. Remove one piece when the interior temperature reaches 85C., the
other at 95C.
Many combinations of the above suggestions and other combinations not
mentioned may be tried.
Cooking Meat in Water
Experiment 46.
To determine the effect of temperature of the water upon the palatability of
the meat
GROUND MEAT 261
Stews. Use neck, heel of round, or any of the less tender cuts. The meat
is cut into cubes of the size desired, using equal quantities from each side of
the carcass. Cook in covered utensils. The amount of water added is usually
just sufficient to cover the meat. This will have to be determined in connec-
tion with the utensils used for the stew. At the start try using l /2 cup of
liquid to each pound of meat. For boiling temperatures this should be doubled.
Use 2 grams of salt per pound of meat. For stews the meat is usually pre-
pared in one of three ways, (a) Brown stew. The meat is seasoned and
seared in fat before it is added to the boiling liquid. The meat may be floured
before it is seared. The flour browns more readily and adds color to the
liquid, (b) The meat is added directly without searing to the boiling liquid,
(c) The meat, without being seared, is added to the cold liquid and heated
slowly to the desired temperature. If vegetables are used with the stew, they
are added so that they will just become tender before the stew is served. The
broth of the stew may be thickened slightly.
1. Brown stew. Dredge the meat with flour. Add salt. Sear in hot fat.
Add the seared meat to the boiling water. Cook one stew at simmering
(85-90C., 185-194F.) temperature, the other at boiling. Add boiling water
to either as needed, but the amount of water when served should not cover
the meat or meat and vegetables when served.
2. Repeat (1) but add the unseared meat to the boiling water.
3. Repeat (1) but add the unseared meat to cold water. Heat slowly to sim-
mering and boiling temperatures.
Compare the meat from the various stews for flavor, juiciness, slicability
(if pieces are large enough to slice), stringiness, tenderness, and time of
cooking.
Broth
Experiment 47.
To determine the best method of making broth.
Use l /2 pound of meat for each experiment and 1 pint of water. Add water
as necessary to keep the volume constant.
1. Cook the meat in one piece. Start in cold water and heat to 85C. Cook
until tender, keeping the temperature 85C.
2. Repeat 1, but cut the meat in 1-inch cubes.
3. Repeat 1, but grind the meat.
4. Repeat 2, but start in boiling water and cook at boiling temperature.
5. Repeat 2, but sear the meat before adding to the water. What are the
differences in the broth in each case? How is a clear broth prepared? Strain
some of the above broths. To another add a beaten egg white, heat, then strain.
Ground Meat
Experiment 48.
To determine the effect of various factors upon the palatability of ground
meat.
262
MEAT
Meat loaf.
Recipe:
Ground lean beef
y pound
113 grams
Butter
]/2 tablespoon
7 grams
Egg, beaten
/4
12 grams
Milk
y* cup
61 grams
Salt
y^ teaspoon
1 gram
Ground suet 14 grams
Bread crumbs 25 grams
Pepper yfa teaspoon
Mix the ingredients lightly with a fork. The meat loaf may be baked in
individual casseroles or even in pyrex custard cups the same weight being put
in each dish. Bake in the oven, putting a right-angle thermometer into each
sample, the thermometer being suspended by the horizontal arm on a rack
above the meat loaf. Ground meat from the retail market may be used for A
and B and the suet omitted.
A. The temperature to which the meat loaf is cooked.
1. Bake in an oven at 160C. (about 325F.) until the interior temperature
reaches 75C.
2. Repeat (1) but remove from the oven at 80C.
3. Repeat (1) but remove from the oven at 85C.
4. Repeat (1) but remove from the oven at 90C.
B. The temperature of the oven.
Bake to the interior temperature found best under A.
1. Bake at 150C. (about 300F.).
2. Bake at 160C. (about 325F.).
3. Bake at 175C. (about 350F.).
4. Bake at 185C. (about 365F.).
C. Effect of fineness of grinding of the meat.
Bake to interior and at oven temperatures found best under A and B.
1. Grind meat once, using a coarse knife in the grinder.
2. Grind meat once with a medium knife.
3. Grind meat once with a fine knife.
4. Repeat (2), putting meat through the grinder 4 times.
5. Repeat (3), putting meat through the grinder 4 times.
D. The effect of increasing the fat.
Bake to interior and at oven temperatures found best under A and B.
Grind to the degree of fineness found best under C.
1. Add 7 grams of ground suet. (If desired butter may be used instead of
the suet.)
2. Add 14 grams of ground suet.
3. Add 21 grams of ground suet.
4. Add 28 grams of ground suet.
Compare the flavor, moistness, and texture of the various meat loaves.
HAM 263
Hamburger.
Recipe :
Ground beef ^ pound 113 grams
Egg y^ 12 grams
Salt ^4 teaspoon 1 gram
Pepper % teaspoon
Mix the ingredients together with a fork. For uniformity of temperature
the hamburger may be baked in custard cups according to directions given under
meat loaf. It may also be made into patties and seared, then cooked slowly as
is the usual practice.
1. Repeat section A under meat loaf.
2. Repeat section C under meat loaf.
Cured Meats
Ham
Experiment 49.
To determine the effect of various factors affecting the palatability of ham.
Hams may be secured with a light or a heavy salt cure. The former do not
need to be soaked before cooking; the latter may be improved by soaking.
Preparation. For hams with a light salt cure, scrub with a brush. Dry, then
weigh. Insert thermometer so that the center of the bulb is at the center of
the thickest portion of the ham, with rind or fat side up. To determine the
depth for inserting the thermometer use two rulers at right angles to each
other. Or with a steel skewer pierce the rind or fat side, running the skewer
point just through the ham. Withdraw and measure the depth the skewer was
in the ham. The thermometer is to be inserted half this distance. If the rind
has not been removed, it will need to be cut away with scissors or a knife so
that the thermometer can be inserted. Use hams of about the same weight for
all the tests.
For hams with a heavy salt cure, soak, keeping the time of soaking and the
amount of water used standardized. Soak over night using a quart of water
to each pound of ham. Remove from the soaking water and drain 10 minutes.
Weigh and proceed as for non-soaked hams.
Record the temperature of ham and oven every 10 minutes for the first
30 minutes, then every 20 or 30 minutes. For hams from which the rind has
not been removed, remove the rind after the ham comes from the oven. If to be
scored hot, cut as soon as the maximum temperature is reached. If to be
scored cold, store after removing rind.
A. Baked ham.
Place the ham skin side up on a rack in an open weighed pan. Add no water
or seasoning.
1. Bake in an oven at 125C. (about 255F.) until an interior temperature
of 70C. is reached.
2. Repeat (1) but cook to an interior temperature of 75C.
3. Repeat (2) but cook to an interior temperature of 80C.
264 MEAT
4. Repeat (1) but have the oven temperature 150C. (about 300F.).
B. Boiled ham.
Use kettles with covers, ham boilers, or boilers of such size that the water
will cover the ham. The ham is placed on a rack, rind or fat side up. Use
an ordinary laboratory thermometer to take the temperature of the water.
Add 1 quart of water per pound of ham. Occasionally add water at the same
temperature as water in which ham is cooked to replace that lost by evapora-
tion.
1. Let simmer in water at 83C. until an inner temperature of 75C. is
reached. Or, if preferred, use the interior temperature preferred with baked
ham. Remove from the water. Drain. Weigh. Keep over night in the re-
frigerator.
2. Repeat (1) but let the ham cool over night in the liquor in which it was
cooked. Let the kettle remain in the room so that the liquid will cool to room
temperature. Remove from the liquid. Drain 10 minutes and weigh. Place in
the refrigerator to be scored with hams from (1) and (3).
3. Repeat (1) but put the kettle or boiler in the refrigerator over night,
letting the ham cool in the liquor in which it was cooked. Remove from liquid.
Drain 10 minutes, and then weigh.
4. Repeat (1) but keep the temperature of the water at 87C.
5. Repeat (1) but keep the water at 78C.
Bacon
Experiment 50.
To determine the effect on the flavor and the losses of bacon by cooking
at different temperatures and to different stages of doneness.
Weigh the bacon before and after cooking to determine the percentage
lost during cooking. The difference in weight of the uncooked and cooked
bacon is the total cooking loss. The weight of the fat in the cooking utensil
is the approximate fat loss.
Have the bacon sliced or cut on a slicing machine 3/32 inch thick. Make a
tracing of slices if desired.
1. Place the slices of bacon on a rack y 2 inch above the bottom of an open
pan. Cook in an oven at 160C. (about 320F.) for 18 minutes. Do not turn.
2. Place the weighed slices of bacon so that they lie flat and full length
in a cold, heavy iron or aluminum skillet. (With a 9-inch skillet 3 slices of
bacon will usually lie flat and full length.) Place over a slow fire and cook
slowly until a uniform brown in color. It should be medium well done or crisp
but not brittle. Turn the bacon frequently and in such a manner that it is
cooked uniformly. Often the center, if the skillet is hot, of the slice of bacon
is done while the ends are not.
3. Place the weighed slices of bacon so that they will lie flat and full length
in a hot, heavy iron or aluminum skillet. Cook rapidly at a high temperature
until a uniform brown in color. Turn the bacon frequently and in such a man-
ner that it is cooked uniformly.
4. Repeat 2, but cook the bacon until it is very crisp and well done or brittle.
Compare the cooking losses and flavor with 1 and 2.
Which method of cooking gives the best-flavored bacon? Which method
SUGGESTIONS FOR ADDITIONAL EXPERIMENTS 265
causes the fat to smoke or burn? Does the bacon taste of burned fat? Which
method causes the bacon to curl the most? Which method gives the most
evenly cooked product? Compare the flavor, the cooking losses, and the cost
of the cooked bacon, cooked only until crisp and that cooked until brittle.
Weight of
Weight of
Total
uncooked
bacon,
cooked
bacon,
cooking
loss,
Fat loss,
per cent
Straight
or curled
Color
Flavor
grams
grams
per cent
Results and conclusions.
Experiment 51.
To compare the flavor and cooking losses of different brands of bacon.
Cook different grades and brands of bacon in the oven at 160C., see Ex-
periment 50,1. The different bacons may be scored before and after cooking
for the color and uniformity of color of lean and fat, for the percentage of
fat and lean, the distribution of the lean and the fat, and for texture. The
cooked bacon may be scored for color, the clearness of the fat, the percentage
and distribution of fat and lean, the crispness, and the flavor.
Brand of or
grade of
bacon
Uncooked
weight,
grams
Cooked
weight,
grams
Total
cooking
loss,
per cent
Fat
loss,
per cent
Straight
or curled
Flavor
Results and conclusions.
Suggestions for Additional Experiments with Meats
1. Determine the effect on total cooking loss of cooking roasts in a covered
and uncovered pan.
2. Determine the effect of salting on cooking losses of chops, steaks, and
roasts.
CHAPTER VIII
EMULSIONS
Some substances like alcohol and water are miscible in all proportions,
i.e., they mix intimately however small or large the proportions used,
whereas other substances like oil and water are not miscible.
When a liquid is dispersed in a second liquid with which it is non-
miscible the product is called an emulsion. The boundary surface between
these two non-miscible liquids is referred to as the liquid/liquid interface,
or the dineric interface. Most emulsions are colloidal systems in which the
dimension of the dispersed phase is greater than 0.5/x, the upper limit of
the colloidal realm. However, the stabilizing film in the concentrated
emulsions may have colloidal dimensions.
In cookery, the liquid of the emulsion may be water, milk, a weak acetic
acid solution, or some similar liquid. The fat or oil may be any fat or
oil used as a food. Mineral oils may also be used for emulsions. If emul-
sions are mentioned in connection W 7 ith food preparation, mayonnaise is
usually the one suggested first. However, all thickened gravies, sauces, and
cream soups are emulsions. Fillings for pies like chocolate cream, and
French and cooked salad dressings, may be added to the list. In many
of the batter products the fat or oil may be partially or wholly emulsified.
Forming emulsions. To form emulsions, work must be done. The
function of the work is not only to separate the dispersed phase into smaller
particles, but to increase the surface area, which gives a better opportunity
for the two phases to come in contact with each other and increases the
area for adsorption of the emulsifying agent. Stirring, beating, shaking,
grinding, or some other method may be used to disperse one of the sub-
stances.
Dispersed and continuous phases. The substance broken into small
portions is called the inside, the discontinuous, or the dispersed phase ; the
one surrounding the dispersed phase is designated as the outside, the con-
tinuous phase, or the dispersing medium. If oil and vinegar are shaken
together, French dressing is made, but after standing a few minutes the
oil and vinegar separate. This type of emulsion that lasts for a few minutes
only is sometimes called a temporary emulsion.
Emulsifiers. A permanent emulsion of pure water and pure oil can
be formed only when the proportion of oil is very small, less than 2 per
cent, and usually not more than 1 part of oil in 10,000 parts of water. For
a permanent emulsion with a high percentage of fat or oil, a third sub-
stance must be present to prevent the drops of oil or of water from
266
THE PHASE-VOLUME THEORY 267
coalescing or running together. This third substance is known as an emul-
sifying agent, an emulsifier, or a stabilizer. Its function is to form a film
around the oil or water drops and thus keep them dispersed, giving per-
manence to the system.
Classes of Emulsions
Clayton states that two very distinct classes of emulsions exist. ( 1 ) The
very dilute emulsions. These emulsions are simple emulsions, containing
only oil and water. In this class only the oil in water emulsions are known.
(2) The concentrated emulsions. The more concentrated emulsions may be
either of two types according to whether the oil or the water is the dis-
persed phase. In the ( 1 ) oil-in-water type of emulsion the drops of oil are
the dispersed or divided phase. In the (2) water-in-oil type of emulsion
the water is the dispersed phase. The factors determining the type of emul-
sion formed will be considered later.
The Theory of Emulsification
Bancroft states that the necessary conditions for forming a stable emul-
sion are that the drops of the dispersed phase shall be so small that they
will stay suspended and that there shall be a sufficiently viscous film
around each drop to keep the drops of the dispersed phase from coalescing.
Many theories have been advanced to account for the way or means by
which the emulsion is stabilized by the emulsifier. At the present time
no theory has been postulated that seems to apply universally to all emul-
sions. As Fischer suggests, probably a number of factors play a role, and
the relative importance of each varies not only in different emulsions but
in one and the same emulsion under different circumstances. Clayton in
his latest book on emulsions gives a summary of the various theories for
emulsions. Only a few will be mentioned here.
The electrical double layer. The oil globules in a pure oil and pure
water emulsion carry a negative charge. The water ionizes so that both
hydrogen and hydroxyl ions are present. The negative charge on the oil
may come from adsorption of the OH ions. These adsorbed hydroxyl ions
form a layer around the oil globules. A second layer of oppositely charged
ions forms a layer in the liquid outside the layer of negative ions. These
two layers of oppositely charged ions are known as the Helmholtz double
layer. They are not confined to emulsions but accompany all boundary
phenomena. The electric charge is a factor in all emulsions, even those
stabilized with emulsifying agents.
The phase-volume theory. If spheres of the same diameter are packed
as closely as possible, one sphere will touch 12 others and the volume the
spheres occupy is about 74 per cent of the total volume. Thus if the spheres
or drops of the dispersed phase remain rigid it is possible to disperse 74
268 EMULSIONS
parts of the dispersed phase in the continuous phase ; but if the dispersed
phase is increased to more than 74 parts of the total volume, a reversal
of the emulsion will occur. However, the dispersed phase does not remain
rigid in shape but the drops flatten out where they come in contact with
each other, nor are all the dispersed particles the same size (see Figs. 27
to 30), so that it is possible for the dispersed phase to consist of from 1 to
99 per cent of the emulsion.
Hydration theory of emulsions. Fischer and Hooker state that
hydrated colloids make the best emulsifiers. Fischer states the emulsifying
agent, by which a permanent emulsion is obtained, invariably "proves to be
a hydrophilic colloid when water and oil emulsions are concerned (a
lyophilic colloid of some sort when other than aqueous mixtures are under
consideration). Put another way, oil cannot permanently be beaten into
water, but only into a colloid hydrate."
Fischer and Hooker have found albumin, casein, and gelatin to be good
emulsifying agents. Casein when not hydrated, i.e., at its isoelectric point,
is a poor emulsifying agent, but hydrated casein, i.e., acid or alkali casein
is a good emulsifying agent.
Fischer states that all permanent emulsions can be explained on the basis
of hydrated or lyated colloids. He says that when water changes to a
colloid hydrate, its physical constants change ; and these include, among
others, surface tension, viscosity, and adsorption. The treatment of the
colloid, such as freezing or heating, or the addition of substances which
alter the water-holding capacity of the colloid may crack the emulsion or
lessen its emulsifying ability.
Interfacial films. Clayton in discussing "Foods as Colloid Systems"
describes interfacial films as follows: "As early as 1840, Ascherson ob-
served 'that coagulation in form of a membrane occurs inevitably and
instantaneously when albumin comes into contact with a liquid fat.' Any
solute which lowers the interfacial tension between oil and w r ater will
necessarily accumulate at that interface, and in the case of certain proteins,
notably albumen, the act of adsorption leads to a change in the physical
character of the emulsifying agent, this being 'precipitated' as a fibrous or
membrane-fibrous solid, no longer soluble in its original solvent. The ex-
istence of such interfacial membranes was verified by Ramsden and other
investigators."
In reading the various theories of emulsion one is impressed with the
similarity of many factors.
Oriented wedge theory. This theory for the manner in which emul-
sions are stabilized has been developed from the work of Langmuir and of
Harkins. It is based upon the concept that the molecules of the emulsifier
orient themselves in the interface between the dispersed and continuous
phases, forming a wedge, the curvature of which determines the size of the
dispersed phase. Fuller accounts may be found in Clayton's book and in
the articles of the authorities mentioned above.
THE TYPE OF EMULSION FORMED 269
Adsorbed film and interfacial tension theory. This theory has been
developed or rather extended from earlier theories. At the present time it
is probably the most universally accepted theory for the formation of emul-
sions. Bancroft stated the underlying principles, basing them upon Don-
nan's early work of interfacial tension ; but many others have extended the
interpretations. Clayton states that with this theory "emphasis is laid upon
the fact that emulsification is influenced by (1) the mass of the emulsi-
fying agent present, (2) the ease with which this agent is adsorbed at the
interfacial separating surface, and (3) the nature of the ions adsorbed by
the resultant film."
The emulsifier may be adsorbed by the water or by the oil, but it is
usually adsorbed more in one liquid than in the other and thus lowers the
interfacial tension of one liquid to a greater extent than that of the other.
If the tension of the water is lowered more than that of the oil, the water
has less tendency to form drops, flows to form a film more readily, and
becomes the continuous phase. Thus the type of emulsion formed depends
upon the nature of the emulsifying agent. The above is often worded some-
what as follows: if the emulsifying agent is more soluble in water than in
the oil the water becomes the continuous phase, or if the emulsifying agent
is wetted more by the water than by the oil, the water becomes the con-
tinuous phase. When the tension on each side of the film or the emulsifying
agent is the same no emulsion is formed. This may occur when opposing
emulsifying agents are in the mixture and the effect of each counterbalances
that of the other.
To form an emulsion the emulsifier must be adsorbed at the interfacial
surface and form a sufficiently coherent film to stabilize the emulsion.
The reversal of the emulsion depends upon the nature of the ions adsorbed
by this film. Bhatnagar stresses more than previous workers the necessity
for wetting of the adsorbed film.
The making of permanent emulsions is important for foods, cosmetics,
pharmaceutical preparations, sprays, and other products. But breaking of
emulsions is important in crude oil operations for recovery of the oil. Hence
emulsions have been investigated from many angles and it is not surprising
that no one theory applies to all types of emulsions.
The Type of Emulsion Formed
The type of emulsion formed, i.e.: (1) oil-in-water or (2) water-in-oil,
depends upon the nature of the emulsifying agent, the nature of the oil,
and the effect of electrolytes. With one emulsifier an oil-in-water emulsion
may be formed with a specific oil. Sometimes by the addition of the right
substance, usually an electrolyte, the emulsion can be reversed and changed
to a water-in-oil emulsion. Other emulsifiers with the same oil will form
water-in-oil emulsions.
Bancroft states that a hydrophilic colloid tends to make water the dis-
270 EMULSIONS
parsing phase, and a hydrophobfc colloid tends to make water the dis-
persed phase.
The potassium and sodium soaps are more soluble in water than in the
oil and form oil-in-water emulsions. Magnesium and calcium soaps are
more soluble in oil than in water and tend to form water-in-oil emulsions.
Aluminum and iron soaps are more soluble in oil than the magnesium and
calcium ones and form water-in-oil emulsions.
Bhatnagar emphasizes the influence of the electric charge of the emulsi-
fying agent upon the type of emulsion formed. He makes the following
generalization. "All emulsifying agents having an excess of negative ions
on them and wetted by water will yield oil-in-water emulsions, while
those having an excess of adsorbed positive ions and wetted by oil \vill
give water-in-oil emulsions."
Seifriz, in his work with petroleum oil emulsions stabilized with casein
solution, found that the oils with a specific gravity of 0.828 or below
form oil-in-water emulsions. When the specific gravity of the oil is greater
than 0.857 a water-in-oil emulsion is formed, and oils with specific gravity
between 0.828 and 0.857 give coarse, unstable emulsions or cannot be emul-
sified at all.
Reversal of type of emulsion. No definite rule can be given concern-
ing the reversal of emulsions. The addition of an electrolyte in definite
concentrations may stabilize some emulsions and bring about reversal of
others. Reversal of some emulsions may occur upon the addition of a
definite quantity of a hydroxide. Sometimes the addition of more of the
hydroxide will again bring about a reversal of the emulsion into the origi-
nal type. Shaking after standing may cause reversal of some emulsions.
Some ions are antagonistic to each other. Thus Clowes has shown that,
if a rancid oil is dropped from a pipette which has the end immersed
under w^ater, drops of a certain size are formed. But if the oil is dropped
into a sodium chloride solution, the drops are very much smaller. This is
probably due to the formation of sodium soaps with the rancid oil and the
lowering of the interfacial tension. If the oil is dropped into a calcium
chloride solution the interfacial tension is increased and very large oil
drops are formed, owing in this case to the formation of calcium soaps.
If both sodium and calcium are in the solution they antagonize each other
and the result obtained will depend on the concentration of each present.
Sodium and potassium are antagonistic to calcium and magnesium.
Means of determining the type of emulsion. Several ways have
been proposed to determine which of the two liquids is the continuous
phase.
The drop-dilution method may be used to determine the type of emul-
sion by the microscope. To a small portion of the emulsion placed on a
slide add a drop of water with a pin point and stir slightly. If the water
blends with the emulsion, it is an oil-in-water emulsion, but if oil blends
with the outside phase it is a water-in-oil emulsion.
SOME FOOD EMULSIFIERS 271
Another method of determining the type of emulsion is to use Sudan
III or Scharlach R, red dyes soluble in the oil but not in the water. A
small portion of the finely powdered dye is dusted over the surface of the
emulsion. If oil is the external phase the color gradually spreads through-
out the emulsion. But if water is the external phase the color does not
spread but is confined to the oil with which it comes in contact on the
surface.
The microscope may be used to determine the type of emulsion formed.
If the oil is dyed red, a red field with clear globules indicates a water-in-
oil emulsion ; red globules in a clear field show an oil-in-water emulsion.
Sometimes a multiple emulsion is obtained, i.e., a dispersed phase within a
dispersed phase. The only means of identifying a multiple emulsion is by
the microscope.
Some food emulsifiers. Seifriz has reported that "olive oil stabilized
with sodium oleate, sodium stearate, gelatose, gum arabic, albumin, lecithin,
saponin, senegin, smilacin, or plant juices (cell sap and protoplasm) forms
oil-in-water emulsions, while the same oil stabilized with casein, gliadin,
cholesterin, or cephalin forms water-in-oil emulsions." Seifriz has also
reported that with casein as the emulsifier the following oils all gave water-
in-oil emulsions: olive, castor bean, poppy seed, sperm, and cod-liver oil.
Linseed oil forms with casein a dual emulsion with the water-in-oil type
predominating. Lecithin favors the formation of oil-in-water emulsions,
whereas cholesterol favors water-in-oil emulsions. Saturated casein solu-
tions with common food fats tend to form water-in-oil emulsions.
In food preparation, various fats and oils are used in the formation of
emulsions. Oils commonly employed are cottonseed, corn, olive, and pea-
nut. The fats include butter, lard, Crisco, Snowdrift, and others. In a
cake batter there are several emulsifiers: the casein of milk, egg yolk, egg
white, and the glutenin, gliadin, and starch of the flour. When equal quan-
tities of fat or oil and emulsifying agents were used, the types of emulsions
formed varied, depending on the emulsifier used and whether the oil was
added to the emulsifier, or vice versa.
With egg yolk all the oils and fats gave a very stable emulsion of the
oil-in-water type. With egg white as the emulsifier, oil forms an oil-in-
water emulsion. Fig. 26 shows an emulsion of corn oil and egg white.
When the oil is added gradually to the egg white, a foam as well as an
emulsion is formed. The large white spheres are air bubbles. The oil is
colored red and in the photomicrograph shows black. The illustration also
shows that the oil is adsorbed in the film or layer at the interface between
a liquid and a gas.
When a given weight of butter is added gradually to an equal weight
of egg white, an oil-in-water emulsion is formed. With the last additions
of the butter the emulsion may break. If beating is continued, a water-
in-oil emulsion may form. In melting butter the curdy part containing
the casein settles to the bottom of the container and consequently is usually
272
EMULSIONS
the last portion to be added to the egg white. It may have some effect
upon the reversal of the emulsion. Sometimes only an oil-in-water emul-
sion forms. Whether this is due to the salt or casein content of the butter
or to the temperature maintained is not known. The emulsion obtained
when egg white is added to the melted butter may be a water-in-oil or
an oil-in-water.
FIG. 26. A coarse emulsion of oil in egg white. Egg white will not foam if a fat
like butter or lard is added to it, but with oil both an emulsion and a foam are
formed when beaten with an egg beater. The large light spheres are air bubbles.
The oil is stained red and appears dark in the photomicrograph. This photomicro-
graph is interesting for it shows the adsorption or concentration of the oil at the
interface between a gas and a liquid (egg white). This adsorption of fat can be
seen in later illustrations of cake batter.
Magnification approximately x 135.
Lard and Crisco form rather unstable emulsions with egg white, but
both types may be formed.
With a saturated casein solution as the emulsifier, the water-in-oil type
of emulsion predominates when butter, lard, Crisco, and oil are used. The
emulsions are rather coarse and unstable.
Efficiency of different substances as emulsifiers. Some emulsify-
ing agents are more efficient than others. No study has been made to
compare the efficiency of the various emulsifiers under different conditions
and for different emulsions. As a class, the hydrophilic colloids seem to be
the most efficient emulsifiers. Clark and Mann have reported the efficiency
of sucrose, dextrin, starch, gum arabic, and egg albumin in emulsions of
benzene and kerosene in water. The oils composed 75 per cent of the total
STABILIZATION BY POWDERS 273
volume in each case. The emulsions were made by shaking in a bottle, the
oil being added in 3 parts and a total of 4800 shakes used in making the
emulsion. They examined the emulsions after standing 1, 4, and 7 weeks
and ranked the emulsifiers for stability on a scale of 10.
With benzene and a 1 per cent solution of each emulsifier the order was
as follows: egg albumin, 10; starch, 6; gum arabic, 5; dextrin, 3; sucrose,
0. With kerosene the order was as follows: egg albumin, 10; starch, 9;
gum arabic, 3 ; dextrin, 2 ; sucrose, 2.
Clark and Mann also determined the efficiency of the above emulsifying
agents in the presence of electrolytes. In some cases the electrolytes in-
creased the viscosity; in others they lowered it. They concluded that "no
one general rule can be made as to the effect which produces the best
emulsions for any one substance nor can any one generalization be made
for the effect which produces the best emulsion for all substances under
all conditions. Those which seem to be of primary importance are viscosity
and film formation."
Brooks reports that egg yolk is four times more efficient in mayonnaise
than egg white.
Types of Emulsifying Agents
Emulsions may be stabilized by different substances. They may be classi-
fied as follows, the basis being upon the type of emulsifier : ( 1 ) those
stabilized by an electric charge, (2) those stabilized by colloids, and (3)
those stabilized by powders.
Stabilization of emulsion by an electric charge. Mineral oil emul-
sions in which the oil is present in very small amounts belong in the group
stabilized by an electric charge. The oil particles are negatively charged.
Hydrophilic sols are stabilized by hydration and an electric charge. Ghosh
and Dhar suggest that emulsions are similar to sols and that the stability,
the separation or coagulation, and the reversal of the emulsion are markedly
influenced by its electric charge.
Emulsions stabilized by colloids. So many of the emulsifiers are
colloidal in nature that this group is the most important in food prepara-
tion. The following are commonly used : eggs, gelatin, flour, starch, and
milk. Gum arabic, gum tragacanth, Irish moss, and other substances are
used less frequently. Pectin is being used to some extent. Gum arabic and
gum tragacanth are used principally in cookery of diabetic foods, the Irish
moss in puddings.
Stabilization by powders. Finely ground particles or powders such
as lampblack, mustard, and paprika are a third class of substances used for
emulsifying agents. The best examples of this type of emulsifier in prepared
foods are the French dressings. At the present time several brands are on
the market that are fairly stable. All are deep red in color, so that the
274 EMULSIONS
emulsion must be partially and probably wholly stabilized with particles of
paprika and mustard. This kind of emulsion is formed by the powder film
around the drops of oil which keeps them from coalescing. Clayton reports
the results of using finely divided solids as emulsifiers by Bechhold, Dede,
and Reiner. "They found that the formation of emulsion depends upon:
(1) the grain size of the powder. The smaller the grain the better the
emulsion, until an optimum is reached, after which smaller grains have
inferior emulsifying properties. (2) The quantity of powder. The more
powder there is available the more globules there can be covered, provid-
ing the powder is sufficiently fine." They report that zinc dust, iron
powder, clay, Kieselguhr, and yeast made very efficient emulsifiers.
The Making of Emulsions
To make an emulsion it is necessary to break or separate the dispersed
phase into small globules. The work for this separation can be done in
different ways. Machines of different types are used for making commercial
emulsions. They are all designed to break the liquid into globules, either
by a rotary motion, pressure, or by some other means. Agitation is used in
all of these. Homogenization is used by most commercial firms for making
mayonnaise. In making emulsions in the home, different methods are fol-
lowed. For mayonnaise, an egg beater is often used, French dressing is often
shaken, and gravy and sauces are made by stirring, usually with a spoon.
Optimum degree of agitation for each emulsion. Clayton says it is
well known that agitation can both break and make an emulsion. The
amount of agitation required for a given emulsion depends upon the par-
ticular emulsion being made and the kind of mixing utensil used. Clayton
states: "It is quite reasonable to believe that for any given emulsifying
apparatus there exists an optimum speed or degree of agitation or mixing,
and an optimum time of mixing or running, whereby the most perfect
emulsion can be obtained in a given system. Experiments prove this."
Stamm has reported that the method of preparation affects the size of
the particles of the dispersed phase. Harkins (1928) states that the "method
used in preparing an emulsion is one of the factors determining the dis-
tribution, but the most striking feature of the present work is that the
shift of the number maximum is so slight with the different methods of
stirring employed." By number maximum Harkins refers to the number
of particles of the dispersed phase in a definite volume. Thus the ap-
paratus, its speed, and the time used in mixing emulsions like mayonnaise,
may or may not determine to a great extent the size of the particles formed
and the stability of the emulsion.
Intermittent mixing for emulsions. Clayton states that what may
be termed the mechanics of emulsification are far from being understood
even now. In some experiments in making different emulsions, investiga-
DOES PEPTIZATION PLAY ROLE IN EMULSIFICATION? 275
tors have reported that intermittent shaking is more effective than con-
tinuous shaking or agitation. Clayton believes that shaking is an inferior
method of making emulsions, but that continuous shaking should give
equally as good results as the intermittent shaking, provided the emulsified
portions are continuously removed from the mass. Intermittent agitation is
explained as being more effective than continuous agitation, because of the
rest periods, which allow time for adsorption of the emulsifying agent.
In making mayonnaise, the beating is often intermittent, for in stopping
to add oil to the mixture, short rest periods occur.
Foams and formation of emulsions. Harkins in commenting on the
method of preparation of emulsions, states that in a number of cases the
emulsion failed to form after stirring rapidly with a motor-driven egg
beater for 5 minutes, which was not in accord with the usual emulsifica-
tion in a few seconds. He found that in all these cases no foam was pro-
duced, and that as soon as a foam formed, emulsification occurred in a few
seconds. This may be a factor in the formation of some emulsions in food
preparation.
MAYONNAISE
Definition by Food and Drug Administration. "Mayonnaise, may-
onnaise dressing, mayonnaise salad dressing, is the semi-solid emulsion of
edible vegetable oil, egg yolk, or whole egg, a vinegar, and/or lemon juice,
with one or more of the following: salt, other seasoning commonly used
in its preparation, sugar and/or dextrose. The finished product contains
not less than 50 per cent of edible vegetable oil."
Does peptization play a role in emulsification? In no theory of
emulsification that the writer has read is peptization mentioned. Yet the
following comments by Bancroft on peptization so vividly describe what
happens in making mayonnaise that they are given. Bancroft, in his chap-
ter, "Preparation of Colloidal Solutions," states that the methods of
making colloidal solutions may be grouped under two heads, the dispersion
and the condensation methods.
The making of mayonnaise, Hollandaise sauce, gravies, and other sauces
in which an emulsion is formed comes under dispersion methods, for
although the dispersed phase is not sufficiently small to class the product
as a sol, the dispersed phase must be broken into many particles. Bancroft
states that one means of dispersion is by the addition of a peptizing agent.
He says that peptization is always due to adsorption. "If an adsorbed film
has a low surface tension on the water side, it will tend to scrunch up and
to peptize the solid as internal phase. If the reverse is the case, the solid
will tend to form the external phase." If the word oil is substituted for
solid in the foregoing quotation, an excellent picture of the formation of
mayonnaise emulsion is obtained. For example, if one-fourth cup of oil is
276 EMULSIONS
added to a cup or more of well-emulsified mayonnaise, the oil may be
stirred slowly a few times with a spoon, 15 to 20, and presto, it is all
emulsified. The stirring could not possibly break the oil into thousands of
small particles. Hence, the function of the stirring is to increase the area
for adsorption to occur and the squeezing effect of the adsorbed egg yolk
breaks the oil into many spheres. For the first addition of oil in making
mayonnaise great care must be taken, but large quantities of oil may be
added rapidly in the last part of the process.
Investigations on Mayonnaise and Emulsions
Air film on the oil phase. Hall and Halstrom have reported that the
presence of an air film on the oil phase, as it is introduced into the emul-
sifier and forming emulsion in making mayonnaise, results in a less stable,
inferior emulsion with lower specific gravity than in mayonnaise prepared
with oil having no such air films. For the emulsions having air films on
the oil, the oil was added from a buret at a definite rate, the point of the
buret being six inches above the surface of the forming emulsion. For oil
having no air film the buret point was lowered so that the oil was injected
beneath the surface of the forming emulsion. They add, "Clayton pre-
dicted that when the dispersed phase is injected into the continuous medium
below the surface, intermittent injection would confer no advantage."
From their results Hall and Halstrom felt that Clayton's prediction was
a sound one.
Water-holding capacity of emulsifier. Kilgore states that preserved
yolks are available in five main conditions : frozen salted, frozen sugared,
fresh refrigerated, especially treated, and dried. This is also the order of
their volume consumption by the mayonnaise trade. Kilgore emphasizes
that the starting mixture to which the oil is added should not contain too
much "free" water. It should have enough "free" moisture to start emulsi-
fication yet have a heavy body, like a thick paste, smooth in texture. Frozen
and treated yolks, because they have more bound and less "free" water than
fresh yolks, are excellent for starting mayonnaise to secure a fine "grain."
Yet more of the frozen than of fresh yolks are necessary for an emulsion of
good consistency. Kilgore adds that de-fatted mustard flour is an excellent
water-holding ingredient ; hence it gives a heavy paste and also has decided
emulsifying powers.
Emulsifying properties of mustard. Kilgore determined the emulsi-
fying properties of mustard in three ways: (1) Foaming ability, (2) the
stability of oil drops on a mustard solution, and (3) the stability of emul-
sions made with mustard solution as the sole emulsifying agent. In a 75-
pound batch of mayonnaise about 8 to 9 pounds of vinegar and 5 to 6
ounces of mustard are used, which gives about 3.5 per cent concentration
of mustard. The concentrations of mustards used were: 0.1, 0.5, 1.0, 2.0,
and 4.0 per cent.
THE METHOD OF MIXING 277
Foaming. The mustard was weighed and added to water in glass-
stoppered bottles and shaken. Little foam was formed except with the 2
and 4 per cent concentrations. Good emulsifiers for oil-in-water emulsions
usually foam readily in water.
Oil drops on mustard solution. The mustard solutions were obtained by
adding the mustard to water and filtering off the residues of undissolved
mustard. About 70 per cent of the mustard was found to be soluble. If
drops of oil such as corn oil are poured on water, they spread in a film
over the surface of the water. But when drops of oil are placed on water
containing an emulsifying agent which favors the formation of an oil-in-
water emulsion, spreading does not occur. The drops remain separate and
distinct. Kilgore found that a 1 per cent mustard solution afforded protec-
tion for the oil drops but a 4 per cent solution gave much greater protection.
Stability of mustard emulsions. The corn oil was added slowly to the
mustard solution as in making mayonnaise, a high-speed drink mixer being
used as a whip. After being stored for one year the emulsions made with
0.1, 0.5, and 1.0 per cent of mustard were broken. Those with 2.0 per cent
had some oil on top; and the emulsion with 4.0 per cent mustard did not
break and showed no leakage of oil, although it contained 80 per cent
of oil.
Corran formed a water-in-oil emulsion of olive oil and lime water. To
this emulsion mustard was added. When the concentration of mustard
reached 2 per cent, the emulsion broke and reformed as an oil-in-water
emulsion. Fine mustard flour was more efficient than coarse mustard flour.
Kilgore in continuing his work with mustard and emulsification found
that mayonnaise without mustard had a stiffer consistency than that with
a de-fatted mustard flour. But he found this depended on how the mustard
was added. If added dry it decreased initial stiffness, but if added wet it
increased the stiffness. De-fatted yellow mustard flour lost its emulsifying
properties if mixed with vinegar and allowed to stand longer than a day;
whereas this was not the case with mustard having a high oil content.
Emulsifying properties of oils. Meszaros states the size of the fat
drops in an emulsion depends more on the method of preparation than on
the properties of the fat. Meszaros has expressed the emulsification capacity
in a number (E number) which represents the milligrams of fat which
can be emulsified under certain conditions in 100 grams of water without
the aid of emulsifying agents. Fats tested fall in four groups : ( 1 ) Fats
which show a very good emulsification capacity (E number over 50) ; as
goose fat, horse fat, lard, crude rapeseed oil (crude sunflower oil). (2) Good
emulsifying fats (E number 20-50), as butter, butter fat, peanut oil,
sesame oil. (3) Poor emulsifying fats (E number about 10) coconut oil,
palm-kernel oil, soybean oil, beef tallow. (4) Very poor emulsifying fats
(E number 10) illipe fat, hardened train oil.
The method of mixing. Kilgore, Corran, and Hall and Halstrom
278
EMULSIONS
emphasize the method of adding the oil to secure a stable emulsion of
desirable consistency. Hall and Halstrom found that the method they
called the Compromise Method was the best. For this method a portion of
the oil was added by means of a buret above or beneath the surface of the
forming emulsion until optimum dispersion was obtained. They state that
optimum dispersion might properly be considered the critical dispersion
point. At this point maximum thickness is attained and any further addi-
tion of oil results in an irrecoverable breaking of the emulsion. This oc-
curred after the addition of 30 to 35 cc. of oil to 20 grams of beaten egg
yolk. At this point the vinegar and spices are added. This thins the
emulsion but thickening occurs again with the addition of the remainder
of the oil. The amount of oil added was such that the mayonnaise con-
tained 89 to 93 per cent of oil.
For the method which Hall and Halstrom called American, the vinegar
and spices were added to the egg yolk. After blending of these ingredients
the oil was added in the same manner as for the compromise method.
Their results follow :
TABLE 40
STABILITY OF MAYONNAISE (Hall and Halstrom)
Method
Manner in which
oil was added
Stability of emulsion after
storing at 8C. for 2 years
Compromise
Above surface
Fragile, partially separated
Compromise
American .
Beneath surface
Above surface
No separation
Complete separation
American
Beneath surface
No visible separation, but fragile
The emulsifying constituent of egg yolk. In starting their investi-
gation, Snell, Olsen, and Kremers added lecithin to egg yolk in making
mayonnaise. They acted under the general assumption that lecithin is the
constituent of egg yolk which is effective in producing emulsions. Hence
it was thought that the addition of more lecithin should increase the
stability of the mayonnaise. But all the mayonnaises so produced had poor
consistency. Next they studied the effect of each of the known major con-
stituents of egg yolk on mayonnaise. It was found that none of these sub-
stances was capable of producing the consistency derived from the whole
egg yolk.
This led to the investigation which demonstrated that egg yolk owes
its emulsifying action to an .unstable complex containing both lecithin and
protein, which they called "lecitho-protein." This lecitho-protein consti-
tuted about 32.5 per cent of the salted yolks.
THE METHOD OF MIXING 279
Factors Affecting the Ease of Formation and
Stability of Mayonnaise
In making mayonnaise, several factors affect the formation of the emul-
sion, its stability, and ease of making. The major factors may be listed as
follows: (1) degree and kind of agitation, (2) the method of mixing,
(3) the ingredients used, and (4) temperature. Some of these may be
further subdivided.
Degree and kind of agitation. This factor has already been partially
discussed. Under it can be included the kind of apparatus used as well as
rate of agitation. Good stable mayonnaises may be formed by both con-
tinuous and intermittent agitation. Hall and Halstrom have demonstrated
that very stable concentrated mayonnaise may be formed by continuous
agitation if the oil is added beneath the surface of the forming emulsion.
Clayton states that it is a well-known fact that agitation can both make
and break an emulsion. It has often been observed in the laboratory, when
the vinegar and seasoning have been added to the egg yolk before any oil
is added, that rapid agitation for the first additions of oil is advantageous;
otherwise the resulting mayonnaise is less viscous.
The kind of bowl used. Some failures in making mayonnaise are due
to putting small quantities of the egg yolk in a large mixing bowl. As a
result the egg yolk spreads out in such a thin layer that the egg beater
picks up very little of the egg and an emulsion is not formed with the first
portions of the oil added. Sometimes the rod at the bottom of the rotary
egg beater is thick and holds the beater above the contents of the bowl,
provided the quantity of material in the bowl is small and the egg beater
is held upright.
The method of mixing. Under the method of mixing may be grouped
the following: (1) the method of adding the oil, (2) the quantity of oil
that is added at first, (3) the time of adding the vinegar, and (4) the time
the seasonings are added.
The method of adding the oil. Hall and Halstrom have shown that a
more stable emulsion is formed when the oil is added beneath the surface
of the forming emulsion.
The quantity of oil that is added at first. Often the statement is seen
that mayonnaise can be made by putting all the ingredients in the mixing
bowl and then beating. The author (see Experiment 52C,3) has never
been able to do this and has never witnessed the making of it in this way.
Many water-and-oil emulsions can be made by putting all the ingredients
together and shaking or stirring, but mayonnaise does not seem to belong
to this group. It is possible that some factors may occasionally influence
the formation of an emulsion so that it is formed when all the ingredients
are added at once to make mayonnaise.
Mark expresses the amount of oil that can be added and an emulsion
280 EMULSIONS
obtained as follows: "(I) If the proportion of oil to that of egg or of the
emulsion already produced was kept below a certain maximum a stable
emulsion always resulted, no matter what the temperature or manner of
beating, (2) that if the proportion of oil added exceeded a certain maxi-
mum, the egg or the emulsion already formed became dispersed in oil and
no permanent emulsion was formed, (3) that if the proportion between
these limits were used a permanent emulsion might or might not be formed,
dependent on such variables as manner of beating and temperature, (4) that
if egg was previously diluted by adding vinegar the proportion of oil
which could be permanently emulsified was greatly increased during the
addition of the first and second portions of oil, but that as viscosity of the
mixture increased the maximum ratio of oil to emulsion rapidly approached
the value found when egg alone was used at first."
Mayonnaise is formed more readily if the quantity of oil added at first
is small. But the quantity of oil that can be added to egg yolk for the first
addition of oil and still obtain a stable emulsion depends somewhat upon
the rate of agitation, the combined volume of egg yolk and vinegar, the
temperature of the ingredients, and other factors. If the above factors are
standardized and if the combined volume of the vinegar and the egg yolk
is l /4 cup, the quantity of oil that can be added and emulsified is a definite
quantity. If the combined egg yolk and vinegar is j/2 cup, the quantity of
oil that can be added will be 2 times as much as for l /4 cup under the same
conditions. Using 1 egg yolk and 15 cc. of vinegar and beating with a
rotary egg beater in a round-bottomed jar, Experiment 52C, 2, 12 tea-
spoons of oil have been the limit for the first addition of oil. Often only
10 or 11 teaspoons can be added. This large quantity of oil must be care-
fully emulsified before the second portion of oil is added. The volume of
the egg yolk and vinegar is a little over 2 tablespoons. Thus the volume
of oil that can be added, 7 to 10 teaspoons, is about the same as the
volume of the egg yolk plus the vinegar. The emulsion is formed more
easily if smaller quantities, 2 to 3 teaspoons, of oil are added at first. The
second addition of oil, and any subsequent addition, must not exceed a
definite relation to the volume of emulsion already formed. In making
salad dressing with 1 egg, 1 cup of cornstarch paste, a cup of oil, and
vinegar, all the oil can be added at first, but here again the volume of the
oil is about the same as that of the emulsifier, i.e., the egg yolk plus the
cornstarch paste.
The time of adding the vinegar. Part or all of the vinegar may be
added at various intervals during the mixing or it may be added to the egg
yolk alternately with the oil. It may be added after considerable oil is
added to the egg yolk (Experiment 52A,1,2,3) or before any oil is added.
By the last method the oil may be added in larger quantities for the first
and second additions, and the mayonnaise made more rapidly. However,
the size of the oil particles that are first emulsified is quite large when the
vinegar is added to the egg yolk before the oil is added. But with each
THE INGREDIENTS USED 281
subsequent addition of oil the dispersed particles become smaller, and the
mayonnaise stiffen This is shown in Figs. 27 to 30, which are photo-
micrographs of mayonnaise. If the oil is added to the egg yolk before the
vinegar, the first oil particles emulsified are very small and remain small
with subsequent additions of oil. When the vinegar is added, the dispersed
globules become larger, and the mayonnaise less stiff.
Kilgore suggests the following method. The salt, mustard, and other dry
seasonings are added at first to fresh egg yolks, for they aid in holding the
excess moisture. To this is added just enough vinegar to make a heavy
paste. Then run in the oil until half is added, add another portion of
vinegar, equal to that at the start, and the remainder at the end of the
batch.
Corran suggests that the emulsification be carried out in three stages.
( 1 ) The dry ingredients, egg yolk, and part of the aqueous ingredients
are mixed thoroughly. (2) All the oil is added, forming a creamy nucleus.
(3) The creamy nucleus is diluted with the remainder of the aqueous
ingredients.
The ingredients used. These include the oil, the salt and seasonings,
the vinegar, the egg yolks, and even previously emulsified mayonnaise.
Any of the edible oils may be used in mayonnaise.
Salt and seasonings. Salt, mustard, paprika, and pepper are usually
added to mayonnaise. Small amounts of other seasonings may be used.
Pasteurized spice mixtures are also now available to the mayonnaise manu-
facturer. The addition of an electrolyte to an emulsion may produce
different results, depending upon the electrolyte, the emulsifier, and the
type of emulsion. Some electrolytes cause reversal of certain emulsions;
others may tend to stabilize the emulsion. Seifriz in his work with emul-
sions stabilized with casein found that sodium chloride had no influence
on the water-in-oil emulsions, but tended to stabilize oil-in-water emul-
sions. The effect of sodium chloride would probably vary with the emul-
sifier and the concentration of the salt. Krantz and Gordon found that
the concentration of the sodium chloride affected the stability of some
emulsions. In mayonnaise, when egg yolk is used as the emulsifier and
with the proportion of salt given in Experiment 52, it has been found that
the addition of the salt to the egg yolk before the addition of any oil tends
to stabilize the emulsion. In these experiments the vinegar was also added
to the egg yolk before the oil was added. When the salt is added to the
mayonnaise after the oil has been added, the size of the dispersed oil
globules is larger and the emulsion breaks more readily while it is being
made, indicating a lessened stability. The amount of salt used in the recipe
may tend to lessen the solubility of the egg proteins sufficiently so that a
more tenacious film is formed. If the concentration of the salt is great
enough to "salt out" the egg proteins, then different results would be
obtained. Thus it seems preferable to add the salt to the egg yolk and
vinegar before adding the oil in making mayonnaise. Calcium salts, since
282
EMULSIONS
FIG. 27. Mayonnaise. Showing the coarse emulsion formed after the addition of
one tablespoon of oil. The vinegar and seasonings were added to the egg yolk,
before the oil was added. Magnification approximately x 200.
FIG. 28. Mayonnaise. Same as Fig. 27, but after adding one-fourth cup of oil.
Magnification approximately x 200.
THE INGREDIENTS USED
283
FIG. 29. Mayonnaise. Same as Fig. 28, but after adding three-eighths cup of
oil. As the oil spheres become smaller with the addition of more oil the mayon-
naise becomes stiffer. Magnification approximately x 200.
FIG. 30. Mayonnaise. Same as Fig. 29, but after the addition of one-half cup
of oil. Magnification approximately x 200.
284 EMULSIONS
they tend to form water-in-ofl emulsions, are detrimental to mayonnaise.
Hence it is recommended that the salt used should contain less than 0.1 per
cent of foreign calcium salts. Kilgore's results indicate it is preferable to
add the mustard to at least part of the vinegar to make a paste. This is
then added to the egg yolk.
Egg yolks. Johnson and Mark have reported that cold-storage eggs are
inferior to fresh eggs for making mayonnaise.
However, frozen yolks, either salted or sugared, are more extensively
used at the present time than fresh yolks. Kilgore states the fresh yolk is
usually too light in body to produce a good emulsion at the start. This is
true in spite of the fact that fresh yolk is the best possible emulsifier and
that less can be used than is required for frozen yolk. The freezing
changes the physical consistency of the yolk. Upon defrosting the frozen
yolks are very thick and paste like, owing to the binding of the water
during freezing.
The addition of a small amount of e7Jiulsified mayonnaise. Mayonnaise
is very easily made if from y\ to 1/3 cup of previously made mayonnaise is
added to the egg yolk and vinegar. This gives a larger quantity of mate-
rial to work with, but if an emulsion is already started the emulsification
of additional oil is accomplished more readily. After an emulsion is once
formed, subsequent additions of oil are very easily emulsified. This is
analogous to seeding in crystal formation and the addition of an old gel
to gelatin to hasten jelly formation. Egg yolk is itself an emulsion con-
taining about 30 per cent of fat.
Kilgore states, "another solution to the problem of producing high con-
sistency mayonnaise having medium or low yolk content, is to start the
emulsion by means of some finished mayonnaise added to the yolk and
spices. This trick of starting an emulsion, or 'seeding' it, by means of one
previously made is common in pharmaceuticals. It is the fundamental prin-
ciple of a process for continuous emulsification."
Temperature. Clayton states that, in general, the effect of rise in tem-
perature is to make emulsification easier. The reason for this is that
viscosity is reduced with a rise in temperature, but more important, a rise
in temperature is accompanied by a decrease in the interfacial tension of
non-miscible liquids. Branch states that in commercial production of may-
onnaise the temperature of the mixing room is kept at 65 to 75 F.
Breaking Mayonnaise
Water may separate at the bottom of a mayonnaise after long standing.
Robinson states that this seldom occurs if the amount of water in the mayon-
naise does not exceed 15 per cent. With the percentage of water higher
than 15 the separation occurs more frequently.
Oil may separate at the top of the mayonnaise. Anything that destroys
the film-forming properties of the emulsifying agent and lets the dispersed
CONCENTRATION OF OIL IN MAYONNAISE 285
phase run together destroys the emulsion. Over-heating, when the oil and
liquid expand at different rates, the additions of salts, drying of the sur-
face, freezing, and jarring may all cause separation in mayonnaise. The
addition of enough salt (sodium chloride) to "salt out" the emulsifier
will break emulsions stabilized with proteins, but this requires far more
salt than is ordinarily used in mayonnaise. The amount commonly used
aids in stabilizing the mayonnaise.
Freezing dehydrates the egg, because the water separates from the egg
protein in ice crystals, thus breaking the film. Agitation or shaking in
shipping tends to break the emulsion. Evaporation from the surface of the
mayonnaise may cause drying of the emulsifying agent and consequently
coalescing of the oil on the surface. Mayonnaise keeps better in covered
containers which prevent evaporation. Fischer and Hooker state that, if
the protein emulsifier is diluted beyond the point at which it will take up
all the water, the emulsion tends to break. Heating, resulting in too much
evaporation of the liquid, causes separation of the fat in gravies, sauces, and
cream puffs.
Re-forming broken mayonnaise. The usual procedure to re-form
broken mayonnaise is to take a new egg yolk and add the curdled, broken
mayonnaise to this gradually. It is added and beaten in the same manner
as when the oil is originally added to the egg yolk. But it is not necessary
to use egg yolk to re-form the emulsion. It can be re-formed by adding
the broken emulsion gradually to a tablespoon of water or vinegar. The
broken emulsion must be added gradually to the water or vinegar and
beaten during the addition. It will not re-form if the water or vinegar is
added to the mass of broken emulsion. See Experiment 52, D.
The Concentration of Oil in Mayonnaise
The amount of oil that can be permanently emulsified varies with the
emulsifier, the oil used, and the manner in which it is added. Pickering
has emulsified "99 per cent of paraffin oil in 1 cc. of 1 per cent potash solu-
tion by successive addition of small portions." The concentration of oil in
food emulsions varies from a very low percentage up to about 85 per cent.
Mayonnaise containing slightly more than 95 per cent of oil has been
made in the laboratory, but it usually breaks shortly after a little more
than 90 per cent of oil has been added. The stiffening of mayonnaise
containing over 90 per cent of oil makes it difficult to mix the last addition
of oil. Mayonnaise with more than 90 per cent of oil resembles jelly in
consistency; cut with a knife or spoon it retains its shape. It will keep
varying lengths of time in a covered jar in the refrigerator. Some break in
a short time, but most of them keep for several days or weeks. Probably
this variation in breaking is partially due to variations in beating in form-
ing emulsions. After standing a short time, if the dressing is cut or if some
is lifted out of the jar, there is a tendency for oil drops to form gradually
286 EMULSIONS
on the cut surface. It separates more readily than mayonnaise with a
lower percentage of oil. Ordinary mayonnaise containing from y 2 to y\
cup of oil to- 1 egg yolk, and 15 cc. of vinegar averages from 65 to 75
per cent of oil. Hall and Halstrom, by introducing the oil beneath the
surface of the forming emulsion, obtained mayonnaise with a concentration
of 89 to 93 per cent of oil that remained stable for two years when stored
at 8C.
Some Food Emulsions
Salad dressing. The Food and Drug Administration has defined
mayonnaise as being made with either egg yolk or whole egg. Hence, a
product which may be similar to mayonnaise but stabilized with egg white,
or part egg yolk and part starch paste, is called a salad dressing. Home-
makers have used many emulsifying agents such as egg yolk, whole egg,
egg white, cooked egg yolk, gelatin, starch paste, meat extract, and mashed
potato. However, they are not equally efficient. The order for efficiency
is as follows : egg yolk, whole egg, egg white, gelatin, and starch paste.
Fats such as butter and lard may be melted and substituted in a mayon-
naise formula, but the product is a salad dressing. Mineral oil may also be
used in a mayonnaise- formula. Boiled salad dressings are also emulsions.
French dressings. French dressings are usually temporary emulsions,
but some are quite stable. There, seems to be less separation of oil at the
top and of water at the bottom, if the phase-volume rule is observed, and
the oil composes about 74 per cent of the emulsion. .The seasonings, pow-
dered paprika and mustard, are the emulsifiers. It is possible that traces
of some substances in the vinegar may occasionally aid emulsification.
Emulsions stabilized with flour. In gravies and sauces the amount of
oil that can be permanently emulsified is much smaller than in mayonnaise.
Gravies and sauces in which the oil separates may be made smooth again
by adding water and stirring while heating. The addition of water lessens
the percentage of oil in the product. Emulsions stabilized with flour or
starch need a higher percentage of water than mayonnaise. The starch
absorbs a large portion of the liquid, which accounts for a large part of
the water, but even if the maximum absorptive power of the starch is
accounted for a large amount of water is still needed. This type of emul-
sion belongs in the class of hydrated colloids referred to by Fischer and
Hooker, in which they state that the water must not be reduced below
a lo\ver limit and must not exceed an upper limit.
Cream puffs. Cream puffs are good examples of a batter in which the
fat is emulsified. See Chapter XII, Experiment 80. In the recipe as given
in the experiment, the fat constitutes about 17 per cent of the uncooked
ingredients, if the fat content of the butter is used as 85, the eggs as 10.5,
and the flour as 1.5 per cent. The cooking of the water, flour, and fat will
increase this percentage, as will the baking, on account of evaporation of
REFERENCES 287
water. The fat does not run or ooze out of the dough while the puffs are
baking.
If the eggs in the recipe are reduced to 2 but no other change is made,
Experiment 80C,2, the percentage of fat in uncooked materials is about
18.6. The fat in these puffs runs out of the dough and over the baking pan
in large quantities while baking. With the smaller quantity of egg the emul-
sion does not hold, but if the amount of water added is increased to 1*4
cups when the eggs are reduced to 2, the amount of fat in the uncooked
ingredients is about 17 per cent. The fat in these puffs does not ooze
out while they are baking. Although the quantity of egg is important, this
also shows that it is essential to have a definite proportion of liquid to
prevent breaking of the emulsion.
Cakes. The fat in a cake batter may or may not be emulsified. A micro-
scopic study of cake batters shows that there is a tendency for oils to be
emulsified as oil-in-water emulsions, no matter what the method of mixing.
Often the oil is not wholly emulsified, the degree of emulsification varying
with the extent of mixing, the temperature, and other factors. When butter
or hard fats are used in cakes or batter products, they may be partially or
wholly emulsified, if they are melted before adding to the batter and pro-
vided the temperature of the batter is not so low as to chill the fat quickly ;
or they may be emulsified if the temperature of the ingredients is above the
melting point of the fat, so that the fat is melted. In ordinary methods
and temperatures of mixing cakes, the butter and hard fats do not give
oil-in-water emulsions.
LITERATURE CITED AND REFERENCES
Bancroft, W. D. Theory of Emulsification. I, II, III, IV, V, J. Physical Chem.
16: 179, 345, 474, 739 (1912) ; 17: 501 (1913).
Bancroft, W. D. Applied Colloid Chemistry. Chapters VII and IX. McGraw-
Hill Co. Third Ed. (1932).
Bhatnagar, S. S. Studies in Emulsions. III. Further Investigations on the
Reversal of Type by Electrolytes. J. Chem. Soc. 119: 1760 (1921).
Branch, E. L. Production of Commercial Mayonnaise. Am. Food J. 19: 460
(1924).
Brooks, R. O. The Science of Mayonnaise Manufacture. The Canner. June
4. p. 37 (1927).
Clark, G. L., and Mann, W. A. A Quantitative Study of the Adsorption in
Solution and at Interfaces of Sugars, Dextrin, Starch, Gum Arabic, and Egg
Albumin, and the Mechanism of Their Action as Emulsifying Agents. J.
Biol. Chem. 52: 157 (1922).
Clayton, W. The Theory of Emulsions and Their Technical Treatment. J. & A.
Churchill. Third edition (1935).
Clowes, G. H. A. Protoplasmic Equilibrium. I. Action of Antagonistic Elec-
trolytes on Emulsions and Living Cells. J. Physical Chem. 20: 407 (1916).
Corran, J. W. Emulsification by Mustard. Food Manufacture. 9: 17 (1934).
Finkle, F., Draper, H. D., and Hildebrand, J. H. The Theory of Emulsification.
National Symposium on Colloid Chemistry. Vol. I. p. 196 (1923).
Fischer, M. H. Soaps and Proteins. John Wiley & Sons (1921).
288 EMULSIONS
Fischer, M. H., and Hooker, M. D. Fat and Fatty Degeneration. John Wiley
& Sons (1917).
Fischer, M. H. Emulsification. Oil & Soap 13: 30 (1936).
Gray, D. M., and Southwick, C. A., Jr. The Mayonnaise Emulsion. The Glass
Packer 2: 17, 77 (1929).
Ghosh, S., and Dhar, N. R. The Influence of Ions Carrying the Same Charge
as the Dispersed Particles in Inversion of Emulsion. J. Physical Chem. 30:
294 (1926).
Hall, I. S., and Halstrom, E. E. The Effect of an Air Film on the Oil Phase
of Emulsions of the Mayonnaise Variety and a Comparison of Two Methods
of Preparation. A paper given at Am. Home Econ. Assoc., Seattle, July 7
(1936). Also personal communication.
Harkins, W. D. The Stability of Emulsions, Monomolecular and Polymolecular
Films, Thickness of the Water Film in Salt Solution and the Spreading of
Liquids. Colloid Symposium Monograph. Vol. V. Chemical Catalog Co.
(1928).
Harkins, W. D., and Kieth, E. B. The Oriented Wedge Theory of Emulsions.
Sci. 59: 463 (1924).
Hildebrand, J. H. The Theory of Emulsification, Chapter VII, The Theory and
Application of Colloidal Behavior. Edited by R. H. Bogue. McGraw-Hill
Co. (1924).
Holmes, H. N. Emulsions and Foams. Chapter VIII. The Theory and Applica-
tion of Colloidal Behavior. Edited by R. H. Bogue. McGraw-Hill Co. (1924).
Johnstone, M. Mayonnaise Dressing. J. Home Econ. 6: 476 (1914).
Kilgore, L. B. Observations on the Proper Amount of Yolk in Mayonnaise.
U. S. Egg and Poultry Mag. 39: 42, March (1933).
Kilgore, L. B. Egg Yolk "Makes" Mayonnaise. Food Ind. 7: 299 (1935).
Kilgore, L. B. The Mustard and the Mayonnaise. Glass Packer 11: 621 (1932)
and 12: 97 (1933).
Krantz, J. C. Jr., and Gordon, N. E. Emulsions and the Effect of Hydrogen
Ion Concentration upon Their Stability. Colloid Symposium Monograph.
Vol. VI. p. 173 (1928).
Langmuir, I. The Constitution and Fundamental Properties of Solids and Liquids.
II. Liquids. J. Am. Chem. Soc. 39: 1848 (1917).
Mark, K. L. Emulsification in Mayonnaise. J. Home Econ. 13: 447 (1921).
Mayonnaise, an article. Preparation and formula for processing mayonnaise.
Canning Age 16: 328 (1935).
Meszaros, G. The Emulsification Capacity of Edible Fats. Z. Untersuch Lebensum
69: 318 (1936) ; Abstracted in Oil & Soap 13: 20 (1936).
Pickering, S. W. Emulsions. J. Chem. Soc. 91: 2001 (1907).
Robinson, S. K. Practise in Mayonnaise Manufacture. Am. Food J. 19: 185
(1924).
Rogers, L. A. Fundamentals of Dairy Science. By Associates of Rogers. Chem-
ical Catalog Co. (1935).
Seifriz, W. Studies in Emulsions. I. Types of Hydrocarbon Oil Emulsions. II.
The Effect of Electrolytes on Petroleum Oil Emulsions. J. Physical Chem.
29: 587 (1925). III. Double Reversal of Oil Emulsions Occasioned by the
Same Electrolyte. IV. Multiple Systems. V. The Stabilization Membrane.
J. Physical Chem. 29: 738 (1925).' VI. The Effect of Acidity on Type and
Reversibility of Emulsions. VII. The Effect of Phase Ratio and of Method
in Handling on Emulsion Type. VIII. A Comparison of the Behavior of
Vegetable Oils with that of Petroleum Oils. J. Physical Chem. 29: 834 (1925).
Snell, H. M., Olsen, A. G., and Kremers, R. E. Lecitho-Protein. The Emulsifying
Ingredient in Egg Yolk. Ind. Eng. Chem. 27: 1222 (1935).
Stamm, A. J. Experimental Study of Emulsification on the Basis of Distribution
EMULSIONS
289
of Size of Particles. Colloidal Symposium Monograph.
Chemical Catalog Co. (1925).
Thomas, A. W. Emulsions, A Review of the Literature.
12: 177 (1920).
Vol. III. p. 251.
Ind. Eng. Chem.
Mustard ^4 teaspoon
Paprika Y^ teaspoon
Sugar ]/2 teaspoon
EMULSIONS
Experiment 52.
To determine some of the factors that affect the formation and stability of
emulsions.
Mayonnaise:
Egg yolk 1 18 grams
Vinegar 1 tablespoon 15 grams
Oil y?. cup 108 grams
Salt >2 teaspoon
In studying emulsions, a microscope is a great aid. For very fine emulsions
a small portion is placed on a slide and covered with a cover glass. With coarse
and unstable emulsions it is better not to use a cover glass for the weight of
the cover glass often breaks the emulsion. If the oil or fat is colored a dark
red with Scarlet R, the type of emulsion formed can be determined with the
microscope. An oil-in-water emulsion has a red oil dispersed in small spheres;
a water-in-oil emulsion has a red field and light-colored spheres. To color the
oil or fat, add the powdered Scarlet R and then stir. It should stand over
night to dissolve the dye thoroughly.
Store the emulsions in jelly glasses. Label, then cover the glasses to prevent
evaporation. Put away in the refrigerator to determine the permanency of
the emulsion.
A. To determine the effect of varying the method of combining the in-
gredients in making mayonnaise.
1. Put the egg yolk into a small bowl, add the seasonings and the vinegar,
and beat with a rotary egg beater. It may be necessary to tilt the bowl or egg
beater at first, in order that the egg beater blades may come in contact with
the small amount of material. Add the oil in small quantities at first, about ^2
teaspoon, then in larger quantities as the emulsion is formed.
2. Mix the egg yolk and seasoning. Follow directions under Al, for beating.
Add about r /2 teaspoon of oil. Beat, then add ^2 teaspoon of vinegar. Beat.
Continue adding oil and vinegar alternately. After all the vinegar is added,
add the oil in larger quantities.
3. Beat the egg yolk. Follow directions under Al, for beating. Add the
oil a few drops at a time. After the emulsion is forming add the oil in
larger quantities. Add the vinegar slowly after the oil is added. Add the
seasoning last.
Texture
Stiffness
Ease of making
Flavor
Comments
Results and conclusions.
290 EMULSIONS
B. To determine the effect of the temperature of the ingredients in making
mayonnaise.
1. Add the vinegar and seasoning to the egg yolk. Beat. Chill in the re-
frigerator, then set mixing bowl in ice, and add chilled oil slowly. Follow
directions under Al, for adding the oil.
2. Heat the oil and vinegar to 100C. Combine as in Al.
C. To see how much oil can be added for the first addition to 1 egg yolk
and 15 cc. of vinegar and obtain an emulsion.
1. Repeat Al, but add 6 or 7 teaspoons of oil at first, then beat and emulsify
before more oil is added. Add the same amount of oil for the second portion;
then increase the amount for the following additions of oil.
2. If 7 teaspoons of oil can be added under Cl, repeat with 8 teaspoons.
Repeat Cl, adding 9 or 10 teaspoons of oil. Increase the quantity of oil for
the first addition as long as an emulsion is obtained.
3. Put all the ingredients in the mixing bowl together. Then beat with a
rotary egg beater. After beating a few seconds, let the mixture stand; then
beat again. Is an emulsion obtained?
D. To determine the amount of oil that can be added to mayonnaise with-
out breaking the emulsion.
1. Follow directions under Al, but add all the oil possible to the mayon-
naise. Keep a record of the amount of oil added. Compare the consistency of
the mayonnaise with that obtained in other experiments. Determine its keeping
qualities.
2. Repeat Dl, but add oil until the emulsion breaks. If oil has been added
until the emulsion breaks under Dl, use it for this experiment and repeat
D2, but do not add quite so much oil. Put a small portion of the broken
emulsion, about a tablespoon, in a jelly glass. Label and cover. Divide the
remaining broken mass into three parts.
a. Add part one to an egg yolk gradually, beating with the egg beater
during the process. What happens?
b. Repeat D2,a, but add the second portion of curdled emulsion gradually
to a tablespoon of water or vinegar.
c. Add a tablespoon of water or vinegar to the third portion of broken
emulsion. Beat. What happens?
E. To determine the kinds of fat that may be used in mayonnaise.
1. Repeat Al, but substitute butter for the oil. Melt the butter over hot
water and keep warm while adding to the egg yolk and seasonings.
2. Repeat El, but use lard, Crisco, or Snowdrift.
F. To determine the effect of substituting other emulsifying agents for the
egg yolk in making salad dressing.
1. Substitute \y 2 tablespoons of cornstarch paste for the egg yolk in the
mayonnaise recipe. (Make the paste by cooking \ l / 2 tablespoons of cornstarch
with 1 cup of water.) When the paste is cool but not firm, add the season-
ings and vinegar to \ l / 2 tablespoons of the paste and beat with rotary egg
beater. Add the oil slowly at first, then more rapidly after the emulsion begins
to form.
2. Substitute lJ/2 tablespoons of gelatin for the egg yolk in the mayonnaise
recipe. (Make gelatin solution by using 3 teaspoons of gelatin to 1 cup of
water.) When the gelatin is thick but not firm put \ l / 2 tablespoons in a mixing
EMULSIONS 291
bowl. Add the seasonings, and the vinegar. Beat. Add the oil slowly at first,
then more rapidly.
3. Substitute 18 grams of egg white for the egg yolk.
4. Substitute 18 grams of whole egg for the egg yolk.
Is there much difference in the method of combining ingredients for mayon-
naise when egg yolk is used as the emulsifying agent? What effect does the
temperature of the ingredients have on the formation of an emulsion? Did you
succeed in obtaining an emulsion when the oil and all the other ingredients
were combined in a bowl before beating? What is the largest quantity of oil
used for the first addition of oil and a permanent emulsion obtained? How
much oil did you succeed in adding to the mayonnaise? By examining the
emulsions obtained under the microscope, compare cornstarch paste, gelatin,
egg white, and egg yolk as emulsifying agents for emulsions.
Experiment 53.
To determine the type of emulsion formed with different emulsifying agents
and oils or fats.
Use oil or fat stained with Scarlet R. Continue beating the mixture for a
few seconds after all the fat or oil is added, even if at first it appears that
an emulsion will not form. Examine portions of different steps under the
microscope.
1. Use a deep, narrow bowl and a rotary egg beater. Add 25 grams of
melted butter gradually to 25 grams of egg white.
2. Add 25 grams of melted butter gradually to 25 grams of casein solution.
Make the casein solution by adding some powdered casein to water and stir
to dissolve as much as possible. After it settles use the clear liquid. The experi-
ment may be repeated using milk.
3. Repeat 52,1, but use oil instead of butter.
4. Repeat 52,1, but use lard, Crisco, or Snowdrift instead of butter.
5. Repeat 52,2, but use oil instead of butter.
6. Repeat 52,2, but use lard or Crisco instead of butter.
Experiment 54.
A. To determine the proportion of oil and liquid that separates most slowly
in French dressing.
Mustard ^ teaspoon about 0.8 gram
Paprika ]4. teaspoon 1 gram
Salt >^ teaspoon 2 grams
Powdered sugar 1 teaspoon
Add the seasoning to the vinegar and mix. Use a rotary egg beater or a
mayonnaise mixer. A 100-cc. graduate is excellent to weigh the oil in. The
duplicate portions with lemon juice can be measured by filling to the same
height in the graduate. The oil is easily poured from the graduate. Add the
oil gradually to the vinegar and seasonings. A duplicate series may be made
and the ingredients shaken in a flask.
1. Use 15 grams of vinegar and 82 grams of oil.
2. Use 20 grams of vinegar and 77 grams of oil.
3. Use 25 grams of vinegar and 72 grams of oil.
292 EMULSIONS
4. Use 30 grams of vinegar and 67 grams of oil.
B. To determine the effect of substituting lemon juice for the vinegar.
Repeat 54A, substituting lemon juice for the vinegar.
C. To determine the effect of increasing the quantity of paprika.
Use the proportion of oil and vinegar found best under A. Different brands
of paprika may be used as they may vary in fineness. The seasonings may
all be put in a mortar and ground before using.
1. Use 1 teaspoon (2 grams) of paprik?..
2. Use \ l /2 teaspoons (3 grams) of paprika.
3. Use 1 teaspoon (2 grams) of paprika and 1 teaspoon (about 1 gram)
of mustard.
CHAPTER IX
MILK AND CHEESE
In food preparation, milk is used in many ways and combined with many
kinds of foods. All the different types of cheese are made from it. Meat,
vegetables, and cereals may be cooked in it. It is used as a basis for many
sauces. Such sauces may be combined with eggs, with meats, or with
vegetables; it is used in puddings and in frozen desserts; it is used for
soups and for drinks like cocoa and coffee; it is combined with cereals;
it is used in combination with many foods, as in custards, in cakes, and
in quick breads.
Milk from different animals is used for food, but in this country unless
the source of the milk is mentioned it is understood to be cow's milk.
Composition of Milk
Milk from different animals varies somewhat in the proportion of the
different constituents. All milk contains a high proportion of water, cow's
milk averaging about 87 per cent. The milk from different breeds of cattle
varies considerably in composition. The milk of individual cows of the
same breed also varies in the proportion of the different constituents. This
may be partly due to environment, partly to inheritance, and partly to
individuality. Milk may vary particularly in fat content from one milking
to the next. The percentage of fat increases during the milking period ; that
is, the first milk obtained is not so rich in fat as the last portions of milk.
The fat varies for different breeds from about 3.5 per cent for Holstein
to about 5 per cent for Guernsey and Jersey.
The protein varies from about 3.3 per cent for Holstein to 4.0 per cent
for Guernsey and Jersey. It parallels the fat content somewhat, being
highest in the breeds having a high fat content and lowest in those having
a low fat content.
The lactose does not vary so much with the different breeds as the fat
and protein. The lactose content is from about 4.65 to 5 per cent.
The ash varies from about 0.68 to 0.75 for the different breeds.
Constituents of Milk
Chemical and Physical Properties
The constituents of milk that are most important in food preparation
are enzymes, vitamins, pigments, salts, sugar, fat, and proteins.
293
294 MILK AND CHEESE
Enzymes. The enzymes of cow's milk are reported as follows by
Rogers; proteinases, lactase, diastase, lipase, salolase, catalase, peroxidase,
and aldehydrase. Rogers states that the proteolytic enzyme, galactase, brings
about slow decomposition of milk proteins into peptones, amino acids, and
ammonia.
Vitamins. All the vitamins recognized at the present time are contained
in milk. Some are present in comparatively large and others in smaller
amounts.
Pigments. The appearance of milk is white. This is due to light rays
reflected by the colloidally dispersed constituents of the milk, the calcium
caseinate, and calcium phosphate.
Milk contains two classes of yellow or orange pigments. The water-
soluble pigment, which imparts a yellow color with a green fluorescence
to the whey of milk, was formerly called lactochrome. A name recently
suggested for this pigment is lactoflavin. It is regarded as one flavin of a
specific group, collectively to be called lyochromes. It is possible that lacto-
flavin is composed of more than one pigment. Rogers says "lactoflavin
forms compounds with saccharides, proteins, and purines (uric acid). These
compounds possibly either occur naturally in milk or readily form during
isolations, thus accounting for the several lactoflavins isolated from milk."
It is probable that the pigment lactoflavin is one of the five fractions of
vitamin G (B L >). Milk is relatively rich in this vitamin.
A fat-soluble pigment, carotene, found in the fat gives the milk a more
or less yellow tinge, which is more pronounced as the fat particles become
more concentrated and form cream. The group of pigments called caroti-
noids, w r hich include carotene, xanthophyll, and related pigments, has been
described in the chapter on fruits and vegetables. The chief pigment of
butter fat is the carotene, but little xanthophyll being found. The depth of
color depends upon the amount of pigment present. The color of carotene in
solution varies from yellow to orange and to a deep red-orange as the
concentration increases. The amount of carotene found in the butter fat
depends upon the extent of carotene in the food of the cow. Green grasses,
hay cured to retain its green color, green corn, and carrots are rich in
carotene. The carotene content of milk fat is less rich during the winter
months, if the food of the cow is poor in carotene during this period. Only
in cow's milk is the fat extensively pigmented. With the exception of
the fat of human milk, w r hich is often pigmented, the fat of the milk of
other animals is either devoid of or contains little pigment.
Salts. Milk contains salts of potassium, sodium, magnesium, calcium,
phosphates, chlorides, and citrates. Traces of sulfates and carbonates are
found. Iron is present in small amount. Iodides are also found in small
amounts, the amount being greater in some localities than in others. Iodides
may be easily transmitted from the feed to the milk. Supplee and Bellis
have found copper to average about 0.52 part per million in freshly drawn
milk. Brickner has reported that milk contains 3.6 to 5.6 parts of zinc per
FAT 295
million parts of milk. Manganese in normal milk averages 0.02 to 0.06
parts per million. The greater part of the sulfur is found in the milk pro-
teins. Barger and Coyne state that part of the sulfur in milk is found in
the amino acids methionine and cystine of the proteins, but that all of the
sulfur is not accounted for.
The salts of milk are found in milk in solution, in the colloidal state,
and in combination with the proteins. The exact chemical combinations
of the different salts in the milk are not fully determined. For this reason
different authorities report different salt combinations. Thus formulas
imply definite combination, whereas there is a complex salt equilibrium in
milk, which has not been satisfactorily worked out. The citrates, the com-
binations of which may be trisodium and tripotassium citrate, tricalcium
and trimagnesium citrate, are probably entirely in solution. The possible
chlorides of potassium, sodium, and calcium are also in solution. Some
authorities believe that the phosphates are present chiefly as dicalcium
phosphate, CaHPO4,' others believe that tricalcium phosphate, Ca3(PO4)2,
is the principal phosphate combination. The phosphates are partly in solu-
tion, with the greater portion in colloidal dispersion. When the particles
of dicalcium phosphate are heated they become aggregated and partially
precipitated.
Calcium and magnesium are in combination with the casein to form
calcium and magnesium caseinates. Zoller states that there may be traces
of sodium and potassium caseinates.
Lactose. The solubility of lactose and its properties may be found in
the chapter on sugar. It is caramelized by heat at rather low temperatures.
Fat. Butter fat is composed of glycerol and fatty acids. Fatty acids of
both the saturated and unsaturated series are present. The relative per-
centage of the unsaturated fatty acids varies with the feed, averaging
higher in summer than in winter. Dean and Hilditch state that the oleic
and linoleic acids increase by 4 per cent (mols), with a parallel diminution
in butyric and stearic acids when cows return to pasture. They also report
that with increased age of the cow the unsaturated acids increase at the
expense of palmitic acid, which was lowered from 29 to 22-23 per cent by
weight of the total fat in the four years of observations made on milk from
the same group of cows. The saturated fatty acids are butyric, caproic,
caprylic, capric, lauric, myristic, plamitic, and stearic. Arachadonic acid has
been reported absent by some investigators. Butter fat contains a higher
proportion of the first-named saturated acids than other food fats. The
first ones in the series are quite volatile with steam, the volatility decreasing
with increase in molecular weight of the acid. Hence, when butter is heated
for several minutes, the percentage of the lower saturated fatty acids may
be decreased. The unsaturated fatty acids include oleic, linoleic, and
arachidic.
Formerly it was thought that the particular flavor of butter was due
to the greater proportion of the lower saturated fatty acids, but now it is
296 MILK AND CHEESE
known that butters with satisfactory flavor and aroma (Michaelian,
Farmer, and Hammer) contain considerable quantities of acetylmethyl-
carbinol plus diacetyl. The acetylmethylcarbinol in a pure condition is odor-
less, but by bacterial action it is changed to diacetyl, which in concentra-
tions of 0.0002 to 0.0004 per cent in or added to neutral butter gives a
characteristic aroma.
Size of fat globules. The fat in milk is found in small globules. These
fat globules which are microscopic in size are suspended in the milk. They
vary in size from 0.10/x to 22.0/x. Most of the globules are less than lO^u,
and average about 3/x, in diameter. The size of the fat globules varies
( 1 ) with different breeds, being larger in milk from Jersey and Guernsey
than in milk from other breeds, (2) with the lactation period, decreasing
in size with length of the lactation period, and (3) with feed. Dry feed
tends to decrease the size of the globules, succulent feed to increase their
size.
Creaming. The specific gravity of the fat globules is less than that of
the fluid of the milk. Hence there is a tendency for them to rise to the
surface to form a cream layer. The extent of creaming depends upon several
factors, such as the size of the fat globules, temperature of the milk, acidity,
physical state of the fat, etc. Creaming occurs more rapidly in milk when
the fat globules are quite large than when they are smaller. In rising to
the top of the milk the globules of fat clump together, and this clumping
increases the tendency for them to rise to the surface of the milk. As the
larger clumps rise they may carry many of the smaller globules to the
surface. Therefore, clumping not only aids the completeness of creaming
but also the rate, for the rate is more rapid when the fat particles clump
quickly. Rogers states that the factors affecting clumping are "temperature,
the acidity, the fat content and its degree of dispersion, the degree of
agitation, and the fluidity of the system. The fat content, the degree of
agitation and the fluidity of the system determine the probability of col-
lisions of the globules." The tendency of the fat globules to clump is
greatest when the milk is cooled rapidly to 7 to 8C., but if the fat
globules become solid at the low temperature before creaming is allowed to
take place the rate of creaming is retarded. The temperature that favors
clumping is also best for whipping the cream. Most cream is separated
from the milk by mechanical means. The fat particles left in the milk
after separating the cream are those less than 1/x and those between 1 and
2/j, in diameter.
Butter. The fat globules in cow's milk are suspended in the milk and
thus do not form a permanent emulsion, though they may be so reduced
in size by homogenization that they form a permanent emulsion. Of the
different theories formulated for explaining the manner in which emulsions
are stabilized the adsorption film theory is usually connected with milk.
Substances that lower surface tension tend to collect at the interface be-
tween two non-miscible systems. Proteins tend to lower the surface tension,
FAT 297
hence tend to collect at the interface. The layer or film around the fat
globules probably consists of adsorbed calcium caseinate, with some lactal-
bumin, globulin, and calcium phosphate. This membrane may be weakened
or broken in various ways. When milk is heated slowly, the membrane
surrounding some of the fat globules may be broken and a number of
globules may coalesce. Sometimes milk that has been heated and then
cooled has a more oily appearance due to this coalescing of the fat globules.
The membrane surrounding the fat particles may be broken by mechanical
agitation. Formation of butter in churning is brought about in this manner.
There are two theories regarding butter formation. One is that the
emulsion is reversed from the type found in the milk and that the butter
is a water-in-fat emulsion. The other view is that butter is formed by
packing the fat globules into a compact mass, and that water and air
are enmeshed during this process. Temperature and the formation of a
foam are both important in churning. At a temperature above 65 C. there
is no aggregation of fat particles. Below 65 the tendency to clump in-
creases and is at a maximum at 7 to 8C. A favorable temperature for
butter formation is below 24 and above 10C. At temperatures below
4C. the fat globules do not adhere to each other and aggregation does
not take place. At temperatures above the melting point of butter, no
butter is formed.
The fat particles tend to clump at the liquid/air interface, so that air
beaten in during the churning process accelerates clumping of the fat.
Butter may be churned from sweet or sour cream. The flavor of butter
from the sweet cream is milder and different from that of the sour-cream
butter. Many housekeepers prefer the sweet-cream butter for table use and
the sour-cream butter for cooking.
The adsorbed films surrounding the fat globules may also be destroyed
by the addition of acid or alkali. It is by these methods that the fat is
set free for a quantitative determination. In the Babcock.test, acid is used
for liberating the fat globules ; in the Hoyberg test alkali is used. The Bab-
cock, or some modification of it, is the one usually employed in estimating
the fat content of milk and cream.
Protein. The chief proteins found in milk in order of their decreasing
amounts are casein, lactalbumin, and lactoglobulin.
Casein. Casein belongs to the group of phosphoproteins. The form in
which the phosphorus exists in the casein is not definitely known, but it is
believed to be present in the form of combined phosphoric acid. Casein
forms about 3 per cent of cow's milk.
At its isoelectric point, which is />H 4.6, casein is nearly insoluble in
water. Casein is amphoteric and forms salts with acids and alkalies. Fresh
milk has a reaction of about /H 6.6, so that the casein is present in the
milk as salts of bases and is found as calcium and magnesium caseinates.
All the alkali caseinates are soluble in water, though the salts of the
alkaline earths are less soluble than the alkali ones. Loeb states that below
298 MILK AND CHEESE
pH 4.6 the casein chloride, casein acetate, and casein lactate are very
soluble in water, but casein sulfate and casein oxalate are difficultly soluble.
According to Zoller, pure casein when heated in water begins to imbibe
water at 80 to 90C. and becomes plastic. In this form it can be molded
and shaped. Upon cooling it becomes very hard.
Casein can be precipitated from milk by bringing the milk to the isoelec-
tric point of casein. Coagulation of casein will be considered later.
Lactalbumin. The proportion of lactalbumin in milk is much lower than
that of casein. It forms about 0.50 per cent of cow's milk. Its isoelectric
point is />H 4.55. Since the reaction of fresh milk is about />H 6.6, it is on
the alkaline side of the isoelectric point of lactalbumin. Thus is it possible
that the lactalbumin is found combined as salts of bases, such as calcium
and magnesium albuminates. Osborne and Wakeman think it is uncom-
bincd. Lactalbumin is soluble in \vater, and is coagulated by heating in
solution to a temperature of about 70C. Coagulation may not be complete
at this temperature. Palmer states that the lactalbumin is more highly dis-
persed than the other colloidal constituents of the milk.
Lactoglobulln. Lactoglobulin occurs in milk in very small quantities,
about 0.05 per cent of cow's milk. Lactoglobulin is insoluble in distilled
water, but it is soluble in dilute solutions of strong bases or acids, and
in dilute salt solutions. It is coagulable by heat.
Homogenization of Milk
Globules of butter fat are suspended in the milk. They are surrounded
by films of adsorbed caseinates, albuminates, and globulinates. The fat
globules of milk are too large to form a permanent emulsion, so they grad-
ually rise to the top of the milk in the form of cream. If the milk or cream
is put through a machine called a homogenizer, the fat globules are reduced
in size. This is accomplished by using pressure and forcing the milk or
cream through small openings. Homogenized milk or cream may form a
stable emulsion if the fat globules are reduced enough in size. Hence, when
the fat is broken into fine enough globules the cream will not rise to the
top of the homogenized milk.
The size of the fat globules after homogenization depends upon the
temperature of the milk during homogenization and the pressure used.
With increase in temperature the degree of dispersion increases rapidly
from 40 to 65C, so that the smallest fat particles are obtained at 65.
Ordinarily temperatures above 65 are not used for homogenization. The
size of the fat particles also decreases with increased pressure.
Whipped cream is stabilized by proteins. The fat globules in cream
are surrounded by films of protein substances. Homogenized cream also
has the film of adsorbed proteins around the fat particles. Clayton states
the fat particles in homogenized cream may be 1000 times greater in
number than before homogenization. Since the number of fat particles is
WHIPPING CREAM 299
increased, the amount of globulinates, caseinates, and albuminates used in
forming films is very much greater, for the surface area of the fat globules
has increased enormously.
Whipped cream is both an emulsion and a foam. The fat particles must
be surrounded by a film of protein in order to be stabilized, and the air
globules must be surrounded by a film of protein to stabilize them. In
homogenized cream most of the protein is used in surrounding the fat
globules, on account of the increased surface area of the smaller and
increased number of fat globules, and thus there is not enough left to sur-
round the air bubbles. Hence, homogenized cream seldom whips unless
protein is added for film forming.
Factors that affect the whipping quality of cream. In addition
to the protein or film forming in whipping cream, the fat content, the size
of the fat particles, the temperature of whipping, and the viscosity are
important factors. Dahlberg and Hening have studied the relation of
viscosity, surface tension, and whipping properties of milk and cream. They
have found that increased viscosity increases the whipping properties of
cream, but the lowering of the surface tension does not improve the
whipping qualities. They have reported two changes taking place during
whipping. The incorporation of air depends upon the milk proteins form-
ing the film around the air globules, and the rigidity or stiffness of the
whipped cream depends upon the clumping together of the fat particles.
The best whipping cream did not give as large a volume as some other
creams, but it had less liquid drain out of it after whipping.
Cream whips better with an increasing fat content up to 35 per cent.
The cream with the higher fat content gives more particles for clumping
and also increases the viscosity of the cream.
As the fat particles clump at the liquid/air interface, or within the
liquid, the increased rigidity they give the foam permits inclusion of more
air bubbles and extension of the films with the result that the dryness of
the foam is increased. See Fig. 31. Larger fat particles clump more readily
and thus form the structural support offered by the fat more easily. This
offers an explanation of why cream from milk containing larger fat parti-
cles, milk from Jersey and Guernsey breeds, whips more quickly than
cream containing smaller fat particles, milk from other breeds.
Aging improves the whipping qualities of cream. The viscosity increases
with aging. As a general rule, treatment that increases the viscosity increases
the whipping properties. Pasteurization tends to reduce the whipping
quality of cream.
Babcock has found that the best whipping is obtained at a temperature
of 45 F. or lower. At this temperature agitation favors the clumping
together of the fat particles. At high temperatures, both the higher tem-
perature and the agitation increase the dispersion of the fat. Above 50F.
the decrease in stiffness of whipped cream is in direct ratio to increase in
temperature, so that 30-per cent cream will not whip at 72F.
300
MILK AND CHEESE
Babcock found acidity up to 0.3 per cent, at which sour taste is evident,
had no effect on whipping quality. If acid was added in excess of 0.3 per
cent, whipping quality improved, whether added to fresh or aged cream,
when the amount added began to curdle the cream.
The addition of sugar to cream either before or after whipping was
found by Babcock to decrease the stiffness of the cream. For each 2 tea-
spoons added to 100 cc. (about Y\ cup) the stiffness decreased four points
on the stiffness scale. Adding the sugar before whipping the cream
decreased the volume obtained and increased the whipping time.
The denaturation or coagulation of the protein film at the air/cream
interface, increases the stiffness of the whipped cream. Since colloidal
FIG. 31. Diagram of a cross section through whipped cream. Fat globules of
the cream are shown as small black spots. Magnification about 180 (Rahn).
reactions require time, it is a better practise to add sugar to whipped cream
after, rather than before or during the whipping process. By this procedure
denaturation is more complete, which offers an explanation of why the
volume of the cream is less affected by the addition of the sugar last. The
addition of sugar lessens the stiffness and decreases the volume of the
whipped cream because it either prevents denaturation and/or peptizes
the protein film.
Reaction of Milk
Freshly secreted milk is nearly neutral to litmus. The reaction varies
slightly but has an approximate pH of 6.6. The freshly secreted milk con-
tains carbon dioxide. The amount of this gas in the milk decreases during
milking and the subsequent handling of the milk, while the percentage of
oxygen and nitrogen increase. For this reason the titratable acidity decreases
for a time in milk exposed to the air. Confined milk does not show as great
RENNET COAGULATION 301
a decrease in titratable acidity as the exposed milk, for the percentage of
carbon dioxide lost is smaller.
Effect of heating milk on acidity. When milk is heated at the boil-
ing point or at temperatures above or near the boiling point the titratable
acidity at first decreases owing to the loss of carbon dioxide, and then
increases. Whittier and Benton report that the hydrogen-ion concentra-
tion increases continuously. They find the hydrogen-ion increase and the
later increase in titratable acidity is due to the formation of acids from
constituents of the milk. The amount of acid produced depends upon the
time and temperature of heating, a greater amount of acid being produced
with a longer heating period and with higher temperatures. From their
experiments they conclude that the acid is produced from the lactose of the
milk. They have shown that, the greater the concentration of lactose pres-
ent, the greater the amount of acid formed at a definite temperature and
for a definite time.
Coagulation of Milk
Under certain conditions, the addition of alcohol as well as the appli-
cation of heat may cause coagulation of milk. Milk may be coagulated by
the addition of rennin or by bringing the acidity of the milk to the isoelec-
tric point of the casein. When milk is combined with other foods, the salt
content of the food or the tannin content of the food may be factors that
aid coagulation.
Alcohol coagulation. The addition of 70 per cent alcohol to milk may
cause coagulation. As the pH of the milk decreases, it becomes susceptible
to alcohol precipitation, though this varies with different milks. Usually
the milk is precipitated by alcohol while it is still stable to heat and
sterilizing temperatures. Some freshly secreted milk is coagulated by
alcohol, but this milk is usually abnormal in some way. About 2 cc. of
alcohol are added to an equal quantity of milk for the test. Casein is
precipitated by alcohol as calcium caseinate, calcium is not released as by
acid coagulation.
Rennet coagulation. Milk may be coagulated by the addition of
rennet. Rennet is an extract that is usually obtained from the inner lining
of the stomachs of calves and lambs. The rennet contains an enzyme called
rennase or rennin.
The clotting of the milk is generally believed to be the direct action of
the rennin on the casein. But the manner in which these changes is pro-
duced is not fully understood. A very small amount of rennin is capable
of coagulating a large amount of milk. At favorable or optimum hydrogen-
ion concentrations for clotting, 1 part of the fairly pure enzyme prepara-
tion is able to coagulate 3,000,000 or more parts of milk.
Mechanism of clotting. It is usually stated that the casein is changed to
paracasein by the action of the rennin. It is also often stated that the
302 MILK AND CHEESE
clotting is brought about in two steps, the first being the action of rennin
on the casein and the second the precipitation of the changed casein. Rogers
reviews the many theories of rennin coagulation. Some investigators claim
the changes are purely chemical; others maintain the rennin affects only
the physical state of the calcium caseinate. However, if the change can be
explained on the basis of colloid chemistry, it is probable that absorption
and the electric charge play an important role in the process. Rogers states
that Hammarsten regards casein in milk as a calcium caseinate-calcium
phosphate complex. "As a matter of fact the compound called calcium
caseinate is most probably a true calcium phosphocaseinate, if, as seems
likely, the second and third hydrogens of the orthophosphoric acid esterfied
with certain of the amino acids in the casein molecule react with calcium.
The correct conception of the term 'calcium phosphocaseinate,' as it is
now commonly employed, is that of a colloidal calcium phosphate (or
phosphates) sol protected by a calcium caseinate (or caseinates) sol in a
manner as yet imperfectly understood." The stabilization of sols is best
explained by the theory of Helmholtz, i.e., each colloidal particle is sur-
rounded by an electrical double layer. "In the case of negatively charged
sols, in which class calcium caseinate and calcium paracaseinate evidently
fall, the outer layer consists of hydrogen ions. If these are replaced by a
sufficient number of positively charged ions of higher charge, e.g., calcium
ions carrying two positive charges" ; or, in other words, if these ions are
more strongly adsorbed than the hydrogen ions, the colloid particle will
readily precipitate, the rate of clotting being determined by the rate of
replacement.
Richardson and Palmer state that rennin itself may reduce the charge
of the calcium caseinate micelle and thus reduce the stability of the casein
sol. They found indications that the isoelectric point of rennin is about />H
6.9 to 7.0. Above this pH the rennin is negatively charged and below pH
6.9 it is positively charged. They found that rennin lowered the electro-
phoretic velocity of calcium caseinate and calcium phosphocaseinate micelles
when the casein sol was negatively charged and the rennin was positively
charged, but not when the rennin was negatively charged (above its iso-
electric point, />H 6.9 to 7.0). From this evidence and from the fact that
paracaseinate micelles are not affected by rennin, which agrees with the
fact that casein once coagulated by rennin has lost its sensitiveness to this
enzyme, they suggest that rennin acts by sensitizing the casein by a pre-
liminary reduction of the electric charge on the casein micelles.
During the clotting of the milk, aside from the consistency of the milk,
there is little change in its physical properties. The hydrogen-ion concen-
tration does not change during the clotting process.
Factors affecting action of rennin. Several factors influence the
activity of the rennin in bringing about coagulation. These may be listed
as follows: (1) temperature for rennin action; (2) heating the milk before
the addition of rennin; (3) hydrogen-ion concentration; (4) concentration
FACTORS AFFECTING ACTION OF RENNIN 303
of casein, calcium, and phosphate ion; (5) character of cations used for
coagulation.
Temperature for rennin action. The optimum coagulation by calf rennin
is about 40 to 42C. Below this temperature coagulation is less rapid
and no clotting occurs below 10 to 15C. Also no clotting occurs above
60 to 65C. The clot is softer at low temperatures and tougher and
stringy at high temperatures. By optimum is meant the temperature at
which coagulation takes place most rapidly for a definite concentration of
rennin and milk.
Effect of previously boiling the milk upon rennin coagulation. If milk
is boiled and then cooled before the rennin is added, the rate of coagulation
is retarded and a much softer, more flocculent clot is obtained. Pasteuriza-
tion also affects the rate of coagulation of the milk and the type of clot
formed by rennin but not to the extent that boiling does.
Richardson and Palmer found by electrokinetic evidence that heat in-
creased the electric charge on the casein micelles or the cataphoretic velocity
of the casein solution. The fact that rennin does not form as firm a clot
with milk that has been previously heated indicates that rennin reduces
the charge on the casein particles but not sufficiently to form a firm clot.
This offers a colloidal explanation of why the addition of active cations
(as calcium chloride) to heated milk causes the rennin to coagulate the
milk normally.
Hydrogen-ion concentration. The reaction of the milk affects the rapid-
ity of coagulation and the character of the curd formed. Ordinarily when
the reaction of the milk is alkaline coagulation does not occur. This is
shown by the addition of a small amount of soda to milk before the addi-
tion of junket. The optimum hydrogen-ion concentration for rennin activity
has been reported to lie in the zone between />H 5.99 and 6.40.
Character of cations. In addition to rennin, cations are necessary to
bring about coagulation of milk. Because casein and calcium are so closely
involved in milk, the cation calcium is important in bringing about coagula-
tion. Hence, Rogers states that it is to be expected that the concentration
of both casein and calcium markedly affect both the rate of coagulation and
the character of the clot. If milk is diluted with sufficient water, clotting
is both delayed and incomplete, the clot being soft. If calcium chloride
is added to the water, diluted milk clotting properties are restored, which
suggests that the concentration of calcium ions is more important than
that of the casein ions.
Rogers states that any metallic ion can replace the calcium in coagulation.
However, it is generally accepted that the sodium and potassium salts of
paracasein are soluble. Monovalent ions are less effective than divalent
ones in replacing the calcium. Rogers reports that all monovalent ions did
not bring about coagulation in some instances. The divalent ions were not
all equally effective, calcium and barium being more efficient than mag-
nesium.
304 MILK AND CHEESE
Sugar. Sugar tends to prevent the coagulation of milk by rennin.
Coagulation of milk by acid. Kruyt states that there are some
proteins that are not sufficiently hydrated to be stable by hydration alone.
He cites casein as an example of a protein "which can exist either in acid
or in an alkaline solution, but does not dissolve in water, with the con-
sequence that the sol ordinarily flocculates when neutralized." Either
the acid produced during fermentation or acids added to milk precipitate
the casein. The casein is least soluble at its isoelectric point />H 4.6. If
enough acid is added to lower the />H below 4.6, casein salts, such as
casein chloride or casein lactate, are formed. If these salts are soluble, the
casein goes into solution. Hence the largest yield of precipitated casein is
near the isoelectric point.
Fermentation of milk. Fermentation, or the production of lactic acid
from lactose by bacteria, takes place in milk that is allowed to stand under
favorable conditions. Rogers states that true lactic acid fermentation is
brought about by the Streptococcus lactis and certain other organisms,
lactic acid being the principal end-product, other products being present
in only small amounts. In mixed lactic acid fermentation, or when other
organisms in addition to S. lactis are present, the end-products may include
acetic, propionic, lactic, succinic, formic, and butyric acids, carbon dioxide,
hydrogen, acetone, and ethanol. As fermentation increases, an acidity is
reached at which the action of most bacteria is suppressed. When fermenta-
tion is checked at pH 4.8 to 5.0, the bacteria consists chiefly of Strepto-
coccus lactis.
The rate of fermentation depends chiefly upon the temperature at which
the milk is held. At low temperatures, on account of retardation of bac-
terial action, it takes place slowly. Rogers states that fermented milk,
allowed to stand at a fairly high temperature, undergoes a second lactic
acid fermentation brought about by the Lactobacillus bulgaricus organ-
isms. Some of these types of bacteria form a high percentage of acid and
the hydrogen-ion concentration may reach pH 3.23.
Changes occurring during acid precipitation. During fermentation chem-
ical and physical changes occur in the milk. The flavor becomes acid. The
calcium caseinate is changed to casein. During this process calcium is split
off and forms soluble calcium lactate. In addition some dicalcium phos-
phate is converted into monocalcium phosphate. Curdling or clotting occurs
when the acidity reaches about pH 5.3. During the clotting process the
hydrogen-ion concentration does not increase. Milk clotted by fermenta-
tion is often called clabbered milk. Its flavor and aroma may vary, depend-
ing upon the types of bacteria producing the fermentation. Fermented
milk may be used for drinking, for cooking, and for cottage cheese.
Cheese, such as cottage cheese, when clotted by acid coagulation, loses a
large proportion of its calcium. The calcium salts become soluble more
rapidly than the phosphorus ; hence a larger proportion of the calcium than
of the phosphorus is lost in the whey. Casein precipitated by rennin retains
HEAT COAGULATION 305
most of its insoluble salts, hence has a larger proportion of calcium than
the acid precipitated casein.
Heat Coagulation. The term heat coagulation refers to the so-called
"denaturation" of the protein, by which it is rendered insoluble.
Lactalbumin. Lactalbumin has temperatures for heat coagulation similar
to that of egg albumin. The lactalbumin forms a flocculent precipitate,
whereas egg albumin forms a firm coagulum. Rupp has reported the fol-
lowing amount of lactalbumin coagulated when heated for 30 minutes.
Temperature, Albumin rendered insoluble,
C. per cent
62.8 0.00
65.6 5.75
68.3 12.75
71.1 30.78
Casein. Casein is not coagulated by heat at ordinary temperatures or
when heated for short periods, though the heating may alter the casein.
Rogers states that it is necessary to heat milk about 12 hours at 100C. to
bring about coagulation. It takes approximately 1 hour at 135C. and
approximately 3 minutes at 155C. The time and temperature vary some-
what with different milks.
The rate of coagulation depends upon the concentration of the casein as
well as the time and the temperature of heating. Rogers states that
evaporated milk, containing twice the concentration of solids-not-fat in
normal milk, and thus a higher concentration of casein, requires about 60
minutes for coagulation at 114.5C., 10 minutes at 131C., and 7500
minutes at 80C.
Rogers and Palmer both state that, in the evaporated-milk industry,
the forewarming of milk prior to processing increases its stability to heat.
"Rapid improvement in resistance to heat coagulation results in increase
in temperature for prewarming up to 90 to 100C. Above 90C. the
change is very small, but in some cases can be effected with increases in
temperature up to 120C. for 10-minute periods of forewarming. When
time is chosen as the variable, improvement may be noted with increases in
the time up to 30 minutes at a temperature of 95 C. At higher tempera-
tures the same improvement may be effected in shorter periods of time."
Fat. Rogers states that fat particles in relatively large aggregates may
act as nuclei about which coagulation of the casein can proceed. In un-
homogenized milk the fat affects the coagulation time and temperature but
slightly. But when a milk of higher fat content is homogenized the fat
clumps may act as nuclei about which the casein may gather during heat-
ing. With increase in homogenization pressure as well as fat content, other
conditions being the same, a marked decrease in stability to heat is noted.
In homogenized milk it was found that the maximum stability to heat
coagulation occurs if homogenization is carried out at 80.
306 MILK AND CHEESE
Rogers adds that the feathering of some homogenized cream when
added to coffee may be caused by using too high homogenization pressure,
thus reducing the stability of the cream to heat.
The role of salts in heat coagulation of milk. In heat coagulation of
milk, the milk salts play an important role, for the salt equilibrium is
altered by heat. When milk is boiled precipitation of part of the calcium
phosphate occurs. Sommer and Hart have concluded that salts are the
main factor in heat coagulation of fresh milk. Electrolytes have a marked
effect upon the stability of colloids. In precipitating a hydrophilic colloid
divalent and trivalent ions are generally more effective than monovalent
ones. In the milk are found the monovalent cations, sodium and potas-
sium ; the monovalent anion, chlorine ; the divalent cations, calcium and
magnesium; and the trivalent anions, phosphate and citrate. Sommer and
Hart concluded that the coagulation of milk on heating may be due to an
excess or a deficiency of calcium and magnesium. They explain this as
follows. "The casein of the milk is most stable with regard to heat when
it is in combination w^ith the calcium. If the calcium combined with the
casein is above or below this optimum, the casein is not in its most stable
condition. The calcium of the milk distributes itself between the casein,
citrates, and phosphates chiefly. If the milk is high in citrate and phosphate
content, more calcium is necessary in order that the casein may retain its
optimum calcium content after competing with the citrates and phosphates.
If the milk is high in calcium there may not be sufficient citrates and
phosphates to compete with the casein to lower its calcium content to the
optimum. In such cases the addition of citrates or phosphates makes the
casein more stable by reducing its calcium content. The magnesium func-
tions by replacing the calcium in the citrates and phosphates."
Heat coagulation of casein endothermic. Leighton and Mudge have
shown that an endothermic reaction accompanies the appearance of visible
curds when milk is coagulated by heat. This is accompanied by precipita-
tion of calcium and magnesium as phosphate and citrates.
A similar reaction occurs in custard. In cooking custard, the ingredients
of which are milk, egg, and sugar, the temperature drops or does not rise
for a period of time during coagulation or setting of the custard, a condition
particularly noticeable just before curdling takes place.
Coagulation of milk by cooking meat or vegetables in it. Fresh
milk is seldom coagulated by heating for home use. The temperature
attained in ordinary heating is not great enough to cause coagulation, nor
is the milk heated for the long period required for coagulation at boiling
temperatures. But with the addition of other foods to milk in food prepara-
tion, coagulation often occurs with a very short period of heating. One
of the factors in this coagulation is undoubtedly the salt content of the
food added to the milk as well as the salt content of the milk. The balance
of the milk salts for greatest stability may be upset and coagulation occurs
when the food is heated in the milk.
COOKING OF VEGETABLES IN MILK 307
Cooking of meat in milk. Ham is often baked in milk. Sometimes
pork chops are floured, seared in fat, and then baked in milk. Other meats
and fish are sometimes baked or cooked in milk. Often curdling of the
milk occurs, and the appearance of the meat, owing to adherence of curds
of milk, is not attractive. Thus it is desirable to prevent curdling. Among
the causes of curdling are the temperature at which the meat is cooked,
the salt content of the food cooked in the milk, the manner in which the
milk is added to the meat, and the reaction of the milk.
The higher the temperature at which the meat is cooked the greater
the tendency to curdle. Larger curds are also formed at higher tempera-
tures. The temperature to which milk must be heated to bring about curd-
ling is high, so this cooking temperature alone is not sufficient to bring
about the coagulation. Even when the meat is cooked in an oven at a high
temperature, the liquid portion does not reach a higher temperature than
boiling. It is possible that the acidity is increased during cooking, but the
resulting />H of the meat-milk broth is changed very little from that of the
original milk or from that of the meat broth when the meat is cooked in
water. Thus it seems that the heating and the acidity developed during
cooking do not alone bring about coagulation.
The salt content of the food cooked in the milk probably influences the
coagulation, and this combined with the heating, the temperature of heat-
ing, the acidity developed, and the altering of the casein by heat are suf-
ficient to cause curdling. Sodium chloride has some effect, for curdling is
more likely to occur when the meat cooked in the milk is a cured or salted
one than when fresh meat is used.
Curdling may be prevented by the addition of soda, about 1/16 teaspoon
per cup of milk. From this it appears that the reaction has some part in
the coagulation. The soda may combine with other salts that tend to bring
about coagulation or the coagulation may be prevented by the slightly
alkaline reaction. A slightly alkaline reaction also prevents coagulation by
rennin and by fermentation.
If a portion of the milk is added to the meat when cooking is first
started and the rest of the cold milk added gradually to the meat during
the cooking period, curdling is less likely to occur. The addition of acid
foods, such as prepared mustard, which may contain vinegar, or apples
and pears to be baked with the meat, would tend to increase the tendency
to curdle. Evaporated milk has less tendency to curdle than fresh milk,
which may be due to the previous heating.
Cooking of vegetables in milk. Milk usually does not curdle when
cabbage, chard, spinach, or cauliflower is cooked in it. But it is likely
to curdle when asparagus, string beans, peas, and carrots are cooked in it.
Asparagus usually curdles the milk after a few minutes of cooking. There
are several factors that may aid in bringing about coagulation of the milk.
The slight acidity of some vegetables combined with the heating of the
milk may tend to bring about coagulation, but the acidity is not usually
308 MILK AND CHEESE
great enough, nor the boiling temperature high enough, nor the boiling
long enough continued for these factors to be very important. The salt
and the tannin contents of the vegetables are probably the principal causes
of coagulation. Some vegetables contain larger amounts of tannin than
others. Tannin is a dehydrating agent and brings about denaturation of
hydrophilic sols, like gelatin, starch, and agar-agar. After denaturation the
hydrophile is sensitive to small amounts of electrolytes and precipitation
occurs readily. Kruyt states that tannins do not bring about dehydration
of the protein in an alkaline medium. Hence the addition of soda in small
amounts to the milk in which the vegetable is cooked prevents coagulation
of the milk. Tannins lower the surface tension, which results in foaming
of vegetables containing tannin when they are cooked in water. It is rather
interesting that the vegetables that usually foam the most when cooked
in water are the ones that have the greatest tendency to coagulate milk.
Totnato soup. When tomatoes are combined with milk to make cream of
tomato soup, coagulation may occur. The acidity of tomatoes varies some-
what, but is about />H 4.4 to 4.6. If the amount of tomato added to the
milk is great enough to lower the />H of the mixed milk and tomato to
4.8 to 4.6, the casein is precipitated without heating. This may happen if
the milk is already fairly acid.
Since a longer time of heating milk increases the tendency to curdle it is
preferable to heat tomato soup for only a short time. Heating slowly also
increases the tendency to curdle, which may be due to the longer time
required. In Experiment 55 in the laboratory outline several different
methods of combining the tomato juice and milk are given. The tomato
is usually added to the milk by stirring, for in this way the milk is diluted
with a smaller amount of acid substance during the first part of the mixing.
There is less tendency to curdle when the hot tomato is added to cold milk,
than when the cold tomato is added to hot milk. Probably the slight
denaturation brought about by heating the milk may partially account
for this. Occasionally some milk is acid enough and the tomato is acid
enough to cause curdling with all methods of combining unless soda is
added. At other times curdling does not occur with any method of com-
bining as outlined in this experiment.
Fruits and milk. When cream is added to fruit, clotting often occurs.
This is usually due to the acidity of the fruit, but may also be due to an
enzyme in it. Raw pineapple contains an enzyme, bromelin, that brings
about clotting of milk. However, the pineapple juice not only brings about
clotting but also peptization, for after a time the clot formed is less firm
and the flavor is similar to that of peptized meat.
Boiling and Heating of Milk
The physical and chemical properties of the constituents of milk account
for the behavior of milk during its use in food preparation. Thus sub-
SUGAR REACTIONS WITH PROTEINS OF MILK 309
stances that lower surface tension become concentrated in the liquid/air
interface. Proteins lower the surface tension of aqueous sols, hence accu-
mulate in the surface. When milk is heated in an open pan, a scum or skin
forms over the surface of the milk. At first this skin is rather thin and
mobile but is gradually altered so that it becomes tenacious and tough
enough to be removed with a stirring rod or spoon. This scum has been
said to contain coagulated albumin and globulin. Tinkler and Masters
state that if the scum is removed as formed, the total amount of protein
that can be removed exceeds the total amount of albumin and globulin in
the milk.
When foods are cooked in milk the milk not only foams readily but the
scum tends to hold the steam formed in heating the milk; it is because
of this that the milk "boils over" so readily.
Sugar Reactions with Proteins of Milk
Ramsay, Tracy, and Ruehe investigated the substitution of dextrose for
sucrose in sweetened condensed skim milk. They found the objections to
using dextrose were (1) a brown discoloration, (2) a physical thickening,
and (3) crystallization of the dextrose during storage. The last objection
could be remedied by using 50 per cent dextrose and 50 per cent sucrose.
The progressive thickening during storage at high temperature was caused
by action of the dextrose on the casein and albumin of the milk. During
this investigation they found additional evidence that sugars react with
proteins. When dextrose, lactose, or levulose was heated with skim milk or
freshly precipitated casein, a dark brown color formed in the product.
When the sugars were heated in distilled water solutions to 250F. for
30 minutes no caramelization occurred. Neither did darkening occur when
albumin or casein was heated in water solution. But when the milk,
albumin, or casein was heated with lactose or dextrose, a brown dis-
coloration occurred. As the temperature was raised the dextrose and
casein became so firmly attached to each other that no amount of washing
could remove the sugar. Most of the biruet action of the skim milk was
lost. The results were explained on the basis that a protein-sugar complex
of glucosidal nature was formed.
On heating amino acids with dextrose highly colored products were
formed, the reaction probably being a condensation of an amino acid with
an aldehyde or ketone group of the sugar. The very stable linkage of the
aldehyde group of the dextrose and the ketone group of the fructose in the
sucrose molecule is cited to explain the failure of sucrose to form condensa-
tion products with casein, albumin, or amino acids. It was found that as
the reaction became more alkaline the appearance of the brown color was
more rapid. The increased alkalinity was said to favor the change of the
sugar from a lactone to a free aldehyde form, the free aldehyde acting with
the amino acid or -NH2 groups of the protein. If the />H was much
310 MILK AND CHEESE
above 7 the milk was almost black. Hence, the sugar used, the reaction,
and temperature all influenced the development of the brown color. The
length of heating in connection with the temperature was important as
relatively high temperatures for a short period gave only slight develop-
ment of the brown color. It is almost impossible to retain the natural color
of fresh milk in the condensed milk products, for some brown discoloration
occurs in the unsweetened and sweetened product whether made from
whole or skim milk.
Whittier and Benton had shown that the hydrogen-ion concentration
increases at a rate which is the function of the lactose concentration and
the time and temperature of heating. Or, in other words, when milk is
heated for a sufficient time at high enough temperatures the lactose is
decomposed with formation of acid products. Hence, when milk is heated
with sucrose the increasing acidity inverts some of the sucrose to dextrose
and levulose, with the development of a brownish color. One example of
this is in the cooking of caramels, more brown color developing with long
slow cooking of the sucrose and milk. Another instance where this is used
to advantage is in making caramel pudding by boiling, in the can, sweetened
condensed milk for three hours or longer. The can and contents are chilled.
On opening the can it is found that the contents have developed the brown
color of caramelized products and are thickened to the consistency of a
pudding.
This combination of sugar with milk proteins to form a thickened
product is interesting in view of the fact that sucrose, dextrose, and levu-
lose prevent the heat coagulation of egg albumin.
The housewife also makes use of the effect of acid on sweetened con-
densed milk. If about ^2 cup of lemon juice is stirred into the contents of
a can (about \ l /2 cups) of sweetened condensed milk, the mixture thickens
to a consistency that can be used for a pudding or pie filling and may be
thinned with water to a desired consistency. The explanation of the
thickening lies in the action of the acid on the complex sugar-protein
combination.
Cheese
Definition. The Food and Drug Administration defines cheese, in the
regulatory announcements, as "a product made from curd obtained from
the whole, partly skimmed, or skimmed milk of cows, or from milk of
other animals with or without added cream, by coagulating with rennet,
lactic acid, or other suitable enzyme or acid, and with or without further
treatment of the separated curd by heat or pressure, or by means of ripen-
ing ferments, special molds, or seasoning."
Classification of cheese. Cheese may be classified in many ways as
(1) method by which the curd is produced, i.e., acid or rennet coagula-
tion, (2) source of the milk, from cow, sheep, or goat, and (3) the
COAGULATION OF MILK FOR CHEESE 311
texture and consistency of the cheese, i.e., whether soft, semi-hard, or hard.
Many other classifications might be used but none of them are entirely
satisfactory.
Doane and Lawson list and describe nearly 300 cheeses. They state
there are probably about 18 distinct varieties of cheese.
For purposes of discussion, Rogers classifies cheese as follows:
Soft Hard
Unripened Semi-hard
Cottage Ripened by molds
Cream Gorgonzola
Neufchatel Roquefort
Ripened Stilton
Ripened by molds Ripened by bacteria
Camembert Brick
Brie Munster
Ripened by bacteria Very hard
Limberger Without gas holes
Liderkranz Cheddar
Edam
Gouda
With gas holes
Emmenthal
Swiss
Parmesan
Composition of cheese. From the standpoint of quantity the prin-
cipal constituents of cheese are casein, fat, and water. In addition it
contains various salts, and unless heated to pasteurization temperatures
various organisms such as bacteria and molds. Different types of soft
cheese may contain from 40 to 75 per cent of water, hence this type does
not keep long. Hard-type cheeses usually average 30 to 40 per cent
moisture. The soft types may contain from 13 to 21 per cent of protein
and from 0.5 to 50 per cent of fat. Hard types contain from 20 to 45 per
cent protein and 19 to 40 per cent fat.
Coagulation of milk for cheese. Coagulation may be brought about
by rennet or acid. Rennet-formed curds are more elastic, the acid ones
more sticky. In acid-formed curds more of the calcium salts are split off
from casein, forming calcium chloride which is soluble in the whey. Rennet-
coagulated cheeses of cheddar types retain about 80 per cent of the calcium
of milk, whereas soft cheeses retain about 20 per cent.
The temperature for coagulation varies with the type of cheese desired.
In general, the lower the temperature the softer the curd. Curds formed
at 21 to 25 C. are used for some soft cheeses. Cheddar cheese has a
firmer curd and the milk is brought to 30C. before the starter and rennet
are added. Temperatures as high as 48C. may be used for some cheese,
312 MILK AND CHEESE
the curd produced being distinctly tough and somewhat rubbery and
elastic.
Making cheese. The essential steps in making cheese are: blending
the particular type of milk desired ; bringing the milk to a definite tempera-
ture ; adding lactic acid culture for types of cheese that need greater
hydrogen-ion concentration when the rennet is added (acid cultures are
added to cheddar types, but not to Swiss) ; adding vegetable color, if
cheese is to be yellow, omitting if cheese is to be American white; and
adding the rennet. After coagulation the curds are cut to the definite size
for the type of cheese desired. Small curds retain less moisture within the
curd but the whey does not drain so well from the curd. The next step
is stirring the curd gently to facilitate draining of the whey. The curd is
then ditched, salted, put in molds lined with cloth, and pressed into defi-
nite shapes as Longhorms, Prints, Daisies, Flats, Twins, and Cheddars.
After being pressed the cheese may be soaked in salt brine or dry salt may
be rubbed on the surface. Sometimes no additional salting occurs. Soft
unripened cheese is not cured ; but after being pressed or molded other
types are placed on shelves in caves or specially constructed curing rooms
to ripen. In the latter ventilation, humidity, and temperature may be care-
fully controlled according to the type of cheese. The curing period varies
for different types of cheese and for the same type. For example, Cheddar
may be cured from 2 or 3 months to 2 years. With longer curing a
sharper, richer, and fuller flavor is developed.
Cheese, after being cured, is often blended for uniform flavor, texture,
and body.
Secondary heating of the curd. A secondary heating of the curd is
necessary with most hard and semi-hard cheeses. Making Emmenthal in-
volves heating to about 55 to 58C. This heating hastens the driving of
the whey from the curd, changes its texture, and often alters the bacterial
flora. The heating at high temperatures decreases the moisture content and
rennet action is checked if not wholly stopped. Various physical changes
take place during this period, the curd becoming tough, firmer, and rubbery.
In Swiss and Parmesan cheese it also acquires plasticity.
Ripening of cheese. In the process of ripening chemical and physical
changes occur in the cheese. It loses its tough, rubbery qualities and becomes
soft and mellow, sometimes almost crumbly. During this change as much
as 50 per cent of the nitrogenous constituents may be converted to soluble
forms, though the average for hard cheese is 30 per cent. These changes
not only alter the texture and flavor, but also alter the cooking quality of
the cheese, the increased solubility of the proteins increasing the ease with
which the cheese may be blended with eggs, milk, and white sauce.
Ripening is slower at lower temperatures and more rapid at higher ones.
Not only enzymes of the milk, if the milk has not been heated to a tem-
perature to destroy the enzymes, but bacteria aid in ripening of the cheese
and hydrolysis of the proteins. Some bacteria, such as lactic acid, produce
PROCESSED CHEESE 313
enzymes that split the protein. More hydrolysis occurs in the softer center
of hard cheese than near the rind. Salting affects the rate of ripening by
delaying bacterial growth, the proteins of cheese with more salt becoming
soluble at a slower rate. Salt penetrates slowly from the rind to the center
and aids in drying the cheese. Changes in the fat in the interior of most
cheese are usually negligible.
For the growth of molds and aerobic bacteria, holes must be punched
in the cheese to allow oxygen from the air to penetrate.
In the early stages of ripening Emmenthal and Swiss cheeses are soft
and become elastic. It is during this stage that the holes or "eyes" are
formed from production of gas, principally carbon dioxide, if ripening is
normal, but with more hydrogen in abnormal or early ripening. If the
cheese becomes too firm before the formation of holes is complete, checks
and cracks appear in the cheese.
Cheddar cheese in cans. The Bureau of Animal Industry (Rogers)
has announced a practical method of canning unripened Cheddar cheese.
By this method a one-way or check valve, which holds perfectly against
external pressure but with internal pressure allows gases formed during
ripening of the cheese to escape, is inserted in the lid of the can. Cheddar
cheese has always been pressed in cylindrical forms of varying sizes, but in
general rather large. When these large cheeses are cut they lose moisture,
so the cut surface dries rapidly. In addition, if the cheese is well ripened,
loss occurs through crumbling.
In packing cheese in cans, the cheese, after pressing, is cut into the desired
shape. Since hydrogen sulfide is often liberated during ripening of cheese,
it is preferable to wrap the cheese in parchment and it is necessary to use
a lacquered can, for the hydrogen sulfide tends to form a black product
with metals such as iron, copper, or lead.
Processed cheese. Rogers states that before the development of the
can in which Cheddar cheese may be ripened, the "only commercial method
for putting Cheddar cheese into a more attractive and convenient form is
the one known as processing. After the rind is removed, the cheese is
ground, a small quantity of water and an emulsifier, usually sodium citrate,
are added, and the mass is heated with constant stirring until it becomes
fluid. The emulsion is run into forms, which in many cases are boxes lined
with tinfoil, in which it is sold. The cheese hardens quickly and, as the
wrapping adheres closely, there is no trouble from molds. Moreover, as the
temperature is high enough to constitute pasteurization, most of the bacteria
are killed and the enzymes destroyed, so that ripening is stopped. In this
process, much of the original character of the cheese is lost; but, in spite
of this objection, the advantage of the package is so great that a large part,
possibly one-third, of all the cheese made in the United States is sold in
this form."
Templeton and Sommer have investigated various salts that may be used
as emulsifiers in processed cheese. They state the purpose of the salt is to
314 MILK AND CHEESE
prevent separation of the fat from the cheese and at the same time give the
finished product the desired body and texture. They quote Habicht as
stating that an alkaline monovalent cation combined with a polyvalent
anion, such as sodium citrate, is the ideal emulsifying salt. The physico-
chemical explanation is as follows: There is partial saponification between
the cation (sodium, if sodium citrate is used) and the fatty acids. The soaps
formed are good emulsifiers. In addition the anion, which is a solvent for
casein, combines with the casein of cheese so that a film of casein surrounds
each fat globule, thus emulsifying it and preventing its escape from the
mass. Later we find that the citrate ion is also a good peptizer of egg and
flour proteins.
Loaf cheese. Rogers states that blending is used extensively for
Cheddar and Swiss cheese. In this process the cheese is ground and heated
in steam-jacketed kettles, 60 to 70, and then poured into molds. In the
initial heating separation of the fat occurs; but with longer heating the
casein becomes plastic and stringy and encloses the fat. Further agitation
causes the mass to lose its plasticity and become the consistency of heavy
cream. At this time it is poured into the molds.
The plasticity of the cheese is an important part of the process. Once
the plasticity is broken it is almost impossible to restore it. The method of
manufacture, the degree of ripening, the acidity of the cheese, and possibly
other factors influence the degree of plasticity attainable in the heated
cheese and the length of time the mass will remain plastic. Sodium and
ammonia seem important in the emulsification of the product.
Cheese spreads. The term cheese spread may be applied to any pack-
aged form of cheese that can be easily spread \vith a knife at ordinary room
temperature. Templeton and Sommer name the types on the market as:
(1) cream cheese, mixed with pickles, olives, etc., (2) processed cheese of
such age and moisture content as to be "spready," and (3) processed cheese
with concentrated whey or skim milk powder added and of such fat and
moisture content that the mix will spread easily. They say that, since the
composition is quite different from cheese, as defined for Food and Drug
regulations, the product cannot be sold as cheese. Actually they are sold as
food products under proprietary trade names. The desirable spreading
qualities may be due to the moisture content or the fat content or both.
The use of cheese in cooked products. All of the factors that
affect the plasticity of the cheese when heated for blending, i.e., the degree
of ripening, the acidity, and method of manufacture, also affect its blending
properties with other ingredients in such dishes as rarebit, cheese souffle,
and macaroni and cheese. To these factors may be added the extent of
drying. For the cut or grated surface of cheese may dry rather extensively.
Hence, the protein in the surface area really needs soaking for hydration
before it will blend with other ingredients, or it may entirely lose its
plasticity.
Cream cheese may be combined with eggs, sugar, etc., for cheese cake or
REFERENCES 315
similar cooked dishes. But, in general, whether in its original state after
curing, or processed, the Cheddar type is the cheese usually combined with
cooked products.
The cheese is combined with white sauce or eggs at low temperatures and
by stirring. The temperature should be as low or lower than that used for
blending, 40 to 50C. often being preferable to 60 to 70C. As the
protein becomes plastic the fat exudes. Stirring aids in emulsifying this fat
with white sauce and casein of the cheese.
Cheese souffle. A colleague, Plagge, suggested a good method of com-
bining the ingredients for cheese souffle. The beaten egg yolks were added
to the white sauce before the grated cheese, because the addition of the egg
yolks cooled the mixture to a greater extent before the cheese was added.
However, another advantage of this order of mixing is that the egg yolk
aids in emulsifying the fat of the cheese. For the same reason beating with
a rotary egg beater as the cheese softens is a good method of blending the
cheese with the white sauce, since it more efficiently divides the cheese, thus
increasing the surface area for emulsification.
Processed cheese usually combines particularly well with white sauce
and egg yolk, because of its added water content and the emulsification
of the fat.
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Browne, C. A. A Contribution to the Chemistry of Butter-Fat. I. The Physi-
cal and Chemical Constants of Butter-Fat. J. Am. Chem. Soc. 21: 612 (1899).
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Burke, A. D., Woodson, F., and Heller, V. G. The Possible Toxicity of Butter-
milk Soured in Zinc Containers. J. Dairy Sci. 11: 79 (1929).
Chick, H., and Martin, C. J. On the "Heat Coagulation" of Proteins. IV. The
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Clayton, W. The Theory of Emulsions and Their Technical Treatment. J. & A.
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Influence the Component Fatty Acids of Butter. Biochemical J. 27: 889
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Doane, C. F., and Lawson, H. W. Varieties of Cheese; Descriptions and Anal-
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316 MILK AND CHEESE
Service and Regulatory Announcements. U. S. Dept. Agri. Revision 4,
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COOKING VEGETABLES IN MILK 317
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MILK
Cream of Tomato Soup
Experiment 55.
To determine the best method of combining ingredients in making cream
of tomato soup.
A. Use:
Milk y* cup 60 grams
Tomato juice ^4 cup 60 grams
Salt >js teaspoon
1. Combine by adding tomato juice to the milk. Why? Combine cold tomato
juice and cold milk, heat hot enough to serve, and 'add salt.
2. Repeat 1, but heat slowly in the top of a double boiler.
3. Combine hot tomato juice, hot milk, add salt.
4. Add the hot tomato juice to cold milk, heat, add salt.
5. Add the cold tomato juice to hot milk, heat, add salt.
6. If one curdles badly, repeat, but add first to the tomato juice 1/32
teaspoon of soda. If none curdle, prepare 6 by any method desired. What is
the effect of soda on the flavor? On curdling? Why may tomato juice cause
the milk to curdle? Why may curdling sometimes but not always occur by
some methods of mixing?
B. Use:
Milk y, cup 60 grams
Tomato juice y cup 60 grams
Flour y tablespoon 3.5 grams
Butter >2 tablespoon 7 grams
Salt Y% teaspoon
1. Make a sauce of the milk, flour, and butter; add cold tomato juice, and
heat.
2. Repeat 1, but add hot tomato juice to the sauce.
3. Make a sauce of the tomato juice, flour, and butter. Add to the cold
milk. Heat.
4. Repeat 3, but add the tomato sauce to* the hot milk. Does the addition
of flour lessen the tendency to curdle? Can cream of tomato soup be made
without the addition of soda?
Results.
Cooking Vegetables in Milk
Experiment 56.
To determine the effect of cooking vegetables in milk. Use green string
beans, asparagus, or carrots.
318
MILK AND CHEESE
1. To 24 cup of milk add ^ pound of string beans. Cook until tender.
The beans may be shredded in long strips to hasten cooking.
2. Repeat 1, but have the milk boiling before adding the vegetable.
3. Repeat 1, but add the vegetable to one-third of the boiling milk. Add
the remainder of the milk in small portions during cooking.
4. Repeat 1, but add 1/32 teaspoon of soda to the milk.
5. Repeat 1, but use cabbage or cauliflower.
Do any curdle? Is there any difference in the size of the curds formed
in cooking by the different methods? Why may one vegetable cause the milk to
curdle but another vegetable not cause curdling? If you wish to add milk for
seasoning to a vegetable like asparagus or green beans, how would you add it
to prevent curdling? Is it desirable to use soda?
Number
Curdle
Texture of milk
Comments
Results and conclusions.
Ham Baked in Milk
Experiment 57.
To bake ham in milk.
1. Use mild-cured ham in 1-inch slices. To /^ pound of the ham 1 inch thick
add 1 tablespoon of medium-brown sugar, sprinkling it evenly over the ham.
Add y 2 cup of milk and bake at 125C. (257F.) until tender. The size of
the dish should be such that the milk barely covers or just reaches the top
of the ham.
2. Repeat 1, but prewarm the milk by boiling it before adding to the ham.
3. Repeat 1, but add only one-third of the milk. After baking 30 minutes
add the remaining milk in small portions at intervals of a few minutes.
4. Repeat 1, but add 1/32 teaspoon of soda to the milk.
5. Repeat 1, but use evaporated milk. Dilute /4 CU P f evaporated milk with
J4 cup of water and add this diluted milk to the ham.
6. Repeat 1, but bake the ham at 175C. (347F.) until tender.
In which experiments does the milk curdle? Are some curdled worse than
others? What is the effect of a higher temperature upon curdling? Compare
the flavor of ham.
Number
Texture of milk
Texture of meat
Flavor
Comments
Results and conclusions.
The series may be repeated, omitting the sugar and using pork chops or fish
instead of the ham. There is less tendency to curdle with the fresh meat.
COTTAGE CHEESE 319
Junket
Experiment 58.
To determine the conditions most favorable for the clotting of milk by
rennin.
1. Use y-t, cup of raw milk warmed to 35 to 40C. Add % oi a junket
tablet that has been powdered and ^2 tablespoon of sugar. Stir to dissolve.
Put the junket mixture into a glass container or a Pyrex baking cup. Let
stand at room temperature. Keep a record of the time required for setting.
Determine when it is set by tipping the container slightly to one side.
2. Repeat 1, but use pasteurized milk.
3. Repeat 1, but set in the refrigerator after adding the junket.
4. Repeat 1, but dissolve the junket in 1 tablespoon of water. Boil, concen-
trating the water to 1 teaspoon. Add to the milk and sugar.
5. Repeat 1, but boil the milk, then cool to 35 to 40C. before adding
the junket.
6. Repeat 1, but dilute the milk with water, using % cup of water and
]/4 cup of milk.
7. Repeat 6, but use cereal water instead of water for diluting the milk.
The cereal water should be a little thinner than the consistency of a medium
white sauce.
8. Repeat 1, but add 1/16 teaspoon of soda to the milk.
9. Repeat 8, but increase the soda to l /4 teaspoon.
10. Repeat 1, but double the amount of sugar using 1 tablespoon (12.5
grams).
11. Add 1 tablespoon of grated raw pineapple juice to ]/2 cup of milk. Add
the sugar but not the junket.
Which ones set? Which do not set? Explain. Compare the firmness of the
clot formed in the various experiments.
Number
Clotted
Texture of clot
Flavor
Results and conclusions. -
Cottage Cheese
Experiment 59.
To make cottage cheese.
A. From sweet milk.
1. To 1 cup of sweet milk warmed to 35 to 40C. add ^2 of a powdered
junket tablet. Leave at room temperature until it has set. Pour into a cloth
sack and let drain for a few minutes. Determine the amount of cheese
obtained. Compare the texture and flavor of the cheese with that from
clabbered milk. What is the yield of cheese?
320
MILK AND CHEESE
B. From sour milk.
1. Sour milk that has formed a clot is called clabbered milk. Boil 1 cup
of clabbered milk 1 minute. Pour into a cloth sack and drain for a few
minutes. What is the yield of cheese obtained?
2. To 1 cup of clabbered milk add 1 cup of boiling water. Determine the
temperature. Drain through a cloth sack for a few minutes and determine the
yield of cheese obtained.
3. Heat 1 cup of clabbered milk in a double boiler until the whey separates
from the curd. Take the temperature. Follow directions under 1.
Compare the resulting cheese in texture, consistency, and flavor. What is
the effect of a high temperature upon curd of milk that has been precipitated
by souring? What temperature is preferable for heating clabbered milk to
make cottage cheese? Which method is preferable? Compare with the cottage
cheese made from sweet milk and junket.
Temperature to which milk
is heated
Yield
Texture
Flavor
Comments
Results and conclusions.
Cheese
Experiment 60.
To determine the effect of heat upon cheddar cheese.
A. The melting point.
1. Place some grated cheddar cheese in a test tube. To determine the melt-
ing point place a thermometer in the test tube. Melt the cheese by immersing
the test tube in water and heating the water. Compare the melting points
of several samples of cheddar cheese. Notice the consistency of each cheese,
its dryness, hardness, etc., before and after melting.
2. Repeat 1, but use the Kraft or other varieties of cheddar cheese that
have been put in sealed or other types of containers.
B. Effect of temperatures above the melting point.
1. After observing the consistency and texture of the cheese from Al and
A2, put the tubes in warm water and heat to temperatures above the melting
point. Notice all changes that occur.
C. Combining the cheese with milk.
1. Combine about 2 level tablespoons (14 grams) of grated cheese with Y
cup of milk (60 grams). Heat in the upper part of a double boiler. Note the
melting point of the cheese. Continue heating and describe the changes that
occur in the cheese-like mixture.
Does the dryness, texture, or fat content have any effect upon the melting
point? From the results obtained, what would you conclude about combining
cheese with other foods? Should cheese be heated directly over or under the
fire? If so heated, what temperature should be used? Should cheese be covered
CHEESE SOUFFLE
321
with sauce and bread crumbs in macaroni and cheese before putting in the
oven? Why?
Sample
of
cheese
Melting
point
Texture of
cheese before
melting
Effect of
melting and
heat
Comments
Results and conclusions.
Welsh Rarebit
Experiment 61.
To determine the most satisfactory method of combining ingredients for
Welsh rarebit.
1. Prepare a medium white sauce using:
Milk
Flour
Butter
tablespoon
tablespoon
122 grams
3.5 grams
7 grams
Remove from the fire and cool to 40C. Add % cup (28 grams) of grated
cheese to the sauce. Stir with spoon or beat with rotary egg beater until the
cheese is melted and blended with the sauce. Place in top of double boiler and
heat slowly to serving temperature.
2. Repeat 1, but add the cheese to the hot sauce.
3. Combine l /2 cup of milk and 1 egg (48 grams). Add l /l cup (28 grams)
of grated cheese and stir.
4. Repeat 3, but add the cheese to the milk. Heat in a double boiler until
the cheese melts. Add the beaten egg and cook until the mixture thickens.
Compare the results for consistency, flavor, smoothness, and ease of making.
Does the consistency of the cheese before its addition to the milk have any
influence upon the ease of blending with the milk? What types of cheese blend
most readily with the milk? If grated cheese that does not blend well with
the milk is soaked in the milk before heating, would this aid the ease of
blending?
Cheese Souffle
Experiment 62.
To determine a satisfactory method of combining and baking cheese souffle.
Recipe :
Butter
Flour
Milk
Egg yolks
Cheese, grated
Salt
Egg whites
3 tablespoons 42 grams
2 tablespoons 14 grams
T/ 122 grams
54 grams
cup
teaspoon
56 grams
90 grams
322 MILK AND CHEESE
Directions for mixing:
Melt the butter. Add the flour and salt and blend with the butter. Add the
milk and bring to boiling, stirring continuously. Remove from the stove and
beat the egg yolks thoroughly. Add egg yolks to the white sauce and blend.
Add the grated cheese and mix thoroughly, using a spoon or a rotary egg
beater. Fold in the stiffly beaten whites and pour in baking dish buttered on
bottom only.
A. The time of baking.
Prepare the whole or \ l / 2 times the recipe of whatever amount is necessary
for the size baking dishes used. After mixing, divide, putting equal portions
in three dishes. If possible set all three dishes in a large pan in the oven. Pour
boiling water around the dishes and bake. Oven temperature 175C. (347F.).
The time of baking may need to be varied, time given being suggestive, because
the time will vary with the quantity of water poured around the baking
dishes. The souffles should be baked until little or no shrinkage occurs on
removal from the oven.
1. Bake 40 minutes.
2. Bake 50 minutes.
3. Bake 60 minutes.
B. The temperature of baking.
Follow directions given under A. What modification of time will need to
be made ?
1. Bake one part at 160C. (320F.).
2. Bake a second part at 175C. (347F.).
3. Bake a third part at 190C. (374F.).
C. Compare baking the souffles in dish surrounded by hot water and with-
out water. Use temperatures and time found best under A and B. What modi-
fication of time will need to be made for those baked without water? Which
conducts heat more readily, water or air?
D. The method and temperature of combining ingredients.
Bake at temperature and time found best under A, B, and C.
1. Follow directions for mixing under A.
2. Reverse the order and temperatures for adding the cheese and egg yolk.
Add the cheese to the slightly cooled white sauce. Mix, then add the beaten
egg yolks.
3. Add both the egg yolks and cheese to the slightly cooled white sauce.
Mix.
Compare the volume, tendency to shrink, and texture of the souffles. What
temperature should the white sauce be when the cheese is added? Would this
vary with different kinds of cheese, that is loaf, processed, and cheddar? Would
it vary with degree of ripeness or dryness of the cheese? What is a desirable
method of making and baking cheese souffle?
CHAPTER X
EGG COOKERY
Structure and composition. The shell forms about 11 per cent of
the egg and is largely composed of calcium carbonate with some mag-
nesium carbonate, calcium and magnesium phosphates, and organic matter.
Century Photos, Inc.
FIG. 32. Showing standing up quality of yolk and white of a fresh and a
deteriorated egg.
Within the shell is the shell membrane, a thin, semi-permeable membrane
made up of two layers, the inner and outer. After the egg is laid, its con-
tents cool and shrink. The air cell at the large end of the egg is formed
during this shrinkage by separation of the two membranes.
For cookery purposes the white and yolk are the important parts of the
egg. The white is clear, transparent, and jelly-like. It composes about 57
per cent of the weight of the whole egg. The layer next the shell is a thin
323
324
EGG COOKERY
soft white, its relative proportion varying somewhat at time of laying.
Fig. 32. Next comes a layer of rather thick, viscous white, containing a
larger proportion of mucin than the thin white. Beyond this is a small
layer of thin white surrounding the yolk. Schaible, Moore, and Davidson
say that the thick, "firm white is of laminated structure, composed of
concentric layers containing mucin fibers." If a freshly laid egg is broken
Courtesy of Institute of American Poultry Industries and
P. J. Schaible, J. M. Moore, and J. A. Davidson, Michigan
FIG. 33. Showing the laminated structure of firm egg white, yolk removed.
into a large quantity of distilled water (the thick white having been slit
with scissors on one side to remove yolk) and allowed to stand, the mucin
and probably some globulin are precipitated at the edge of the cut surface.
Six or more sheets or layers, one over the other, can be distinctly seen.
Fig. 33.
The chalazae are dense cord-like strands of white substance, one on each
side of the yolk, which anchor the yolk near the center of the egg. They
allow the yolk to revolve. Being dense the chalazae are not broken down
readily when the egg is beaten, hence they are often caught on the blades
or wires of the egg beater.
COLOR OF SHELL AND YOLK
325
The yolk forms about 32 per cent of the whole egg. It is separated from
the white by a yolk sac, called the vitelline membrane. The yolk is made
up of layers. See Fig. 34. The fat is more concentrated around the germ
spot; hence its specific gravity is less and when the egg is turned the yolk
rotates so that the germ spot is always uppermost. In eggs of average size
the white usually averages about 30 grams and the yolk about 18 grams.
Composition. The composition of the white is approximately 86.2 per
cent water; 12.3 per cent protein; 0.2 per cent fat; and 0.6 per cent
Blastoderm
Shell Cuticle
-Shell
Chalaza "^^^^^^^ ! -*-^=^2^ Fluid Albumen
I Layers of White Yolk
Courtesy of Institute of American Poultry Industries.
FIG. 34. Diagram showing internal structure of an egg.
mineral. The composition of the yolk is about 49.5 per cent water; 33.3
per cent fats, including lecithin and cholesterol; 15.7 per cent proteins; and
1.0 per cent minerals.
Color of shell and yolk.- The color of the shell is determined by
inheritance, certain breeds laying white, others brown-colored shells. The
Barnaveldters lay eggs with nearly chocolate-brown shells.
The coloring matter of the yolk, according to Palmer, Mattikow, and
others is xanthophyll, with a small proportion of a carotene-like pigment.
The intensity of the yolk color is determined by the amount of xanthophyll
in the food of the hen. The color of the yolk may vary from a very pale,
almost white yolk, through deeper yellows to orange and finally a deep-
red-orange. Some feeds may produce red-colored yolks. Some attempts
have been made to work out color charts, giving each shade a number ; but
most of these are only tentative. It is an advantage for bakers and mayon-
naise manufacturers to obtain yolks of uniform color to insure uniformity
326 EGG COOKERY
of color of their products. A small number of manufacturers at present do
specify the color of the egg yolks when they place their contract for them.
Reaction of eggs. The egg white is alkaline. Sharp found that the
pH of the white varies from 7.6 to 9.7, whereas the yolk of fresh eggs
averages pH 6.0 or slightly low^er. The pH of both the white and yolk
increases with age because of the loss of carbon dioxide. Sharp and Powell
state that since the loss of some carbon dioxide cannot be prevented before
the pH is taken, that a pH of 7.6 is probably too high for freshly laid eggs.
With further loss of carbon dioxide the />H may increase to 9.5. Then,
probably owing to break down of some of the egg protein, the />H decreases.
The pH of the yolk may reach 6.8, but changes more gradually than that
of the white. When the whole egg is beaten so that the white and yolk are
mixed, a />H intermediate between that of the white and yolk is obtained.
Egg Quality
The term "quality" as applied to eggs refers ultimately to their desir-
ability for human consumption. When an egg deteriorates its cooking
qualities are altered. It is commonly accepted that an egg of high quality
is better for poaching, boiling, and frying than one of inferior quality. At
present, for trade use, eggs of quality are defined as those having a rela-
tively high percentage of thick to thin white, and a high percentage of yolk
solids. These eggs, when broken on a flat surface, do not tend to flatten
out as quickly nor to so great an extent as eggs of poorer quality. See
Fig. 32.
Tests for quality. A candler's grading of the egg is based largely on
the size of the air cell and the visibility of the yolk. Perry found that yolk
color, ascertained after breaking the egg, influences the yolk shadow and
the yolk movement, as determined in candling. The dark yolks cause a
darker shadow and increase the apparent movement, though the percentage
of thick albumen did not influence the yolk shadow and movement. The
air cell increases in size with loss of water from the egg. The less the
humidity of the air in which the egg is stored, the greater the loss of water.
When water is lost to the outside air the total solids of the egg increase.
The changes in the cooking quality of the white and yolk may not be so
detrimental as when the water loss is prevented. Since the size of the air
cell increases with the loss of water, the humidity of storage rooms is
usually controlled to prevent a large moisture loss. But other changes, more
detrimental to the quality of the egg than water loss, may occur.
Almquist, Givens, and Klose say that the transmission of light varies
for different layers of egg albumen, being lowest for the firmest or gelat-
inous layers. They find the transmission of light to be correlated with the
percentage of mucin in the albumen. In addition it varies w r ith the tem-
perature and />H, both of which affect the physical condition of the mucin.
FACTORS AFFECTING QUALITY OF EGGS 327
At lower temperatures and at lower pH the translucency of the mucin
fibers is lessened.
Wilcke used a torsion pendulum to measure externally the interior
viscosity of an egg and from observations worked out an index K, which
was a measure of the combined viscosity of the entire contents of the egg.
He found that the K value increased with increased weight of the eggs,
but that the rations used did not affect the K values of the eggs produced
by hens on the rations used in his study. The index, K, is a characteristic
of the individual hen.
Standing-up quality of the yolk. Sharp has worked out a system of
determining the quality of the egg from the standing-up ability of the
yolk. If a fresh egg of good quality is broken out of the shell, the yolk
stands up. But as the interior quality deteriorates the yolk flattens out
more and more readily until a stage is reached at which the yolk membrane
breaks, no matter how carefully handled, when the shell is broken. Both
the time the yolk is on the dish and its temperature affect the extent of
flattening, the flattening being greater with longer time and a higher
temperature. By dividing the height of the yolk by its width a numerical
index is obtained that indicates the quality of the egg. The measurements
of the yolk, after being freed of the white, taken 5 minutes after it is laid
on the Petri dish and at a temperature of 25C., give an average value of
about 0.41 for eggs 3 to 4 hours old. With deterioration of the egg the
index becomes less, and breaking occurs when the index falls to about 0.25.
The standing-up ability of the white may also be used to determine
egg quality.
Vitelline membrane strength. Another method for determining quality is
to measure the strength of the vitelline membrane. The average thickness
of this membrane has been reported to be about 64/100,000 of an inch. In
a fresh egg its bursting strength is about 0.065 pounds per square inch.
With deterioration the strength of the membrane decreases and the yolk
breaks easily when the strength has fallen to a little over half this value.
Factors affecting quality of eggs. Fresh-laid eggs vary in propor-
tions and viscosity of the thin and thick white. The yolk membrane also
varies in strength. These variations are probably due to feed, the season
of the year, the period of the laying cycle, and individual characteristics of
the hen. It has already been mentioned that Wilcke found that the rations
did not influence the viscosity of the egg in his investigations, but he states
his work does not rule out this factor. Lorenz and Almquist report that
the percentage of firm white is lowered by higher air temperature during
the hours immediately after the egg is laid, resulting in an apparent seasonal
variation in internal egg quality. The poorer quality of eggs obtained during
summer months is attributed to the higher temperature during this season.
The finest quality eggs are claimed to be those laid in the spring, which
coincides with the time of greatest production.
328 EGG COOKERY
Preservation and deterioration of eggs. Sharp states that "as soon
as the egg leaves the hen it begins to decline in interior quality and the best
we can hope to do is to retard these changes as much as possible. They
cannot be stopped, they can only be retarded. An egg a week old may have
deteriorated more in quality than an egg properly cared for which is a
year old."
Eggs are preserved by (1) storing at low temperatures, (2) by freezing,
(3) by drying, and (4) by oil dipping.
Storing at low temperatures. In commercial storage the temperature,
humidity, and air currents are controlled, the last to prevent mold growth.
A high moisture content in the storage air lessens the amount of the water
evaporated from the egg, but encourages mold growth. The storage tem-
perature is usually maintained at 29 to 30F. In addition chemical control
of the atmosphere is frequently practised in the storage rooms. Stewart and
Sharp state that at 30F., if 0.6 per cent carbon dioxide is used, the pH
of the egg white will be maintained at 8.0 to 8.1. If the concentration of
carbon dioxide is too high, the white becomes turbid, but loses this turbidity
after loss of some carbon dioxide from the egg on breaking.
Most of the eggs placed in low temperature storage are stored during
March, April, May, and June. More than half of the annual supply of
eggs is laid during these four months. Withdrawal of eggs from storage
usually begins in August, reaches its peak about November, and the supply
is generally exhausted by January.
Frozen eggs. The use of frozen eggs has increased very rapidly in the last
10 years. The eggs are broken out of the shell for freezing, which gives
an opportunity for increasing contamination with bacteria. If eggs are frozen
quickly after being broken, little bacterial growth takes place. Swenson
and James found that fewer organisms survived quick freezing than delayed
slow freezing. They also report that the addition of carbon dioxide to the
egg batter just prior to freezing was detrimental to survival of bacteria.
Eggs are frozen whole, the whites and yolks being mixed by beating. The
whites and yolks are also frozen separately. Freezing alters the physical
characteristics of the yolk, as it is more viscous after defrosting. Hence to
prevent its becoming so stiff and gummy that it does not mix readily with
other ingredients, before being frozen it is beaten and a small percentage
of salt, sugar, particularly dextrose, or some suitable edible ingredient is
often added. Some of these processes are patented, and the proportion of
ingredients added as well as the manner of incorporation are not generally
known.
Frozen whole eggs, egg yolks, and egg whites are usually prepared in
30-pound lots, though some 10-pound lots are frozen. A pound of frozen
whole eggs is equivalent to about 10 fresh eggs. As yet frozen eggs are
not on the retail market.
Drying. The use of dried eggs is decreasing in the United States, the
frozen eggs taking their place in many products.
FACTORS CAUSING DETERIORATION 329
Oil dipping. Oil dipping, shell treating, or processing of eggs is increas-
ing rapidly. This process consists of dipping the egg in some kind of oil to
seal the pores of the egg shell, thus retaining the carbon dioxide within
the egg.
Swenson, Slocum, and James report that a special white, odorless, taste-
less mineral oil of right viscosity and low enough pour-point (40F.) has
been developed to be applied to the shell at temperatures of 60 to 80F.
They also state that oiling shell eggs, especially by the vacuum-carbon
dioxide method, tends to maintain the pH of the egg white at 7.9 0.3,
which is below the optimum for proteolytic activity. Sharp and Wagenen
state that if eggs are oil dipped fairly soon after they are laid, the white
will have a pH value of 8.0 or less at the end of the storage period. If oil
dipping is to be of value in preserving the eggs they must be dipped before
too much carbon dioxide has escaped.
Factors causing deterioration. The causes for deterioration of eggs
may be listed as follows: (1) action of the enzyme trypsin, (2) alkaline
hydrolysis, and (3) chemical changes and changes due to bacterial action.
The changes brought about by these factors may be speeded up or retarded
by temperature and reaction.
Enzyme action. Balls and Swenson report that trypsin, a proteolytic
enzyme, is found only in the thick white. Its action, i.e., protein splitting,
which reduces the proportion of thick white in the egg, is speeded up by
increase in temperature, its greatest activity occurring near body tempera-
ture. Sharp has found that the weakening of the yolk membrane is greater
in 2 days at 98.6F. for eggs stored in air containing ordinary amounts of
carbon dioxide and at 80 per cent humidity than after 5 days of storage
at 77, or 20 days of storage at 60.8, or 100 days of storage at 35.6F.
Likewise a pH of about 9.25 may be reached in 2 days at 37C., in 5 days
at 16, and in 10 days at 2C. Or, in other words, carbon dioxide escapes
more slowly and enzyme action is also slower at lower temperatures. The
reaction of trypsin is also speeded up as the reaction becomes more alkaline,
the optimum activity according to Swenson, Slocum, and James occurring
at pH 8.4 to 8.8. Thus with loss of carbon dioxide from the egg, the action
of the trypsin is increased. Balls and Swenson found that the action of the
trypsin is decidedly speeded up by injecting enterokinase into the thick
white, which also gives proof that the enzyme is trypsin, since enterokinase
activates only trypsin. The thin white contains an anti-trypsin which inhibits
the action of the trypsin. Therefore, when the thick and thin white are
mixed together the action of the trypsin is inhibited. This mixing of the
thick and thin white before freezing may be one reason for the claim made
by many users of frozen eggs that frozen eggs are superior to and more
uniform in quality than fresh eggs. Balls and Swenson state the amount
of trypsin varies greatly in individual eggs of the same lot.
Alkaline hydrolysis. Alkaline hydrolysis of proteins, the breaking down
of the protein into smaller units, is also speeded up as the egg becomes more
330 EGG COOKERY
alkaline by loss of carbon dioxide and as the temperature increases. Alkaline
hydrolysis of protein occurs independently of enzyme action.
Chemical changes and changes due to bacterial action. Slow chemical
breakdown may cause off flavors and changes in eggs, but true rotting of
eggs is caused by microorganisms.
Eggs which are infected with a large number of molds and bacteria
ordinarily do not keep well. Microorganisms cannot always be detected in
eggs in the shell, yet the eggs deteriorate in storage. But, in general, eggs
with clean shells are comparatively free from bacteria. Reetger found that
not over 4 per cent, and usually a smaller number, of eggs with clean shells
were infected with bacteria. Egg shells vary in porosity and some eggs
have a few very large pores. Infection with bacteria is easier through these
large pores. Eggs having dirt on the shell are most easily infected. Bryant
and Sharp report that washing of such eggs is not the cause for deteriora-
tion, if they are handled properly after washing. The deterioration of
washed eggs is caused by bacterial infection of the egg from the dirt on
the shell.
Changes in eggs with deterioration. The most important changes
occurring in eggs during deterioration are : ( 1 ) the thick white becomes
less viscous and jelly-like, gradually changing to a thin watery white. (2)
Water passes from the white to the yolk increasing the size and fluid
content of the yolk, thus decreasing the yolk solids. In addition the yolk
membrane weakens and, if the weakening has progressed far enough, breaks
when the shell is opened. (3) Loss of moisture usually occurs. (4) The
egg may absorb foreign or off odors. (5) With continuous loss of carbon
dioxide the alkalinity of the egg increases.
Properties of Egg Proteins
The extensive use of eggs in cookery is made possible by their protein
content. The protein coagulates during heating, thus bringing about
thickening as in custards or the binding of pieces of food together as in
croquettes. The proteins of the egg are good emulsifying agents. The pro-
teins form elastic films when beaten, thus incorporating air, which is used
as leavening in such products as angel cakes and souffles. The elasticity of
the egg protein is also important in products such as popovers where the
egg stretches with expansion of steam, and later coagulates to aid in form-
ing the framework of the popover.
The proteins of the egg. The proteins of the white are ovoalbumin,
ovoglobulin, and ovomucin. There may be small amounts of other proteins
and it is also possible that each protein is made up of component fractions.
Hughes and Scott give the relative proportions of the proteins in the three
portions of the white as shown in Table 41.
The principal protein of the yolk is ovovitellin. Sell, Olsen, and Kremers
ISOELECTRIC POINT OF EGG PROTEINS
331
TABLE 41
PERCENTAGE OF THE TOTAL NITROGEN CONTRIBUTED BY EACH OF THE THREE
PROTEIN FRACTIONS (Hughes and Scott)
Outer thin layer
of egg white
Thick layer
of white
Inner layer of
thin white
Ovomucin
1.91
5.11
1.10
Ovoglobulin
3 66
5.59
9.89
Ovoalbumin
94 43
89 18
89.29
separated salted egg yolk into a soluble lipoid fraction and an insoluble
residue. The latter consisted of sodium chloride and the protein-like mate-
rial of the yolk. This residue they called lecitho-protein. It composed about
32.5 per cent of the yolk. This protein fraction contained nearly one-half
the total lecithin of the yolk.
Solubility of the proteins. The albumin of egg forms a sol with
water and dilute salt solutions. The globulin forms a sol in dilute salt solu-
tions, but not in pure water. The globulin composes about 6.5 per cent of
the total proteins of the egg.
Egg-white proteins belong to the group of hydrophilic colloids. Egg
white and water are mutually soluble. Usually the addition of 1 table-
spoon of water to an egg white, unless it is very watery, increases its ex-
tensibility, and when the egg white is whipped a larger volume is obtained.
But with increasing quantities of water a stage is reached at which the
egg white loses too much of its rigidity and will no longer retain air in
small bubbles, the bubbles being large and floating on the more liquid
part.
The ovovitellin of the egg yolk is combined with phosphorus and be-
longs to the phosphoprotein group. It is insoluble in water but is soluble
in dilute salt solutions and in dilute alkalies.
Isoelectric point of egg proteins. Loeb has reported the isoelectric
point of egg albumin as pH 4.8. Some investigators give />H 4.7 as the
isoelectric point. Above the isoelectric point the albumin combines with
bases to form salts like sodium albuminate; below the isoelectric point it
combines with acids to form salts like albumin acetate, citrate, or tartrate.
Above the isoelectric point the protein is negatively charged; below, it is
positively charged. Since the reaction of the egg white is about pH 7.6 to
9, there will probably be few combinations of egg white with alkalies or
alkaline salts in food preparation that will increase its alkalinity. Many
combinations are made that increase its acidity. For example, the addition
of a teaspoon of cream of tartar, a salt with an acid reaction, to a cup of
332 EGG COOKERY
egg whites, proportions often used in angel food cakes, increases the acidity
and lowers the pH, often to about 7.5 or 7.0. As the proportion of cream
of tartar is increased, the />H is lowered to a greater extent. The addition
of fruit juices and fruit pulp to egg whites to make fruit whip, souffles, or
similar desserts, increases the acidity. When 1 to 2 teaspoons of lemon juice
are added to an egg white the pH is lower than 4.8.
No record could be found in the literature of the isoelectric point of
ovovitellin. When lemon juice is added to egg yolk, the mixture is thickest
at a pH between 4 and 5, as if the greatest tendency to curdle is at this
point. This might indicate that the isoelectric point of the egg yolk proteins
is between />H 4 and 5. This greatest thickening occurs with about 5 cc. of
lemon juice to an egg yolk.
The addition of an acid like vinegar or fruit juice to the white and yolk
beaten together tends to curdle the mixture. This occurs when the acidity
is in the vicinity of the isoelectric point. When sufficient acid is added to
lower the />H below the isolectric point of the egg proteins, and if the salt
formed, such as protein citrate, is soluble, the coagulum dissolves and the
mixture becomes smooth. With the exception of salad dressings and a few
sauces, there are probably not many instances in which enough acid is
added to lower the />H of the food mixture below the isoelectric point of
the egg protein.
Peptization of egg proteins. Peptization of egg proteins increases
the tenderness of some products. Freundlich states that peptization of pro-
teins is frequently brought about by low concentrations of electrolytes,
though to accomplish this the electrolyte must be intimately mixed with
the substance to be peptized. The hydroxyl, citrate, acetate, and tar-
trate ions are effective for peptizing egg proteins. For example, when
tomato or lemon juice is added to egg in amounts to bring the />H of the
egg slightly above or about the isoelectric point of egg albumin, the tender-
ness of omelets is definitely increased. In some instances peptization of the
egg proteins is detrimental. An example of this is the thinning of salad
dressings, thickened with only egg yolk, when heated above the temperature
at which optimum coagulation occurs.
Sugars (sucrose, dextrose, and levulose) through peptization tend to
prevent coagulation of egg protein.
Denaturation. Denaturation, by which soluble proteins are rendered
insoluble, of egg proteins is brought about in a variety of ways, including
the action of acids, salts, heat, mechanical agitation, and radiation. Mechan-
ical agitation or beating of egg white, as well as the tendency of proteins
in surfaces to form films, causes partial denaturation of the egg proteins.
Sugar tends to prevent this denaturation.
The theories for heat coagulation have been considered in Chapter I.
But, however the process of coagulation is brought about, the coagulation
temperature, the time required for coagulation, and the factors that cause
HEAT COAGULATION OF EGG PROTEINS 333
variation in coagulation temperature are of interest in egg cookery, because
they determine the temperature to which certain dishes, such as custards
and cooked salad dressings, may be heated. If heated beyond this point,
separation into solid and liquid may result and curdling occurs, or the salad
dressing may become thinner.
Coagulation temperature of egg white. Undiluted egg white coagu-
lates at about 60C. or becomes jelly-like at this temperature. Coagulation
may start at a slightly lower temperature, but the amount coagulated at
the lower temperature depends on how long the egg is held at that point.
In coagulating, the egg white changes from a clear, transparent mass to a
white and opaque one. If the egg white is heated slowly, a point is reached
about 62C. at which it will not flow in a test tube. It is still firmer
at 64 to 65 C. In cooking, the temperature is seldom held a long time
at a definite degree but may rise gradually and often rapidly.
Coagulation temperature of the egg yolk. The egg yolk requires a
higher temperature for coagulation than the egg white. It begins to thicken
at about 65 C. but does not reach a stage at which it does not flow until
about 70. Since the yolk does not change color during coagulation it is
more difficult to determine when it is coagulated.
When the white and yolk are mixed by beating and are heated slowly
the mass begins to thicken at 65 C. and becomes stiffer not far from 70.
Factors affecting heat coagulation of egg proteins. The follow-
ing factors affect the coagulation temperature of the egg proteins : ( 1 )
temperature, (2) time, (3) concentration of protein, (4) salt content and
its concentration, (5) reaction of the egg solution or mixture, and (6)
sugar.
Temperature and time. The rate of coagulation increases with increas-
ing temperature. At high temperatures it is so rapid that it seems nearly
instantaneous. Eggs cooked in boiling water will cook at a much faster
rate or in a shorter time than those cooked in water at 70 C. Chick and
Martin have found that "heat coagulation is a reaction with a high tem-
perature coefficient, the reaction velocity of which varies considerably with
different proteins and according to the acidity and saline content of the
solution." They have reported that the temperature coefficient for crystal-
line egg albumin in water solution and 1 per cent concentration is 1.9
times for 1C. rise in temperature. The temperature coefficient is greater
than 2 for the results of Lepeschkin given below. In cooking eggs or foods
containing large proportions of egg, the amount of coagulum formed at
a definite temperature depends upon the length of time the food is held at
the specified temperature and the number of degrees the specified tempera-
ture is above the point at which coagulation may begin. Using filtered egg
white, Lepeschkin found that, with water at a definite temperature, a
longer time was required before the egg appeared turbid at lower tempera-
tures than at higher temperatures. His findings may be summarized :
334 EGG COOKERY
C. Seconds required for coagulation
57.04 22,600
58.01 9,520
59.03 1,535
60 . 03 595
61.02 230
62.01 97
63.01 40
As the temperature of milk custards is elevated the firmness of the
custard is increased. At a definite temperature, depending on the rate of
heating, an optimum consistency is obtained. Heating to a temperature
higher than this increases syneresis and porosity of the custard.
Woodruff and Meyer found that by increasing the temperature from
79 to 91 by 4 intervals the strength, when tested by a gel tester of
distilled-water-egg custard gels with 0.2 M and 0.05 M sodium chloride
and 0.2 M magnesium chloride plus 23 per cent sugar, was increased. But
at the higher temperatures the gels were porous and undesirable. The con-
centration of egg used was approximately 2 to a cup of liquid.
Concentration. Robertson states, "The concentration of the protein, and
especially the presence of other substances in the solution, very markedly
affects the coagulation temperature." This is illustrated in egg cookery.
The whole egg coagulates at a temperature not far from 70 C. When 1
to 2 tablespoons of milk or water are added, as in the making of plain
omelets, coagulation occurs at a temperature above 70C. When 1 egg is
added to a cup of milk the coagulation temperature is much higher than
that of egg alone. It is about 80C., the amount coagulated at a definite
temperature depending upon the rate of heating. If 2 eggs are added to a
cup of milk the concentration of egg is greater than when 1 is used, and
coagulation under the same conditions for heating occurs at a slightly lower
temperature.
Salts. The salt content of the egg or of the material with which the egg
is combined affects the coagulation of the egg proteins. Lepeschkin has
shown that, if egg albumin is dialyzed so that the mineral content is low-
ered, the albumin does not coagulate on heating. He has also shown that
coagulation varies with the salt concentration, that some concentrations
cause coagulation and others do not. However, if, to the heated egg al-
bumin that has been dialyzed, salts are added, coagulation takes place,
but this often requires a definite concentration for maximum coagulation,
higher or lower concentrations not being so effective or failing to bring
about coagulation.
The effect of the salt content on coagulation can be shown by com-
bining egg as for custard, but substituting distilled water for the milk,
which when heated to 83 to 86C. does not gel. If to this distilled-water
custard a definite concentration of a salt is added, coagulation will occur
on heating. Salts which will bring about coagulation are iron lactate, ferric
pH AND COAGULATION OF CUSTARD 335
chloride, calcium chloride, sodium chloride, aluminum chloride, aluminum
sulfate, sodium sulfate, magnesium sulfate, sodium acetate, potassium
tartrate, sodium potassium tartrate, calcium phosphate (monobasic and
secondary), sodium and potassium phosphate. However, some produce a
firmer coagulum than others, for with each salt a definite concentration
brings about optimum coagulation. If the distilled-water custard is heated
to 83-86 before the salt is added, and the salt is then added, coagulation
occurs; but when the mixture is stirred, curdling occurs to a greater or
lesser extent. A milk-salt mixture, such as the Sherman or Steenbock formu-
las used in animal-feeding experiments, in the right concentration forms a
coagulum in distilled-water custards that is similar in consistency to that
produced by milk custards.
Concentration and valence of added salts. If the effect of electrolytes
upon hydrophobic and hydrophilic colloids is referred to in Chapter I, the
statement is found that the precipitation of the protein is brought about
by the ion having the opposite charge from that of the protein. In general,
the coagulating power of the ion increases with increasing valence, but
there are some exceptions to this rule, some monovalent ions being more ef-
fective than some polyvalent ions. In many cases there is a zone of maximum
coagulating effect. The effect of the concentration of the salt upon the
coagulation of the egg can be shown in the following way. If less than 1/16
teaspoon of ferric or aluminum chloride is added to an egg, a cup of distilled
water and 2 tablespoons of sugar, the custard coagulates on heating to 84C.,
though the coagulum is not so firm as when milk is used. However, if a
larger quantity of ferric or aluminum chloride is added to the mixture,
about Y^ teaspoon or more, the custard does not coagulate when heated to
84C. The reaction of the custard mixture with the small amount of
aluminum or ferric chloride given above is slightly acid to litmus, and
the larger quantities are decidedly acid to litmus. Hence, the larger quantity
of ferric chloride must peptize the egg proteins.
Woodruff and Meyer found that sodium chloride, sodium sulfate, and
calcium chloride, when used in 0.2 M concentration, produced gels of
approximately equal strength and slightly weaker gels than milk. Mag-
nesium chloride and sodium thiocyanate produced stronger gels than milk.
They concluded that the difference in strength of gels formed by various
electrolytes seemed to be a specific function of the cation and anion of
the salt, and independent of the pH of the solution. Increasing the concentra-
tion of each salt gave gels of greater strength until a maximum strength was
reached, after which further increases of the salt reduced the gel strength.
The relation of reaction to setting of custards. If hydrochloric acid is
added to the egg-distilled-water custard, so that the reaction is adjusted to
a /H above the isoelectric point of egg albumin, pH 4.8, coagulation occurs
within the range of pH 5 to 6. The coagulum is soft and not quite so firm
336 EGG COOKERY
as when salts are added, but it shows that a definite acidity tends to aid
coagulation.
The coagulation of egg-distilled-water custard with added salt is some-
what similar to the jellying of fruit jells in that it occurs at a definite
range of />H.
Coagulation occurs over a wider range of />H when milk is used with
the egg than when distilled water is used. If the pH is adjusted with
hydrochloric acid and sodium hydroxide, it occurs from pH 0.2 to 8.6 or
over even wider ranges. The reaction of a milk-egg custard mixture, with
no added acid or alkali, is between />H 6 to 7 with an average of about
6.5. This custard mixture was made up in a large quantity, and divided
into different portions. To these portions hydrochloric acid or sodium hy-
droxide was added to adjust the custard to the desired />H. As the />H
was lowered the firmness of the custard increased, until at about />H 5
curdling occurred. All custards with a />H below 5 curdled, the curd be-
coming very fine in texture, and forming a dense layer in the bottom of
the container. This layer decreased in amount as the />H was lowered
below the isoelectric point of egg albumin. At a />H 0.2 the custard was
badly charred, and the curd was very slight and fine, the custard quite soft.
With increased alkalinity above />H 6.5 the coagulum was less firm. The
custards could be placed in the order of acidity by the depth of color : the
greater the acidity the lighter the color, the greater the alkalinity the
deeper the color. The color ranged from light cream, through yellow, to a
deep orange-yellow.
Acids. Chick and Martin state that acid solution hastens the second
part of the heat-coagulation process, that is, the clotting or coagulation,
but does not hasten the first part of the process, the denaturation. They
have reported that acid accelerates the rate of coagulation. They state
that the influence of acid in accelerating the coagulation rate of a neutral
solution is at first relatively small, but with each successive addition of acid
its influence becomes disproportionately greater. Loeb using isoelectric crys-
talline egg albumin in a 1 per cent solution at a />H 4.8 found that it
coagulated at a temperature not far from 60C. When acid was added
and the />H lowered to 4.39 the coagulation did not occur until about
80C. With pH 4.25 coagulation did not occur at 95C.
Fruits that do not have a high acidity such as dates and figs may be
used in custards and tend to give a firmer custard, because they lower the
/>H slightly. More acid fruits, such as lemon juice, cannot be used in
very large quantities. The addition of quite acid fruit juices tends not only
to coagulate the casein and albumin but also to hasten curdling. Custards
that are made of milk that is slightly sour will curdle more readily during
heating. If the acidity has not reached the stage at which curdling occurs,
the custard is firmer.
Alkalies. Chick and Martin have found that in alkaline solution the
second part of the coagulation process, the aggregation or coagulation of
CUSTARDS 337
the protein, does not occur. If after heating the alkali is neutralized with
acid, coagulation occurs. Thus, if enough of an alkali or of an alkaline
salt is added to a custard to render the solution sufficiently alkaline, the
custard will not coagulate on heating. But if acidified after heating the
custard will "set."
Sugar. The addition of the non-electrolyte sugar to an egg mixture ele-
vates both the setting and curdling temperatures. In large enough quantities
it tends to prevent both coagulation and curdling. Its effect in preventing
coagulation appears to be proportional to the amount added, the greater
the amount added the greater the difficulty in bringing about coagulation.
Bancroft and Rutzler state that a "15-per cent egg white sol was not
prevented from coagulating by the addition of 0.25 gram of dextrose to
10 cc. of the sol. However, when the sol was saturated with respect to
dextrose heating in boiling water caused no coagulation."
Woodruff and Meyer found that 10 per cent of sucrose reduced the gel
strength of egg-milk custards heated to 83 C., approximately one-half. Add-
ing 30 per cent of sugar practically prevented coagulation. Adding sugar
also increased the translucency of the custard.
In the salad-dressing recipe given in Experiment 65, increasing the sugar
from J^ to 11 tablespoons (140 grams, about 30 per cent) elevates the
temperature for optimum thickness about 4 to 6C. Here in spite of the
fact that the acid tends to lower the coagulation temperature the effect of
the large quantity of sugar is still greater and the mixture must be cooked
to a higher temperature for optimum thickening.
Coagulation by other means. Flosdorf and Chambers found that audible
sound, frequencies (1000-15,000), coagulated solutions of egg albumin and
synthetic plasterin almost instantly at 30 C.
Jellinek placed a raw egg between two condenser plates connected to a
short-wave radio transmitter. After power of 1000 watts had been applied
for 5 minutes, the egg yolk was coagulated and hard, as if it had been
cooked, but the white was scarcely affected. The temperature of the yolk
at the end of this period was 140F., that of the white was 176F.
The Applications of Factors Affecting Heat Coagulation
to Preparation of Food Products
Custards. As can be deduced from the foregoing discussion, custards
containing a high proportion of sugar may not thicken satisfactorily for
serving purposes. A small amount of salt aids setting but too much in-
creases the tendency to curdle.
Pie fillings. One question often asked is why butterscotch fillings for
pies which are of a consistency for serving sometimes become thin and runny
after standing for a short time. This of course is different from the instances
in which thickening does not occur. There may be various factors that bring
about this result, but the effect of the sugar in elevating the temperature
338 EGG COOKERY
at which egg coagulates is one explanation. The proportion of sugar in
butterscotch fillings in different recipes varies from about 15 to 25 per
cent, or 15 to 25 grams per 100 grams of filling. A usual procedure is to
cook the sugar, cornstarch or flour, and scalded milk until thick. This
mixture is often added to the beaten yolks by stirring the hot mixture
into the yolks. Sometimes it is considered that the hot milk mixture will
coagulate or cook the egg yolk sufficiently. However, if the temperature
drops below 80C. during this procedure and the mixture is not reheated
the egg yolks will not be cooked sufficiently. The filling appears thick at
the time, but on standing it becomes runny. If sugar is added to uncooked
egg yolks, mixed, and left to stand for a few minutes the mixture appears
thinner and more runny. If the yolks are not cooked sufficiently they act
in much the same way, the sugar dissolving in the uncooked yolk and the
filling becoming runny. This has never been observed by the author if
the mixture is heated to a sufficiently high temperature after the egg yolks
are added. The same thing may occur in chocolate and lemon pie fillings,
although this in some instances is due to not using enough starch, the action
of the acid on the smaller amount of starch lessening the stiffness of the
filling. Another possible cause is the tannin of the brown sugar, because
the tannin has a dehydrating effect on many sols. But to date it has not
been possible to obtain thinning in the butterscotch filling by adding slightly
more tannin than might be found in the sugar.
Baked products. The addition of sugar to egg in baked products also
tends to delay coagulation or peptize the egg proteins and will be discussed
further under angel cake and cakes containing fats.
Cooked Salad Dressings
Vinegar, lemon juice, or a mixture of the two, is used in cooked salad
dressings. The two acids do not behave alike, particularly in regard to
curdling. The lemon juice contains citric acid and salts. Vinegar contains
acetic acid, and cider vinegar contains salts. If mustard, sugar, and salt
are kept constant in the recipe given in Experiment 65 with 72 grams of
egg yolk and a total of a cup of liquid, results similar to the following
may be obtained, provided the rate of heating is the same in each case. The
mixture is cooked in the upper part of a double boiler, 12 to 15 minutes
being required for the cooking process.
^>H Coats spoon
Water about C.
Vinegar }/% cup J^ cup 4.2 82 to 85
Vinegar Y, cup ^ cup 3.9 78 to 80
Vinegar Y- cup l /2 cup 3.6 76 to 78
Lemon juice }/% cup ^8 cup 3.6 82 to 85
Lemon juice % cup % cup 3.3 78 to 80
Lemon juice y cup Y* cup 76 to 78
COOKED SALAD DRESSINGS 339
One-fourth cup of either the vinegar or lemon juice gives a stiff er or
thicker dressing than l /% cup; ^ cup of vinegar or lemon juice gives a
thicker dressing than ^4 CU P- These results seem to agree with those of
Chick and Martin that acid aids coagulation. Increasing the quantity of
acid lowers the temperature at which the consistency for serving is reached.
The optimum dressing for serving is obtained at a temperature slightly
higher than the temperature for "coating the spoon." The salad dressings
become thinner after heating above this optimum temperature for serving;
the ones with lemon juice are thinner than those with the vinegar. An-
other peculiarity is that if a portion of these salad dressings is cooked to
as high a temperature as 92C., all those made with vinegar may or may
not curdle. The ones with lemon juice may not curdle, or those with the
smaller quantity of lemon juice may curdle at about 85C., but when
heated to a higher temperature the curds may partially or entirely dis-
appear. In all these instances the reaction of the dressings is probably below
the isoelectric point of ovovitellin. If heated only to the temperature at
which the dressings are thickest, the thinning is not noticeable if the dressing
is stored.
If 92 grams of whole egg are substituted for the egg yolk, the />H re-
mains practically the same, but the dressing when cooked contains fine
curds, those in the dressings made with lemon juice being finer than those
in the ones made with vinegar. Increasing the proportion of salt produces
a thicker product at a slightly lower temperature but one which curdles
at a lower temperature. Increasing the sugar in the recipe slightly elevates
the temperature at which the best texture for serving is obtained.
The explanation for the salad dressing's becoming thin and nearly its
original consistency when heated above the temperature at which the opti-
mum thickening occurs is that the acid and continued application of heat
bring about peptization of the protein. It is probably an illustration of a
partial or complete reversibility of heat coagulation and one of the most
common occurring in food preparation. It is probably the reason that usually
only one or no recipe for boiled salad dressing containing only egg yolk
as the thickening ingredient is given in most cook books. Too many cooks
have had the salad dressing return to its original consistency.
Salad dressing containing starch. If maximum thickening of both starch
and egg is desired when these two ingredients are used together in a boiled
salad dressing, the starch and all, or a part, of the liquid should be heated
to 95 C. or boiling before the egg is added. The maximum thickening of
cornstarch does not occur below 91 and of wheat starch below 95C.
Since the maximum thickening of the egg in the presence of vinegar or
lemon juice occurs at temperatures of 76 to 85 C. and thinning occurs at
higher temperature, this suggests that the thickened starch paste should
be added to the cold beaten egg and then heated to a temperature that
gives maximum thickening of the egg.
On the other hand, there is the possibility that part of the egg protein
340 EGG COOKERY
may not coagulate in the presence of starch, hence not thicken the salad
dressing. Bancroft and Rutzler, quoting Berlinsson, state that "albumin
is prevented from coagulating even in boiling water by the presence of
starch." However, this appears contrary to observed results in food prepara-
tion. Possibly there needs to be a certain concentration of starch before
coagulation is prevented or peptization of the egg protein may occur when
heated above the temperature for coagulation of the egg protein. It will,
at least, be an interesting point to investigate.
Eggs Cooked in the Shell
Effect of coagulation at low and high temperatures. Eggs cooked
in water held at 70 C. are not firm like those that are cooked in boiling
water. The white cooked at 70C. is very soft and jelly-like in consist-
ency. The yolk held at this temperature for an hour or longer has the
appearance of an uncooked yolk, but is more viscous, more waxy, thicker,
and does not flow like the uncooked yolk. The color also remains more
like that of the uncooked yolk, a deeper orange, instead of the yellow
which is developed in eggs cooked at higher temperatures. The white of an
egg cooked at least 12 minutes in boiling water is rather firm and may be
tough. Eggs cooked at temperatures between 70 and 100C. have tex-
tures intermediate between the ones described above, i.e., they are firmer
than the former and usually more tender than the latter.
By cooking for a short time at a higher temperature the outer edge of
the white may be firm to a depth depending on time of cooking, a portion
near the yolk may be unchanged, and the yolk may be unchanged or the
outer portion may be slightly cooked.
The softer coagulum at the lower cooking temperature has been ex-
plained as due to the effect of low temperature. Robertson suggests that it
may be due to only partial coagulation of the protein at the low tem-
perature.
The white of some eggs is often more tender than that of other eggs
cooked in the same lot. Perhaps this may be explained by the reaction, those
which are more alkaline coagulating less readily. There is also the possibil-
ity that the white of eggs cooked an extremely long time may become more
tender.
Barmore mixed egg white thoroughly and placed it in a cement briquette
mold. The mold was immersed in water of the desired temperature and left
40 minutes. The tensile strength and the depth a steel ball and rod would
penetrate were determined. Below 77.5C. the samples were too tender
to handle. The three tests all indicated a decided increase in tenderness as
the temperature of coagulation was reduced with the exception of the steel
ball at 93 and 101C. Here the data indicated that the change may have
decreased instead of increasing the toughness. The other tests gave opposite
results at these temperatures.
POACHED EGGS 341
Rate of heat penetration. The higher the temperature of the cooking
water, the more rapid is the rate of heat penetration. As the temperature
of the egg and water become more nearly equal the rate of heat trans-
ference is very much slower, but the temperature at the center of the yolk
even after cooking in boiling water for 4 hours or longer is never quite
as high as that of the water, but is a fraction of a degree lower.
Time required for cooking eggs in water. Since coagulation takes
place at a definite rate, which increases with a rise in temperature, both
the length of time the egg is left in the water and the temperature of the
water affect the coagulation rate, and thus the time necessary for cooking.
At a temperature just a little above the temperature at which coagulation
of the white occurs, 60 to 65C., a very long time is required to coagulate
the mass of the egg white. If the cooking temperature is 70 or a little
higher, more than an hour is required to coagulate the white and yolk.
At a cooking temperature of 85 to 90C. from 25 to 35 minutes are
necessary to have the yolk the same consistency throughout. A shorter time
leaves a portion of the egg yolk an orange color, instead of the uniform,
powdery yellow. At the temperature of boiling water about 12 minutes
are required to complete the cooking of the yolk uniformly. With increase
in height above sea level these times are lengthened.
The exact time of cooking at any given temperature depends upon the
temperature of the egg when placed in the water, the quantity of water
in relation to the size of the egg, and the rate of heating the water.
Poached Eggs
Fresh eggs are usually considered better for poaching than eggs in which
the physical quality has deteriorated, i.e., eggs with watery whites. Class
results substantiate this popular opinion, for eggs with thick viscous whites
can be poached satisfactorily with far less care than those with thin whites.
In poaching eggs it is desirable to have the temperature of the water near
the boiling point when the egg is added. Thus the outer portion of the
egg is coagulated in a short period of time. If desired, the cooking can
be completed at a lower temperature.
Since both the white and yolk tend to flatten on standing after being
broken out of the shell, poached eggs of better appearance are usually
obtained if the egg is broken just before it is added to the poaching water.
St. John and Flor have reported that the thin portion of the white coagu-
lates as satisfactorily as the thick portion if Y^ teaspoon of salt to a pint of
boiling water is used. The salt aids in coagulation. Eggs with about the
same proportion of thick and thin parts of the white are firmer when poached
in salted than in unsalted water. But for what food teachers call standard
products, eggs poached in unsalted water often have "a better appearance
than those poached in salted water. The ones cooked in salted water are
usually not so shiny. Occasionally the reverse is true. The added salt aids
342 EGG COOKERY
in coagulation, so that the thin portion of the white is less readily detached
from the thicker portion. But the appearance of the thin portion after
cooking in the salted water is often more puckered, wrinkled, and ruffled,
or is in voluminous folds around the thicker coagulated part. This detracts
from the appearance. Either a very hard water or a softened water is used
for poaching eggs in class work. It is possible that the natural salt content
of the water may effect coagulation, so that thin watery whites cooked in
Ames's water do not give as good appearing products as those obtained by
St. John and Flor.
The Formation of Ferrous Sulfide in Cooked Eggs
AVhen an egg has been cooked in hot water for 15 minutes or longer a
dark greenish color may be formed on the surface of the egg yolk. If the
egg is immersed in cold water immediately after cooking, the green color
is not produced or is less apparent than when the egg is left in the hot
w r ater to cool slowly.
The yolk contains most of the iron of the egg, about 85 times as much
as the white. According to Sherman, the sulfur content of the white is
slightly higher than that of the yolk, the white containing 0.214 per cent
and the yolk 0.208 per cent. The sulfur of the white is more labile and
more easily split off by heat than the sulfur of the yolk. Marlow and King
say that the sulfur in egg whites and yolk is organically bound and that
nearly all of it can be accounted for by the cystine and methionine sulfur.
Tinkler and Soar have shown that the green color is due to the forma-
tion of ferrous sulfide at the surface of the yolk. The white with prolonged
heating at high temperatures evolves considerable quantities of hydrogen
sulfide. The hydrogen sulfide combines with the iron of the yolk to form
ferrous sulfide which produces the green color. The amount of hydrogen
sulfide evolved depends on ( 1 ) the time of heating, (2) the temperature
reached, and (3) the reaction of the egg. In a short cooking period little
hydrogen sulfide is evolved. Likewise at a lower temperature a smaller
amount of hydrogen sulfide is formed. Tinkler and Soar have also shown
that the formation of ferrous sulfide takes place very, very slowly until
the yolk reaches a temperature of 70C. It is very seldom formed in eggs
cooked for 1 to \]/\ hours at 70C., or in eggs cooked 30 to 35 minutes
at 85C. Thus both the temperature attained by all or a portion of the egg
white as well as the time held at this temperature influence the amount
of hydrogen sulfide formed. In addition, as the reaction becomes more
alkaline, the sulfur is split off more readily. Therefore, the extent of
deterioration of the egg also affects the amount of hydrogen sulfide formed.
This explains why some eggs have more ferrous sulfide formed than other
eggs when cooked at the same time and cooled in the same manner. Tinkler
and Soar have reported that the uncooked yolk is acid in reaction but upon
being heated above 70 becomes alkaline.
BAKED AND SOFT CUSTARDS 343
Effect of rapid cooling upon formation of ferrous sulfide in
cooked eggs. Hydrogen sulfide is a gas. When the egg is placed in cold
water immediately after cooking the lowering of the temperature at the
surface of the egg lowers the pressure there. One of the things learned in
connection with the gas laws is that the pressure increases with increasing
temperature. Since the white near the shell reaches a certain temperature
more rapidly than the white near the yolk, more hydrogen sulfide is split
off near the shell. But, since the temperature near the yolk is lower, hence
has less pressure than near the shell, the hydrogen sulfide diffuses through
the white towards the yolk. However, if the egg is placed immediately in
cold water after cooking, the hydrogen sulfide diffuses to the surface of
the egg, owing to the reduced pressure, but if left in hot water, or to cool
in the air, the gas does not diffuse so quickly to the surface and ferrous
sulfide is formed at the junction of the egg white and yolk. Tinkler and
Soar have found that eggs cooked 15 minutes in boiling water and cooled
slowly have some green color at the surface of the yolk; if cooled quickly,
none or very little green color develops. Cooking in boiling water for 30
minutes gives a great deal of green color, no matter how the eggs are
cooled. Since the yolk contains iron and a fairly large quantity of sulfur,
they wondered why the entire yolk did not turn green when cooked as long
as 7 hours. They found the sulfur compounds in the yolk were more stable
and less easily broken down to form hydrogen sulfide. Thus even with
long cooking the color of the interior of the yolk is not changed.
Custards
In custards, eggs are combined with milk and sugar. The chief protein
of cow's milk is casein, which is not coagulable by heat. Milk contains
some albumin and a small proportion of globulin, which are coagulable by
heat. Zoller states that the protein coagulable by heat is about 0.75 per
cent of cow's milk. In the mixed milk and egg, the egg furnishes the larger
percentage of the heat-coagulable protein. As the egg, milk, and sugar mix-
ture is heated, coagulation occurs, and the thickened mixture is known as
custard. If the temperature of the custard is carried a little higher than the
coagulation point, a point is reached at which the custard begins to show
syneresis, or the liquid separates from the curd. This is called the curdling
point.
Baked and soft custards. Custards may be cooked in two ways. They
may be cooked without stirring. This type is usually baked in the oven
and is called baked custard. The other type of custard is stirred continually
while it is cooked and is called soft custard. If the proportion of ingredients
in the custard are the same the one cooked without stirring is firmer in
texture and appears to be in one piece or clot. The soft custard has a softer
texture and is not in one piece but is a viscous fluid.
The stirred custard also tends to curdle more readily than the baked
344 EGG COOKERY
custard. In part, this is undoubtedly because of the effect of mechanical
agitation and is similar to the separation of fibrin of blood when beaten.
Milk for custards is often heated before mixing with the egg and sugar.
Forewarming of the milk may tend to prevent curdling of the milk, but
the greatest advantage is probably in shortening the cooking period.
Coagulation temperature of custards. The temperature at which
a custard begins to coagulate or thicken is higher than the temperature at
which the egg alone coagulates. The exact point at which coagulation starts
is more difficult to ascertain than in the egg white, since the coagulation
must be determined from the thickening of the custard. But not much
occurs below 80C. at ordinary rates of heating nor below 78C. at slower
rates of heating. As the soft custard coagulates, a thick layer will cling to
a spoon that is dipped into the custard. In cookery this is known as "coat-
ing a spoon" and is one method of estimating w^hen the custard is sufficiently
cooked. The temperature at which coagulation starts varies with the vary-
ing proportion of ingredients of the custard and the rate of cooking. In
class results, the coagulation of a custard made of 1 cup of milk, 2 table-
spoons of sugar, and 1 egg has never 1 been perceptible below 78C. and not
at this temperature except when the rate of cooking is very slow. Occa-
sionally a custard is heated slowly enough so that the best serving con-
sistency occurs at 80, provided the eggs are fresh so that the reaction has
not become quite alkaline.
It is possible to heat a cup of custard mixture in a double boiler from
room temperature to the curdling point in less than 3 minutes. With this
rapid rate of heating the custard is too thin to serve at 85 or even at
87 to 89, and generally curdles about 89, often after the temperature
has remained stationary at 89 for a time. It may reach 91 or 92 and
then drop back to about 89, the curdling occurring before a serving
consistency is attained.
When the custard is cooked more slowly, and particularly if the heat-
ing is slow after 75C. is reached, thickening is quite perceptible at 80,
it has a consistency for serving from 80 to 84 ; that cooked more slowly
being thicker at the lower temperature. A slower rate of cooking is pref-
erable to the rapid one. With the slower rate of cooking the thickening
is evident for considerable time before the curdling point is reached. With
the rapid cooking, the custard requires very close watching and rapid work
to remove it from the heat before the curdling temperature is reached.
Curdling may occur at 84 if the temperature is raised very slowly, but in
ordinary cooking it is more likely to occur between 85 and 87C.
Coagulation and particularly curdling in custards is accompanied by
absorption of heat. In the custards heated slowly the temperature is usu-
ally stationary for a considerable period before curdling occurs. In the
rapidly heated custards the temperature often reaches 90 to 92 and then
drops as curdling occurs.
The temperatures given in the following discussion are for custards
CUSTARD PIE 345
requiring 12 to 20 minutes from the time cooking is started to reach the
curdling point.
Concentration of egg and coagulation. If the proportion of egg
in the custard is increased, thus increasing the concentration of the protein,
coagulation starts at a slightly lower temperature, a firmer custard being
obtained at a definite temperature as the proportion of egg is increased.
Sugar. If the proportion of sugar to 1 egg and a cup of milk is increased,
the coagulation temperature is elevated and coagulation begins above 80C.
The elevation of coagulation temperature is proportional to the amount
of sugar added. If the custard is saturated with sugar, coagulation does not
occur at boiling temperature.
Yolks. If two yolks are substituted for 1 whole egg the coagulation
temperature is higher than for the whole egg.
Whites. If two whites are substituted for the one whole egg the coagu-
lation temperature is lower than for a custard made of the whole egg. With
both the yolks and whites the coagulation temperature varies with the pro-
portion of sugar used.
The optimum temperature for cooking custards. Williams has
reported that the curdling point for a custard made of 1 egg, 1 cup of milk,
and 1 tablespoon of sugar is 83.5C. When the proportion of ingredients
is varied the curdling point varies. If the proportion of egg is increased
the curdling point is lowered ; increasing the sugar elevates the curdling
point.
The temperatures given previously and those reported by Williams are
for soft custards. Baked custards may be cooked several degrees higher than
soft custards without curdling. This lower curdling temperature for soft
custards is probably due to the stirring, which increases the tendency for
separation of the custards into curds. Hence, it is important in making
soft custards to prevent heating after a certain temperature has been
reached. This can be accomplished by putting the cooking pan in cold
water or by pouring the custard into another utensil.
Between the temperature at which coagulation starts and the curdling
point is a temperature at which the custard has the best texture and flavor
for serving.
Williams has reported that the optimum temperature for custards made
of 1 egg, 1 cup of milk, and 1 tablespoon of sugar is 82.5C. When 2
yolks are substituted for the whole egg the optimum temperature is 83.5,
and when 2 whites are substituted for the whole egg the optimum tem-
perature is 82.
Custard pie. In cooking custard pie one of the major difficulties is
to prevent soaking of the crust. Increasing the proportion of egg helps,
as the custard then coagulates at a lower temperature. Thus \ l /2 eggs to a
cup of milk is better than 1 egg. Prewarming the milk before adding it to
the other ingredients shortens the time before coagulation takes place.
One way to prevent soaking of the crust is to cook the pastry and the
346 EGG COOKERY
filling separately. Bake the pastry on the bottom side of a pie pan with
sloping sides. Bake the custard in a pie pan of the same size as the one used
for the crust, setting the pan in hot water and using as low an oven
temperature as desired. After baking the custard, cool it until the pan feels
warm but not hot to the hand. At this temperature it has set sufficiently
to hold together, yet will not break so easily as when cold. Run a knife
or spatula around the edge of the custard and, tilting it at about a 45-degree
angle, shake and slide it out of the pan into the crust.
Whipping Eggs and Egg Whites
When an egg is whipped with an egg beater, or similar utensil, its vol-
ume increases, owing to incorporation of air. The egg white because of its
low surface tension and the stability of its surface films readily forms a
foam.
The essentials for a stable foam have been discussed in Chapter I. They
are a low surface tension, a low vapor pressure, and a tendency for the
substance in the surface to solidify, hence giving rigidity and permanence.
Stages of stiffness in beating egg whites. With slight whipping
the incorporated air bubbles are large, the egg white appears foamy yet
transparent, is very runny, and will flow readily. With longer beating the
air cells in the egg white become smaller, the appearance of the egg \vhite
is less transparent and more white. It still flows if the bowl is partially
inverted. The egg white becomes stiffer with continued beating. The stiff-
ness is due, in part at least, to the finer division of the air bubbles, and
thus the amount of egg white utilized in forming films is greater. Many
small air bubbles with their fine cell walls may be stronger and more
rigid than a few large cells. As beating is continued the egg becomes very
white, begins to lose a little of the moist, shiny appearance, and is stiff and
rigid. If the bowl is inverted, the egg w r hite does not flow but remains in
the bowl and the end of peaks stand up straight. If the egg is left to stand,
the watery fluid collects at the bottom of the bowl more slowly. With
longer beating the egg white appears dry, loses its shiny appearance, and
small white patches that look like small curds may appear. This is the
stage called dry in cook books. At this point the white is very rigid and
rather brittle so that with a w T hisk beater it is easily thrown out of the
bowl in which it is whipped.
Methods of testing stiffness. There are several ways in which the stiff-
ness may be tested. For household use the tests are ( 1 ) appearance, (2) the
height of peaks and the extent to which the point bends over when the egg
beater or some utensil is lifted out of the beaten white, and (3) the rate
of flow when the bowl or plate in which the white is beaten is partially
inverted. A skillful operator working constantly with egg white soon
learns to judge the degree of stiffness by these common household methods,
and the degree of proficiency that can be attained is surprising. But for
SALT AND WHIPPING OF EGG WHITES 347
experimental purposes the same degree of stiffness probably could not be
duplicated in another laboratory from the description. In the home the
height of the peaks, and particularly the extent the point falls over, is the
best criterion for judging stiffness. The rate of flow is not quite so good
unless the same quantity of egg white is always used, for a large quantity
must be beaten stiffer to flow at the same rate as a smaller quantity.
For laboratory purposes, (1) specific gravity, (2) foaming power, and
(3) the amount of drainage during a definite time are used to test the
stiffness and stability of the foam. Specific gravity is determined by divid-
ing the weight of a given volume of egg white by the weight of the same
volume of water at the same temperature. Barmore reports that foams with
specific gravity of 0.15 to 0.16 yield good angel cakes. Bailey calculated
foaming power by means of the formula :
where F = foaming power of egg white, V = volume of dish in cubic
centimeters, and W = weight of foam in grams. The specific gravity of
the original egg white was taken as 1.04.
The stability of a foam may be tested by putting a given weight of foam
in a funnel of known capacity and bore. The funnel is covered to prevent
evaporation. If the funnel is placed in a graduated cylinder, the drainage
may be read in cubic centimeters or the weight taken at the end of a
definite time, usually 30, 40, or 60 minutes. When the egg white is not
beaten sufficiently both the unbeaten egg white and the foam drain from
the funnel. After a certain stage of beating is reached little drainage
occurs. With still longer beating Barmore states the drainage increases.
Work of students in the author's laboratory, Keltner, Hoskey, and Loaft,
though not extensive enough to be conclusive, indicates that better angel
cakes are obtained if a certain percentage of drainage occurs, the exact
amount varying with different types of egg beaters.
Salt and the whipping of egg whites. It is traditional that a small
amount of salt added to egg white is an aid in increasing foaming and
stiffness. This could easily be tested but so far as the writer knows its effect
on stability has not been reported. It has been found that electrolytes are
necessary for heat coagulation of proteins. They may also aid coagulation
by mechanical means or surface denaturation. The more likely explanation
is the one previously given for protein solutions and electrolytes. The pro-
tein lowers the surface tension but the addition of salt lowers it still more,
thus causing a greater concentration of the protein at the air/liquid inter-
face, hence a slight stiffening. The addition of salt may result in a slight
salting-out effect and a stiffening of the membrane around the air bubbles.
This would have the same result as in emulsions. For, by the last mecha-
nism a certain amount of salt would bring about maximum stabilization
348 EGG COOKERY
of the emulsion or foam, but too large a quantity would have the tendency
to break the emulsion or the foam.
Acids and stability of egg white foams. Barmore in his last
publication states that when acid substances were added in sufficient quan-
tity to adjust the egg white to />H 8 the stability of the foam was prac-
tically the same for acetic and citric acids and for cream of tartar. But at
pH 6 the cream of tartar produced the most stable foam. The acid sub-
stances increased the stability of the foams.
The addition of the acid delays the formation of the foam, i.e., if beaten
for a definite time the foams containing acid are not as stiff as those con-
taining no acid. This is particularly true for both acetic and citric acids.
The addition of sugar to egg white foams. Adding sugar to the
egg white increases the stability of the foam, for less drainage occurs when
the egg is beaten to a definite stiffness. However, a longer time is required
to beat the egg white, if the sugar is added before the beating is completed,
but this also makes it difficult to overheat the foam. Because sugar retards
denaturation of the egg w r hite foam, it is a good practice to add sugar to
the egg \vhite as soon as beating is started when whites for angel cakes
are whipped at high speed on a machine. It would also appear that less
leakage might occur in meringues for pies if the sugar is added by beating
it into the \vhite as the white is beaten.
Egg white is partially coagulated during beating. In whipping
the egg white is finely divided, so that from the physical subdivision it
is far more rigid and stiff. But the beating has brought about other changes
in the egg white. In speaking of the methods by which coagulation may
be brought about, Ostwald states, "When egg white is beaten to a foam,
a part is regularly coagulated in the \valls enclosing the air bubbles. A
decrease in degree of dispersion to the point of inducing coagulation can
also be brought about through centrifuging, etc. These belong to the
mechanical methods of producing coagulation."
Effect of temperature upon whipping of eggs. Since a low sur-
face tension is one essential for the formation of a foam, it follows that a
lowering of the surface tension will aid its formation. Eggs that are taken
from the refrigerator and beaten while still cold do not whip up as readily
or quickly as those at room temperature. Surface tension is lowered with
increased temperature so that it is probably one factor in bringing about
this result.
The Bakery Research Department of Procter & Gamble Company have
reported that "regardless of the length of time of beating, a given sugar
and egg mixture, when whipped at 60F., will never become as light as
will a mixture of the same proportions beaten at the same speed and at a
temperature of 110F."
St. John and Flor found that a greater volume was obtained at room
temperature, about 21 C, than at refrigerator temperature, 13C. A still
better volume \vas obtained at 30C., but they report that while drying
EGG BEATERS 349
the whites to measure the volume the liquid part from those beaten at the
highest temperature separated more readily.
Season and age of eggs and whipping. The whipping quality of
eggs varies, according to the season in which they are produced. Nemetz
has reported experiments in which whole eggs that had been broken and
frozen in April, July, and September were used. The eggs were used in
sponge cake and cream puffs. With all mixing and baking conditions stand-
ardized, the April eggs gave a 15 per cent increase and the September
ones a 10 per cent increase in volume over the July eggs in sponge cake.
Similar results were obtained in cream puffs.
Burke and Niles found that egg whites from eggs produced during the
season when eggs are considered less desirable beat to a stiffer foam when
beaten the same length of time than the whites from eggs produced early
in the spring.
Nemetz states that if fresh or frozen eggs are used in a similar mix
under identical conditions, greater volume and greater yield will be obtained
from frozen eggs.
Bakers also claim that egg whites do not whip as well if used the next
week after being frozen as when they have been frozen at least three
months.
Barmore states that the older the eggs, when whites were beaten for
equal lengths of time, i.e., 1, 2, and 3 minutes, the less stable the foam.
However, when eggs were beaten 4 minutes the stability was practically
the same for all ages of egg used, e.g., fresh, 3, 6, and 9 days.
Egg beaters. Egg whisks or whips are made with wires of varying
thickness. The thick wire does not whip or divide the egg white as easily
as the finer wire. The air cells are larger than when a whisk with finer
wires is used, though the size of the enclosed air bubbles decreases with
longer beating with any type of beater. Whisks with thicker wires may
require two to four times as many strokes to beat an egg white to a definite
stiffness as one with finer wires. Some egg whisks beat the egg quickly,
dividing it into many very fine cells without giving an excess of the curdy-
looking precipitate within the whipped white. Some produce a greater
curdled appearance than others, even when the egg does not appear to be
beaten to the same stage of stiffness. With the type of whisk that produces
the very curdled appearance of the egg white, the cell walls of the omelet
or souffle are more likely to collapse during baking, and, by many cell walls
running together, a very coarse texture is obtained or the product falls.
The above statements regarding whisks also apply to egg beaters of the
rotary type. There is some variation in the width and the curvature of
the blades of these beaters.
If the quotation concerning emulsifying apparatus, from Clayton, in the
chapter on emulsions is changed to read, "It is quite reasonable to believe
that for any given egg beater there exists an optimum speed or degree of
agitation or beating, and an optimum time of beating, whereby the most
350 EGG COOKERY
perfect beaten egg white is obtained for a definite use," the statement may
apply equally to egg beaters.
Longer experience only emphasizes the importance of the foregoing quo-
tation from the chapter on emulsions. For instance, in the Foods Laboratory
a procedure had been worked out whereby excellent angel cake is made by
beating the egg white and adding the sugar, using high speed on the
Kitchen Aid. The beating must be timed to the second, because with
several hundred r. p. m. a few seconds too long makes a tremendous
difference.
When Peet and Lowe began work on starting baked products in cold
and preheated ovens, it was necessary to mix six times the angel cake
recipe at one time. But it was found that the time of beating the egg whites
on an institutional, large-sized Hobart mixer had to be increased over the
time used with the Kitchen Aid to have the same stage of stiffness.
Bailey obtained larger volume from the thick portion of the white than
from the thin part when whipped on a Hobart type mixer, but results
were opposite on an electric Dover type.
Barmore states that with hand rotary beaters there was more reduction
in viscosity for the corresponding reduction in specific gravity than with
the electric beater used in his experiments. It has been the experience in
this laboratory that Barmore's hand beaters 1 and 2 are poor types.
Hand-operated rotary beaters may be turned at varying speeds. But fast
initial beating of egg white gives a larger volume to the egg white.
The gear ratio for hand-operated rotary beaters is about 1 to 5, i.e., one
turn of the handle gives about 5 revolutions of the blades. If the handle
is turned 120 r. p. m., the blades would turn about 600 revolutions. The
speed of electric mixers, depending on the particular mixer, the speed, and
for some mixers the load or stiffness of material used, may range from 300
to 2400 r. p. m.
Wire whisks or rotary beaters. One question that is constantly asked
regarding the whipping of egg whites is whether it is better to beat them
with a whisk or rotary beater. A great deal depends upon whether the
egg whisk or rotary beater is a good type of its class or a poor one. If the
eggs are whipped so that the cells in the cake are the same size there
seems to be little difference in the finished product. Whisks sometimes
give a larger volume than rotary beaters in angel cake.
Combination of egg albumin with metals. Sometimes in beating egg
white a pink color develops. This is due to a combination of the egg albu-
min with a metal like copper or iron. The color develops more frequently
when the acid cream of tartar is added, as in beating egg whites for angel
cakes, but it may develop without its addition. Some egg beaters have
blades of copper that are plated. After the plating is worn off the copper
is exposed. The pink color has often been noticed when folding sugar into
the beaten egg whites with a spatula. Probably some other factor than the
presence of the metal alone is necessary to bring about the color change,
SOFT MERINGUES 351
for the color does not always develop when the egg whites are beaten with
such beaters or when spatulas are used.
Meringues
Meringues vary in the quantity of sugar added and in their use. Only
soft and hard ones will be considered here.
Soft meringues. One general use for soft meringues is for pies. The
factors determining to the greatest extent whether a desirable meringue is
obtained are : the extent of beating the egg white, the adding of the sugar,
the baking temperature and time, and an optimum proportion of sugar to
egg white. Good meringues have been obtained by many methods, but the
following method is successful for a majority of the experimenters. Beat
the sugar into the egg white preferably during the latter half of beating,
but it may be added at the start with a rotary egg beater, until the whites
are stiff and shiny. The peaks are fairly stiff and the tip end only slightly
rounded.
The sugar stabilizes the egg-white foam. Greater stabilization seems
to be attained when the opportunity for solution is greater, i.e., in beating
instead of folding. Since adding the sugar during beating increases the
time required for obtaining a definite stiffness, there is less danger of over-
beating. In some class problems less leakage of the meringue has occurred
when the sugar was added in the above manner.
Since leaky meringues give undesirable moistness and slipperiness to the
top of the pastry filling and make cutting difficult, how to prevent this
leakage is a question frequently asked. The Institute of American Poultry
Industries states that there seems to be no advantage in adding a small
amount of water to the meringue. Although water increases the volume,
there seems to be a tendency for the meringue to leak a short time after
baking.
Insufficient beating of the egg white, especially if the sugar is folded
instead of beaten into the meringue, after the sugar is added is sometimes
a factor in causing leakage. Over-beating of the egg white before sugar
is added may also increase the tendency to leakage.
Too small an amount of sugar to each egg white tends to give a less
fluffy, less tender meringue and one lacking in sweetness. Too much sugar
tends to give a gummy crust or one containing sugar crystals, though the
amount of sugar that can be used to obtain a desirable meringue depends
on the fineness of the sugar and perhaps on its rate of solution. In general,
2 tablespoons of fine or berry sugar per egg white give the best results.
With ultra-fine crystals, as many as 3 tablespoons of sugar per egg white
can be used; whereas with coarser granulated sugar, hitherto used more
than at present, less than 2 tablespoons per egg is desirable. Powdered
sugar containing starch is usually not satisfactory in meringues. Honey,
sirup, or jelly may be used in meringues, but only 1 tablespoon per egg
352 EGG COOKERY
white. Red jellies often give a blue rather than a pink tinge to the
meringue.
Baking necessarily requires a longer time at a lower temperature. All of
the following temperatures have been used successfully, though a majority
of the students working on meringues as special problems preferred 425
and 400F.: 425F. for 6 minutes, 400F. for 8 minutes, 350F. for 12
to 18 minutes, and 325F. for 18 to 25 minutes. With temperatures
below 325 F., the time is long, the meringue often shrinks after being
removed from the oven, and dries too much.
Hard meringues. Hard meringues contain a larger proportion of
sugar than soft meringues. Because of the high sugar content they have
a fairly smooth, somewhat crystalline, crisp crust. They are usually puffy
in appearance and are used for accompaniment to, as a foundation for, or
as a dessert.
The optimum amount of sugar appears to be 4 to 5 tablespoons per egg
white, the smaller quantity probably being preferable. Since acid increases
the tenderness of egg white, its addition is desirable. About 1 to 2 cc. of
vinegar per egg white may be used ; but, since cream of tartar produces
a more stable foam than acetic acid, the use of cream of tartar may be
preferable. About 1^2 per cent of cream of tartar, or between ]/$ to Y\
teaspoon of cream of tartar per egg white, is satisfactory.
The sugar is added in the same manner as for soft meringues, but,
because of the larger quantity added, better results are usually obtained
if it is added gradually.
Bake on heavy paper at as low a temperature as possible, 225 to 275 F.,
for 40 to 60 minutes, the time depending on the temperature and size of
the meringues. If the meringue is eaten shortly after baking, the soft
centers, if not entirely dried in baking, are not objectionable. However,
they may be removed. If the meringues are to stand over night, the Insti-
tute of American Poultry Industries recommends letting them stand in
the oven until cool, after the heat is turned off, in order to dry the centers.
Omelets
There are several types of omelets. They are designated in various ways
as plain, French, and foamy omelets. Some have a white sauce or tapioca
basis. In others, bread crumbs are used to absorb a part of the moisture.
The type of omelet that has the egg yolk folded into the beaten white is
sometimes called a foamy omelet. This is the type that requires the most
skill in making and is the one mentioned here.
Method of mixing foamy omelet. The yolk is beaten until foamy
and then folded into the stiffly beaten egg w^hite. The cooked omelet should
be light, tender, and foamy, and it should not collapse or fall after cook-
ing, though some shrinkage usually occurs. Whether the product obtained
fulfils these conditions depends to a great extent upon the amount of beat-
ADDITION OF LIQUID TO FOAMY OMELET 353
ing of the egg white, the mixing of the egg white and the yolk, and a
proper cooking temperature. The egg whites for omelets need to be
whipped nearly or quite stiff enough to stay in an inverted bowl. Unless
they are sufficiently stiff there is a tendency for the liquid to drain to
the bottom of the bowl or cooking pan. After the yolks are mixed with the
whites this tendency is increased. Sometimes the liquid portion does collect
in the bottom of the cooking pan and coagulates there while cooking, form-
ing a thick compact layer. This is due to insufficient beating of the whites,
or insufficient mixing of the yolk with the white, so that the yolk is not
sufficiently blended through the white to be held up by the framework
or physical structure of the whipped white, or it may be due to standing too
long after mixing before cooking is started. The pan into which the omelet
is poured should be hot enough to start coagulation of the egg, but not
hot enough to form a hard crust. However, over-mixing and rough han-
dling cause loss of too large a portion of the air incorporated into the
egg white. Over-beating of the egg white before the yolk is added results
in loss of extensibility, and the volume of the omelet does not increase as
much as it should during baking. It is also drier and sometimes powdery.
But with omelets it seems better to err a little on the side of over-beating
rather than under-beating.
Formation of ferrous sulfide in omelets. The green color develops
on the bottom of the omelet only when some of the egg has separated and
drained to the bottom. It is due to the formation of hydrogen sulfide from
the white and its combination with iron of the yolk. It may be prevented
by sufficient beating of the egg white, by thoroughly blending the yolk
and white, or by starting cooking promptly. The color may develop in
omelets cooked on top of the stove, or in those cooked in Pyrex, but occurs
more often in baked ones, for the baking requires a longer time.
Effect of addition of a liquid to a foamy omelet. A tablespoon
of water for each egg is usually added to the white or to the yolk. If to
the white of the egg, it may be added before the white is beaten or after
it is beaten enough to become frothy but not stiff. The volume of the
beaten white with the addition of the liquid is usually greater than an
egg white without the added liquid. Sometimes other factors due to size
of the egg, its deterioration in quality, or other causes affect its beating
qualities and a poor volume is attained. It has already been stated that
increasing alkalinity tends to prevent coagulation. Thus very old eggs may
not beat as well as fresher ones. The hydration of the white increases the
tenderness of the omelet as well as its elasticity. The white being more
elastic, a larger volume is obtained during cooking. If too much water is
added to the egg a point is reached at which the white becomes too tender
and too many cells break when the air expands during cooking. Evidently
the addition of water to egg white retards coagulation by beating, for a
longer time is required to beat the white to a definite stage than when no
354 EGG COOKERY
liquid is added. This retardation of coagulation may be due to the lessened
concentration of the egg white.
Kind of liquid in omelets. The liquid added to foamy omelets may
be water, vegetable juice, tomato juice, or a mixture of one-third lemon
juice and two-thirds water. If a tablespoon of milk is added to an egg white
it will not form a foam. If added to the beaten white the volume is quickly
reduced and the foam is destroyed. Dizmang and Sunderlin investigated
the effect of milk on the whipping quality of egg white. Their results are
given in Table 42, and indicate that the fat of the milk is responsible lor
breaking the foam. But the size of the fat globules is also important,
smaller particles having less effect.
TABLE 42
THE EFFECT OF MILK ON WHIPPING QUALITY OF EGG WHITES
(Dizmang and Sunderlin}
Largest number of drops added to
Substance added to one egg white, permitting formation
egg white of foam stiff enough to stay in an
inverted bowl
Cream (20% fat) 1-2
Whole milk 2-3
Sterilized whole milk 8
Reconstituted pow T dered whole milk 50-70
Cream (20% fat) homogenized, 3000 Ibs. . . 70
Evaporated milk 50-350
Separated milk 400-446
Whole milk, homogenized, 2500 Ibs 400-450
Whole milk homogenized at 3000 Ibs 1000
Reconstituted powdered separated milk. . . . 1600
The addition of 1 teaspoon of lemon juice and 2 teaspoons of water to
an egg white brings the reaction to about />H 4.8, the isoelectric point
of the egg albumin. It may be higher or lower, depending on the original
/H and perhaps the size of the egg. The addition of a tablespoon of tomato
juice to an egg white does not lower the />H to 4.8. The addition of tomato
juice and the lemon juice results in a more tender omelet, and one of
greater volume, if the conditions of mixing have been standardized, if the
liquid is added after the egg white is partially beaten, and if beaten to the
same degree of stiffness. Tomato juice requires longer for whipping than
the water, and the mixture of lemon juice and water requires still longer
than the tomato juice. The addition of the acid tomato and of the lemon
lessens the alkalinity of the egg white. Bogue has reported that the foam-
ing properties of gelatin are greatest at the isoelectric point. If the foaming
properties of egg white are also greater at the isoelectric point, a greater
REVIEW OF LITERATURE ON ANGEL CAKE 355
volume might be expected at pH 4.8. This greater volume is usually
obtained, with the addition of tomato or lemon juice, but a longer whipping
time is required. Tomato and lemon both contain citric acid. The greater
tenderness with the use of tomato juice and lemon juice probably results
from a peptizing effect of the citrate ion on the egg protein. If lemon juice
is merely added to egg white without whipping it, coagulation of the egg
white is produced, but with beating the lemon juice is thoroughly mixed
with the egg white. A better volume is usually obtained if the egg white
is beaten until frothy before the lemon juice or tomato juice is added.
Temperature for cooking omelets. Omelets are usually cooked above
heat, but baking them in the oven is an easy method to secure uniform
temperatures for class work. A temperature of 160 to 165C. is a good
one to use. If the temperature is too low the omelet tends to separate while
cooking, the liquid portion collecting in the bottom of the cooking utensil
and forming a solid mass with the foamy part on top. Too high a tempera-
ture for cooking leaves the inside of the omelet too moist unless the outer
portion is over-cooked and thus toughened. In cooking over the heat the
omelet needs to be covered. The omelet can be placed under the broiler to
brown the top quickly.
Angel Cake
Angel and sponge cakes are included under egg cookery because they
logically belong here and not under batters and doughs. The texture of the
finished cake depends chiefly upon the manipulation of the egg, and the
cooking temperature corresponds to that used for egg cookery.
Review of literature on angel cake. Excellent work has been
reported from different laboratories on angel and sponge cake and a review
of this literature seems rather imperative.
Hunt and St. John separated the thick and the thin portion of egg
whites. The average volume of the cakes from the thin portions was greater
than for the cakes made from the thick portions. They have also reported
that the volumes of angel food cakes made from egg whites beaten at
room temperature, 21 C., were larger than cakes made from similar whites
beaten at 5C. The grain of the cakes made from whites beaten at room
temperature was finer and the cakes more tender than those from whites
beaten at 5C.
Hedstrom, in studying the effect of the consistency of the egg white on
the volume and texture of angel cakes, found the percentage of thin white
increased, as did the pH, with increased age of the eggs. The effect of age
of the eggs on the volume of the cakes is shown in Fig. 35. It is obvious
that there are some discrepancies in these results. Nevertheless, they are
given here, for further work, which is not complete, appears to substantiate
these results in that cake volume decreases with increased age of the eggs.
356
EGG COOKERY
Barmore's results of investigating the influence of chemical and physical
factors on egg-white foams are as follows: stability of the foams was
determined by beating the egg white with an electric food mixer and
photographing the foams 2 and 10 minutes after beating had stopped. The
specific gravity of foams was determined. Stability of the foams was further
determined by placing the egg-white foam in a funnel and determining the
drainage at definite intervals.
620
610
600
1590
JsTO
>560
<u
530
<520
510
500
490
\
\
\
- Average of Seven
or More Cakes
Average of Less
Than Seven Cakes
8 12
16 20 24 28 32 36 40 44 48 52
Age of Eggs in Days
FIG. 35. Relation of angel cake volume to the age of the eggs. (Hedstrom.)
It was found that the older the eggs, the lighter the specific gravity of
the foam after beating for a definite period of time. The addition of
potassium acid tartrate, citric, and acetic acid increased the stability of the
foams. The longer the foam is beaten, the less stable it becomes so that its
stability is inversely proportional to its specific gravity.
Stanley states that the thin white beats up to a larger volume than the
thick white. But the volume of the cake made from the thick white is
larger than that made from the thin white and cakes made from the
thick white have greater elasticity.
Barmore reported from his investigations o'n baking angel cake at various
altitudes that increasing the egg or flour, or both, in an angel cake in-
creases its tensile strength. Conversely, increasing the sugar decreases the
tensile strength or increases the tenderness. Barmore says that his formula,
F-. 43S - A\A + 24.5 = 0,
gives all the possible, successful recipes for this type of flour mixture for
REVIEW OF LITERATURE ON ANGEL CAKE 357
any habitable altitude. F represents flour in grams ; S, sugar in grams ; and
A, altitude in thousands of feet. The egg white was kept constant at 210
grams and the flour should be not less than 40 nor exceed 80 grams for
this proportion of egg white. For 1 gram of egg white this allows 0.19 and
0.39 gram of flour respectively.
King, Morris, and Whiteman investigated "some methods and apparatus
used in measuring the quality of eggs for cake making." The physical and
chemical measurements made on the eggs were carbon dioxide content of
the white and the yolk, />H and total solids on white, yolk, and magma,
and viscosity of the magma. They say more work should be done on the
relation between CO 2 content and pH. before it can be said that the
increase in />H of the white is due entirely to a loss of CO2. The lifting
power of the eggs was based on measurements of specific gravity and />H
of the cake batter and on volume, tensile strength, and compressibility of
the sponge cakes. They report that the chemical and physical properties
of the eggs so far measured have shown no definite relation to the various
cake measurements.
Barmore determined "the influence of various factors, including altitude,
in the production of angel food cake." He concludes that the whites of
fresh eggs should be beaten with 1 to 2 per cent of cream of tartar to a
specific gravity of not less than 0.15 and not more than 0.17. Part or all
of the sugar should be added before the addition of any of the flour, for
the addition of the sugar strengthened the egg-white foam; whereas the
volume of the batter decreased considerably more when the flour was
added with the sugar than when it was added by itself, after the sugar
had been beaten into the egg foam. A summary of Barmore's extensive
investigations follows :
At />H 8 the stability of the egg-white foam was practically the same
for acetic and citric acids and cream of tartar. But at /H 6 the cream of
tartar produced the most stable foam.
Cakes baked at 178C. for 30 minutes had larger volume, were more
moist and more tender, probably because of larger volume, than cakes
baked at 163, 152, or at 138C. The last required 100 minutes for
baking. Baking at the highest oven temperature produced an interior tem-
perature about 2C. higher than in cakes baked at the lowest temperature,
though the difference in oven temperature was 40C.
Eggs several days old made poorer cakes than fresh eggs. The reason
suggested for this is hydrolysis of the egg proteins rather than increased
proportion of thin whites.
No moisture was lost by evaporation by any portion of the cake farther
from the outer edge than 1 cm. "Cake baked at the low temperature
appeared to contain less moisture, because the center of the cake felt and
tasted much drier than that baked at a higher temperature for a shorter
358 EGG COOKERY
time. The data show that one was just as moist in the center as the other.
The difference in feel was apparently occasioned by the difference in the
condition or location of the moisture. Perhaps in the lo\v-temperature cake
the moisture had been more completely removed from the sugar solution
and absorbed by the starch or protein, because of the greater length of
time the cake was maintained at a high temperature."
In studying the influence of acid and sugar on the initial coagulation
temperature of egg white (different proportions of sugar and acid added to
egg \vhite, placed in test tubes for heating) it was found that sugar in-
creased but acid lowered the initial coagulation temperature of the egg
white. Adding both sugar and acid in proportions used in cakes raised the
temperature at which coagulation of the egg white started. However, in
spite of the lowered initial coagulation of the egg white by the addition of
acid, its addition increased the tenderness of the egg white. In the test with
egg white coagulated at various temperatures it was found that the lower
the temperature at which coagulation occurred the more tender the egg
white.
"With increases in altitude it has been shown that the amount of expan-
sion during baking increases; the cake becomes more tender; the final cake
volume changes and is related to tenderness; the amount and rate of
evaporation increases; the maximum internal cake temperature decreases;
the volume of the vapor escaping increases; and the color of the crust
becomes lighter."
Peet and Lowe baked angel food cakes in six ranges, three electric, two
gas, and one kerosene. Cakes were baked in ranges cold at the start and in
preheated ovens.
The results of analysis of scores showed that the judges did not dif-
ferentiate among cakes baked in the different ranges for total score, texture,
and eating quality. However, for these same points the judges thought
the cakes baked in the preheated ovens were superior to those baked in the
same ranges from a cold start. Furthermore, these differences, as shown by
analysis of variance, were highly significant.
The scores for moistness were higher for cakes baked in preheated ovens
but these results were not analyzed statistically.
Tenderness was tested in two ways, one subjective and one objective
test. The analysis of scores for tenderness indicated that the cakes baked
in some ranges were more tender than cakes baked in other ranges. The
statistical analysis showed that these results were significant. The judges,
as indicated by scores, considered there were still greater differences in
tenderness of cakes baked from a cold and from preheated starts, than for
cakes baked in different ranges. These results were highly significant, the
cakes started in preheated ovens being tenderer than those baked from a
cold start. The analysis of data obtained by tensile strength measurements
also indicated significant differences in tenderness of cakes baked in dif-
REVIEW OF LITERATURE ON ANGEL CAKE 359
ferent ranges and highly significant differences between cakes started in
cold and preheated ovens, those started in preheated ovens being more
tender. The correlation coefficient between the two methods of testing ten-
derness was .4014, which was significant. This indicates that in general
there was agreement in the two methods of testing tenderness.
The volumes of cakes varied in the different ranges, the results being
significant, i.e., cakes of larger volume were obtained in some ranges than
in others. The volumes of cakes baked in preheated ovens were greatest,
and the differences were significant.
Burke and Niles made angel food cake on the same day of the week
throughout the year, from eggs of the same age, produced by the same
flock on controlled feed for the duration of the experiment. The quality
of the cakes, at first fairly good, decreased to a low in November. After
a slight rise in December there was again a decline in January. A notice-
able increase in quality occurred in February and March. They state that
the egg-white foams during the "low" and "high" periods seemed to differ
in the time required to beat to the stiff stage. During the "low" period the
whites seemed much stiffer and less tender than those in the "high" when
beaten for the same length of time. They state that perhaps, if the amount
of beating were standardized according to some factor other than time for
beating, excellent cakes could be made during the "low" months as well as
the "high."
One cake each week was baked at 350F. for 45 minutes, and three
cakes at 325 F. for 1 hour. Consistently throughout the year the moisture
loss was less and the volume usually noticeably larger for the cakes baked
at the higher temperature. The average moisture loss for the year was 11.2
and 9.6 per cent, and the average volume 7.79 and 7.85 cm., respectively,
for cakes baked at 325 and 350F.
King, Whiteman, and Rose investigated the effect on the cake-making
quality of some egg-production factors. The physical and chemical measure-
ments of eggs, cake batter, and sponge cake were the same as those reported
for King, Morris, and Whiteman, with the exception that elasticity or
recovery of the cake crumb is added in the present study. They found that
five different diets of the hens did not affect the properties of the eggs or
the quality of the cake made from them. Most of the eggs used were
obtained over a period of seven months (December- June), beginning about
three months after the hens started laying, and were collected and dipped
in mineral oil saturated with carbon dioxide. They found no progressive
change in the properties of the eggs or the quality of the cakes over the
period in the laying cycle of the hen or the seasons of the year studied. As
in the earlier study they found no apparent relationship between the physi-
cal and chemical properties of the eggs studied and the quality values of
the cakes.
360
EGG COOKERY
"There was a relationship between the specific volume, elasticity, and
compressibility of the sponge cakes, and between the pH and specific
gravity of the batter from which the cakes were baked.
"Findings of an earlier study which indicated that there is no relation-
ship between />H and CO 2 content of egg white were confirmed."
Formulas for angel cake. Because formulas mean more to many
cooks than equations, the data in Table 43 have been compiled.
TABLE 43
FORMULAS FOR ANGEL FOOD CAKE
Egg white
Sugar
Flour
Cream
Amount
Formula
Meas. Wt.
Meas. Wt.
Meas. Wt.
of
of
Cups Gm.
Cups Gm.
Cups Gm.
tartar
salt
I .
1 244
\% 250
1 100
1 t.
x*.
II ....
1 244
\y 2 300
1 100
1 t.
x .
Ill ....
IK 366
\y 2 300
1 100
-L / /2 t .
y 2
IV ....
\y 366
IX 250
4/5 80
1
y, -
V . ...
IX 427
\y 2 300
1 100
2 .
y> .
VI ....
1 244
1 200
1 100
1
x
VII ....
1 246
23i6 266
% 90
1
X t.
VIII ....
1 246
1% 169
y 48
1
Xt.
IX ....
1 246
\y 222
% 90
1
x*.
Only the first five formulas have been made in class work at 900-feet
elevation. Excellent cakes may be made from these five formulas, though II
is less likely to be successful. The last three formulas are from Barmore's
tables; VII and VIII are for 1000-feet elevation with the largest and
smallest amounts of flour advocated, respectively. Further analysis of these
formulas is found in Table 44.
Since sugar tends to prevent coagulation of the egg white, there is an
amount of sugar which, if exceeded, will prevent coagulation to such an
extent that the cake is so tender it will fall. It is desirable to use an amount
that will just prevent the cake from falling. However, this particular
amount of sugar will depend somewhat upon the amount of flour. The
flour increases the toughness of the cake. Hence there is a ratio of sugar
to flour, so that, within certain limits, as the sugar is decreased the flour
must also be decreased. For the formulas given the ratio of sugar to flour
is 3 to 1 in four of the recipes and 2.5 to 1 in the standard recipe.
The illustrations are all for angel cakes which were baked from the
same quantity of material, one-sixth of the recipe. The pans were small
ones so that the photographs are nearly actual size. Thus the illustrations
BEATING EGG WHITES FOR ANGEL CAKE
361
TABLE 44
AMOUNT OF SUGAR AND FLOUR PER GRAM OF EGG WHITE AND RATIO OF SUGAR
TO FLOUR (ANGEL CAKE)
Formula and source
Egg white
Gm.
Sugar
Gm.
Flour
Gm.
Ratio of sugar
to flour
I Standard
1
1.02
0.41
2.5
II
1
1.23
0.41
3.0
III Thirteen egg
0.82
0.27
3.0
IV Cedarquist
0.68
0.23
3.0
V Prize (LA. P. I.)*
70
0.22
3.1
VI Hunt and St. John
VII Barmore (1000 ft.)
VIII Barmore (1000ft.)
IX Barmore (5000 ft.)
1
1
0.82
1.08
0.69
0.90
0.41
0.36
0.20
0.36
2.0
2.9
3.5
2.5
* Institute American Poultry Industries,
show the comparative volume of the cakes, and the cells are nearly actual
size.
Beating the egg whites for angel cake. The beating of the egg
whites is one of the important steps in making angel cake. For the best
results, the whites should not be beaten quite as stiff as for foamy omelets
and souffles. The probable reasons for this are the stabilizing influence of
sugar on the egg-white foam and the absorption of moisture by the flour.
If the egg whites are not beaten a cake of small volume and very soggy
texture is obtained. When the egg white is beaten the volume of the cake
increases with the degree of stiffness of the whites, until a stage is reached
at which the greatest volume is attained. Continued beating of the egg
white after that to produce the maximum volume gradually reduces the
volume of the cake, the reduction in volume being in proportion to the
amount of over-beating of the egg white. The influence of the extent of
beating the egg white on the volume of the cake is shown in Figs. 40 and
41, Experiments 69,C and E.
Result of insufficient beating of the egg white. The egg whites for the
cakes in Fig. 40, Experiment 69C, were all beaten together. One-third
of the total weight of the egg white was removed for cake 1 after the egg
whites were beaten until they flowed when the bowl was partially inverted.
The volume is less than when the whites were beaten to flow very slowly
for cake 2. When the egg whites are whipped too little, not as much air
is enclosed and the film of egg white surrounding the air bubbles is not
as thin as it is with longer beating. If the egg white is beaten still less
than for the illustration, the volume is still smaller. With very little beat-
ing, the egg white is quite runny and the cake is tough and compact.
362
EGG COOKERY
Occasionally a gummy layer is found in the bottom of the baked cake. It is
often difficult to give an explanation for this, but it may sometimes be due
to insufficient whipping of the egg whites.
Maximum beating of the egg white. The whites for the cakes in Fig.
37, for cake 2, Fig. 40, and for cake 1, Fig. 41, were beaten until the
tip end of peaks was slightly rounded and fallen. The cakes are more
tender and have a larger volume than when the whites are not beaten
sufficiently. The appearance and stiffness of the egg whites for a maximum
volume in the cake vary slightly with the type and kind of egg beater used.
FIG. 36. The bowl on the right with the sloping sides is a good type for mixing
and folding.
The bowl on the left has sides that are too straight for efficient folding.
The spatula on the right has a round handle that fits the hand.
The spatula on the left has 4 edges that tend to blister the hand with long folding.
With a maximum volume of the cake the cell walls are thinner, which
tends to produce a more tender cake.
Effect of over-beating the egg white. For cake 3, Fig. 40, the egg whites
were beaten until quite stiff. The volume is decidedly less than for cake 2.
Longer beating results in a still smaller volume, see cake 3, Fig. 41. The
smaller volume with over-beating is due to excess coagulation of the egg
white by beating. This lessens the elasticity of the egg white ; hence, when
the air bubbles enclosed in the beaten egg white expand from the heat
during baking, some of the cell walls rupture instead of expanding. When
a number of the cells rupture during baking, several cell walls coalesce, the
cell walls are thicker, and the volume is reduced.
Mixing angel cake. After the egg whites are beaten the other ingre-
dients are folded into the cake. The water, cream of tartar, and the salt are
added to the partially beaten egg whites. The flavoring may also be added
to the egg white at the same time as the cream of tartar. This eliminates
extra folding after the sugar and flour are added. For directions for fold-
ing, see Experiment 68 ; and for types of bowls, Fig. 36.
MIXING ANGEL CAKE 363
Sugar. The sugar may be folded into the egg whites after they are
beaten or whipped with the whites. The latter is sometimes called the
meringue method. A certain amount of folding of the sugar with the egg
white results in a cake of the best texture and tenderness. Too little folding
does not blend the sugar sufficiently with the beaten whites ; then the flour
does not fold in readily and heavy spots may be found throughout the
cake. They may be quite small, but soggy and thick, and sometimes they
contain just a trace of dry flour in the thickened spot. Such a spot is shown
in Fig. 37, cake 1. The cakes usually increase in volume with longer folding
of the sugar, reaching a maximum with about 60 strokes; then a slight
decrease occurs with longer mixing. Sometimes the maximum volume occurs
after folding about 40 strokes and sometimes after about 80 strokes. The
tenderness of the cakes usually varies more with longer folding of the sugar
than the volume.
When the sugar is whipped into the whites, it may be added before
whipping is started but this materially lengthens the time for whipping. The
preferable time for adding the sugar is after the cream of tartar and salt
are added. The sugar is added gradually for hand beaters and the whites
beaten until stiff and shiny. The peaks stand up with slight rounding or
bending of the tip ends.
The meringue method is particularly good to use with an electric beater,
for the rapid revolutions can soon over-whip the whites to the dry stage.
Adding the sugar during whipping of the whites increases the time for
beating but also tends to prevent mechanical coagulation and tends to pre-
vent leakage, thus stabilizing the foam.
In class work about nine times out of ten better results are obtained if all
or at least half of the sugar is added to the egg white before any of the
flour is added. Barmore reports the same result. Yet one person that the
writer knows who makes excellent angel cakes always mixes all the sugar
and flour together and then adds it to the egg white. It illustrates a point
that constantly impresses all who have a chance to observe different people
work with foods. There is no one method that always produces the best
result. It seems best to give the method or methods successfully used by
the majority.
However, adding about three-fourths of the sugar to the egg whites and
sifting the remainder with the flour make the flour easier to incorporate.
Hence, the flour can be added with less folding with the result that tough-
ness is not increased from long folding and the volume of the foam is not
materially reduced. Mixing the sugar and the flour before adding to the
egg white has not produced as satisfactory results as folding the sugar first.
As one student remarked, "The addition of the sugar to the egg white
seems to prepare the egg for blending with the flour."
Flour. The flour is folded into the mixed sugar and egg white. Here
the amount of mixing also affects the volume and tenderness of the cake.
Too little mixing does not blend the flour sufficiently with the sugar and
364
EGG COOKERY
FIG. 37. Angel cake. Showing effect on the volume and texture of varying the
folding^of the sugar with the egg white. Cake flour used. Experiment (69,A). As
shown in the illustration the cakes are about five-sixths actual size.
FIG. 37.
1. The sugar folded
2. The sugar folded
3. The sugar folded
4. The sugar folded
5. The sugar folded
6. The sugar folded
20 strokes.
40 strokes.
60 strokes.
80 strokes.
120 strokes.
180 strokes.
366
EGG COOKERY
FIG. 38. Angel cake. Showing effect of substituting bread flour for cake flour in
Fig. 37. Experiment (69,E).
MIXING ANGEL CAKE
367
FIG. 38.
1. The sugar folded
2. The sugar folded
3. The sugar folded
4. The sugar folded
5. The sugar folded
6. The sugar folded
20 strokes.
40 strokes.
60 strokes.
80 strokes.
120 strokes.
180 strokes.
368
EGG COOKERY
FIG. 39. Angel cake. Showing effect on volume and texture of varying the extent
of folding the flour with the sugar and egg white. Experiment (69, B). As shown
in the illustration the cakes are about five-sixths actual size.
1. The flour folded 40 strokes.
2. The flour folded 60 strokes.
3. The flour folded 80 strokes.
MIXING ANGEL CAKE
369
2 I
FIG. 40. Angel cake. Showing effect on the volume and texture of beating the
egg white to different stages of stiffness. Experiment (69,C). As shown in the
illustration the cakes are about five-sixths actual size.
1. Egg white slightly under-beaten.
2. Egg white beaten sufficiently.
3. Egg white slightly over-beaten.
370 EGG COOKERY
egg white mixture, and the grain is coarser. Spots of flour may occasionally
be found. These are more likely to occur when the sugar has not been
sufficiently mixed, or when all the flour is sifted over the cake at one time,
or if too thick a layer is used, which increases the difficulty of incorporating
the flour, as it tends to pile and roll up in balls. Longer mixing of the flour
with sugar and egg white tends to produce a fine grain and small cells.
See Fig. 39, cakes 2 and 3. The longer mixing of flour also has a tendency
to toughen the cake, which may be due to development of the gluten of
the flour and to the thicker cell walls caused by combining several cells
through loss of air by mixing. An amount of mixing of the flour just to
blend it well with the egg white and sugar usually produces the best
results.
Texture. The texture and grain, also the volume and tenderness, of
angel cake are influenced by several factors : ( 1 ) The mechanical treat-
ment, which includes the kind of beater used, the degree of whipping of
the whites, the method of and extent of mixing the ingredients; and (2)
the ingredients used, their amount and kind.
The factor determining the size of the cells to the greatest degree is the
type of beater used and the extent to which the egg white is beaten, which
has been considered. Longer whipping produces more and smaller air bubbles
so that the cells are smaller, the grain finer. Rotary and electric beaters,
in general, give finer grain than whisks.
Beating the egg whites to obtain the possible maximum cake volume
usually produces the most tender cake, for with a maximum volume the cell
walls are stretched to the greatest extent, hence are thinnest.
The method of folding or mixing also affects the grain of the cake.
After egg whites are whipped, the folding and mixing should be done
gently and to retain as many of the air bubbles as possible.
Longer mixing of the sugar with the egg whites tends to give a finer
grain (see Fig. 37), but not to the extent that the folding of the flour
does. Thus the grain or texture of the cake may vary to a certain extent,
but a cake with thin cell walls and medium-sized cells that is so tender
that it "melts in your mouth" is preferable to one that has a fine grain but
is less tender.
Ingredients used in angel cake. Flour. The amount of flour per
gram of egg white may vary from 0.2 to 0.4 gram. The smaller amount
tends to give a more moist and tender cake, the larger a more dry and less
tender one. Cake flour produces a more tender cake than bread flour. It
contains gluten that is not so tenacious, and therefore yields a cake that is
more tender and of greater volume. The cakes made of bread flour shrink
and pull away from the pan as they finish baking and while cooling. See
Fig. 38, which is a reproduction of the manipulation and proportions for
the cakes in Fig. 37. It is possible to obtain a fair cake from bread flour,
but it is not as tender as with cake flour. Better results are obtained with
bread flour if the sugar is increased by about 2 to 4 tablespoons or the
INGREDIENTS USED IN ANGEL CAKE
371
^MpE
?
FIG. 41. Angel cake. Showing effect of increasing the sugar from 1^4 to \ l /2
cups. Typical sugary crust. Experiment (69,F). As shown in the illustration the
cakes are about five-sixths actual size.
1. Egg white beaten to flow slowly in a partially inverted bowl.
2. Egg white beaten stiff enough to stay in an inverted bowl.
3. Egg white beaten until very dry and flaky.
372 EGG COOKERY
flour reduced by about 2 to 4 tablespoons. There is also a greater tendency
for drops of sirup to collect on the surface of the crust when bread flour
is used.
Liquid. There does not seem to be any advantage in adding about 30 cc.
of water to the egg white.
Cream of tartar. Angel cake made without cream of tartar is cream
colored. The cream of tartar produces a very white cake on account of
the effect of the acid salt on the flour. The flavone pigments of flour are
cream colored when slightly alkaline but white when the reaction is acid
or neutral. Also the addition of cream of tartar produces a more tender
cake. Evidently the tartrate ion brings about peptization of the egg or flour
proteins, or both. Increasing the quantity of cream of tartar beyond the
amount used in the recipe produces a more tender cake and one that is
more moist and tart in flavor. Barmore recommends that the amount of
cream of tartar should be 1 to 2 per cent of the weight of the egg white.
The amount given in the standard recipe is about 1.5 per cent.
Sugar. A fine crystalline sugar, such as fruit or berry sugar, w^hich dis-
solves rapidly is excellent to use in angel cake. The maximum amount of
sugar per gram of egg white is about 1 gram. At higher altitudes this must
be decreased. At sea level, or up to 1000 feet above sea level, the sugar
can be increased to 1.25 grams of sugar per gram of egg white provided
the maximum amount of flour is used. But it must be handled carefully.
See Fig. 41. Cakes with large proportions of sugar have a typical sugary
crust.
Temperature of baking angel cake. Reports of recent investiga-
tions of baking temperatures for angel cake indicate that higher tempera-
tures than those commonly used are preferable. Barmore reports that cakes
baked at 178C. (352F.) had a larger volume, were more tender (prob-
ably because of larger volume), and appeared more moist, though a moisture
analysis showed no cakes lost moisture farther from the edge than 1 cm.
Burke and Niles have reported a larger volume, more tender cakes,
and less moisture loss for cakes baked at 350F. than for those baked at
325 F. Peet and Lowe have reported a larger volume, more tender cakes,
and more moist cakes when the cakes were baked in preheated ovens of
electric, gas, and kerosene ranges than from a cold start in these same
ranges.
Whether still higher temperatures will be more desirable has not been
reported. At present it appears that oven temperatures of 175 to 180C.
are preferable to 150 or 160C.
Sponge Cake
Sponge cake, like angel cake and foamy omelets, depends chiefly upon
the extent of whipping the egg whites, the mixing, and good proportions to
produce a tender cake.
REFERENCES 373
Probably the most common fault in making sponge cake is insufficient
beating of the egg yolks and sugar. These two ingredients, plus the liquid,
if water or lemon juice is used, can be beaten until they are extremely
light and foamy. This is most successfully done with rapid beating, prefer-
ably by an electrically operated beater or a rotary beater rather than a
whisk. Excellent sponge cakes may be made from only the yolks, provided
some water is added and the yolks and sugar are beaten rapidly until very
light. In the type of sponge cake recipe given in Experiment 70, when the
flour is mixed too long with the sugar and egg yolks the cake is more com-
pact and tough. But in some types of sponge cake in which considerable
water is added, that is, the ones called water sponge, it is often necessary
to beat the flour and egg yolks a long time to obtain a cake with thin cell
walls and a uniform texture. In other words, this can be interpreted to
mean that, for each recipe in which the proportion of ingredients varies
from those in another recipe, the amount and the kind of manipulation to
produce a cake of the best texture vary.
Different methods of combining the ingredients may be used in mixing
sponge cake. Several are suggested in Experiment 70. Excellent sponge
cakes may be made by any method of mixing. The method of adding the
water and lemon juice to the sugar, given in Experiment 70,3, produces
rather uniform results when used by many different students.
Platt and Kratz have reported means of measuring and recording some
characteristics of test sponge cakes, which can also be used with angel
cake. These include measuring tensile strength, volume, and specific gravity.
Whether the temperature for baking sponge cake like that for angel
cake should be increased has not been reported. It has been shown in the
author's laboratory that sponge cake made from egg yolks only is more
desirable when baked at 350F. than at 325 F. It is likely that most
sponge cakes should be baked at the same temperatures as angel cake.
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374 EGG COOKERY
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Burke, E. A., and Niles, K. B. A Study of Seasonal Variation in Egg White
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Clayton, W. The Theory of Emulsions and Their Technical Treatment. Third
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Egg White during Egg Formation. Poultry Sci. 15: 349 (1936).
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Jellinek, --. Item, Science 80: 10, Supplement, Aug. 31 (1934).
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King, F. B., Whiteman, E. F., and Rose, W. G. Cake Making Quality of Eggs
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Lepeschkin W. W. The Heat Coagulation of Proteins. Biochemical J. 16: 678
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Lorenz, F. W., and Almquist, H. J. Seasonal Variations in Egg Quality. U. S.
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Mattikow, M. A Critical Review of the Literature on the Coloring Matter of Egg
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REFERENCES 375
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Meyer, B. H. The Gelatinization of Egg Sols in the Presence of Electrolytes. Un-
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Ostwald, W. An Introduction to Theoretical and Applied Colloid Chemistry.
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Palmer, L. S., and Kempster, H. L. The Influence of Specific Feeds and Certain
Pigments on the Color of the Egg Yolk and Body Fat of Fowls. J. Biol.
Chem. 39: 331 (1919).
Peet, L. J., and Lowe, B. Starting Baked Products in Cold Versus Preheated
Ovens. Research Bulletin. Iowa State College, Agri. Expt. Sta. (1937).
Perry, F. D. Influences of Rations and Storage on the Physical Characteristics
of Eggs. Iowa State College, Agri. Expt. Sta., Research Bulletin 192 (1936).
Platt, W., and Kratz., P. D. Measuring and Recording Some Characteristics of
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Procter & Gamble Co., The. Better Cakes, Crisco Bakery Service, Series No. 6.
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Rahn, O. Why Cream or Egg White Whips. Food Ind. 4: 300 (1932).
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Schaible, P. J., Moore, J. M., and Davidson, J. A. A Note on the Structure of
Egg White. The U. S. Egg and Poultry Mag. 41: 38, Dec. (1935).
Sharp, P. F. The />H of the Whites as an Important Factor Influencing the
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Sharp, P. F. What a Week May Do to an Egg. The U. S. Egg and Poultry Mag.
35: 14 Jun. (1929).
Sharp, P. F. Opportunities for Chemical Research in the Poultry Industry. The
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376
EGG COOKERY
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(1937.)
EGGS
Cooking Eggs in Water
Experiment 63.
I. In the shell.
A. To determine the effect of coagulation at different temperatures on the
texture of the white and yolk.
1. Cook an egg in water. Do not let the temperature of the water go
above 72C. It is easier to control the temperature, if a large quantity of
water is used and the heat is turned low after the desired temperature is
reached. Cook from 1 to \ l / hours.
2. Cook an egg in water the temperature of which does not go above 85C.
Cook 30 to 35 minutes.
3. Cook two eggs in boiling water. Cook 12 to 15 minutes.
a. Cool one egg slowly, leaving it in the water in which it was cooked.
b. Cool the other egg rapidly, letting cold water from faucet run over it
until cold.
Compare with the eggs from 1 and 2 in texture and firmness of the white
and yolk. Which gives a tender and desirable product for eating? For slicing?
Do any have a green layer at the junction of the white and yolk?
Texture
Tenderness
Comments
White
Yolk
White
Yolk
Results and conclusions.
COOKING EGGS IN WATER 377
B. To determine the effect of cooking for varying lengths of time at a
high temperature upon the texture and consistency of egg white and yolk.
Cook in boiling water.
1. Cook 2 minutes.
2. Cook 3 minutes.
3. Cook 5 minutes.
4. Cook 7 minutes.
5. Cook 10 minutes.
Compare the consistency of the white and yolk cooked for varying lengths
of time. Compare with results obtained in A.
II. Out of the shell.
A. To determine the method of obtaining a desirable poached egg.
Use a pan deep enough so that water will entirely cover the egg. Add a pint
of water. Use more water if necessary, but all should use the same quantity.
A film of fat rubbed over the bottom of the pan before the water is added
seems to help prevent the egg from sticking to the pan. Have the water boiling
when the egg is added. Keep the water bubbling very slowly. (For edible
purposes it is better to keep the water below the boiling point after the egg is
added, but the temperature of the water in different pans may vary widely.
Hence, keeping the water boiling very slowly serves for comparative purposes.)
Cook 3 minutes. Start with fresh water for each experiment. Break the egg
into a sauce dish just before adding to the water. Slide it carefully into the
water. Study the structure of one egg after it is broken out of the shell. Note
the proportion of thick and thin white, for this will vary with different eggs.
If very different in some individual eggs, cook and repeat one part of the
experiment, to see if you get the same results the second time. Note the
chalazae. Do any spots appear on the yolk?
A. Fresh eggs.
1. Cook in plain water.
2. Add 24 teaspoon of salt per pint of water.
3. Add 1 teaspoon of vinegar per pint of water.
4. Decide which of the three experiments above gives the best-appearing
product, then repeat it; but swirl the water around the pan, dropping the egg
in the center.
B. Eggs deteriorated so that they have a larger proportion of thin white.
1. Repeat Al.
2. Repeat A2.
3. Repeat A3.
4. Repeat A4.
C. Repeat Al, using a ring placed in the bottom of the pan in which the egg
is placed. Or use any type of cup made for poaching eggs.
Which coagulates better, the thick or thin portions of the egg white? What
is the effect of adding salt? Vinegar? Would the technic in swirling the water
make any difference in the result? Why not swirl too hard? If eggs are
cooked at a lower temperature, should the time be increased?
Do you wish to try changing the proportion of salt? The time and tempera-
ture of cooking?
378
EGG COOKERY
White
Yolk
Comments
Extent of
coagulation
Texture
Extent of
coagulation
Texture
Conclusions.
Custards
Experiment 64.
To determine the factors that affect the coagulation and curdling of
custards.
Recipe :
Milk
Egg
Sugar
1 cup
1
2 tablespoons
244 grams
48 grams
25 grams
A. To determine the effect of rate of coagulation upon the texture and
consistency of custards.
1. Prepare 2 times the recipe, then divide into equal parts; use part one
for Al, and part two for A2. It is better for two or more students to
work together for this experiment. Combine all the ingredients and mix thor-
oughly. Put one part in the upper part of a double boiler. The boiler should
be rather deep to have the custard sufficient to cover the thermometer bulb
when portions of the custard are removed. A double boiler holding a quart
and about 4 inches in depth is satisfactory. Add a pint of cold water to the
lower part; then put the upper portion of the double boiler into the lower.
Make a record of the temperature of the custard mixture and the time. Put
over the fire and heat. The heating may be rapid until the custard mixture
reaches a temperature of 70C. Then the heat should be regulated so that at
least 1 to \ l /2 or more minutes will be required to elevate the temperature
1C., i.e., about 3 minutes should be required for the temperature of the
custard to go from 80 to 82. One student may hold the thermometer and
read the temperatures; a second can record the time and temperature. Record
the time every 5 during the first period of heating, i.e., 30, 35, etc. But
record the time for 1 rise after 78 is reached, i.e., at 78, 79, 80, 81,
etc. A third student may stir the custard and a fourth can remove portions
of the custard. It is easier to let the bulb of the thermometer touch the bot-
tom in the center of the double boiler. Use a wooden spoon for stirring.
Have dishes ready to put the custard in. Bend the bowl of an old metal spoon
until it is at right angles to the handle. Use it for removing portions of the
custard, taking out 2 tablespoons at each temperature. Remove portions of
the custard at 78, 80, 82, 84, 86, 88, and when curdled.
CUSTARDS
379
2. Repeat Al, but have the pint of water in the lower part of the double
boiler boiling when the upper part is added. Regulate the heat to keep the
water boiling very rapidly. Cook as quickly as possible, but not more than
6 minutes should be necessary. Record the temperature of the custard and
the time just before putting the custard over the boiling water. If possible,
record the temperature as under Al. The stirring should be rather rapid
for the cooking is rapid. It will also take rapid work to remove the custard
at the desired temperatures. Remove portions of the custard at temperatures
given under Al.
Note the temperature before and during curdling of the slowly and rapidly
cooked custards.
Does the temperature lag or drop in some instances? Prepare a time-
temperature chart, showing the period of time required for custard for
different groups and time intervals as follows. It will be found that the con-
sistency of a given custard at a definite temperature, say 80C., is directly
proportional to the time required to heat it from 76 to 80C. Compare
thickening of custard for different groups, noting time required for each
custard to reach a definite temperature. Also note curdling temperature and
highest temperature reached.
Time to reach
Time from
Time from
76C.
76 to 78
78 to 80, etc.
Min.
Min.
Min.
A. Group 1,
etc.
B. Group 1,
etc.
Compare the consistency of the custards at each temperature. What is the
effect of the rate of coagulation upon the amount coagulated at a definite
temperature? Would you advise the rapid or the slow cooking? Why? Com-
pare with baked custards heated to the corresponding temperatures.
B. Baked custards.
Prepare 2 times the recipe. Combine all the ingredients and mix thoroughly.
Divide into 5 portions, using equal parts in each cup. Put all the cups in a
large, flat pan. Set the pan in the oven. By supporting on an oven rack above
the custards insert a right-angled meat thermometer, so that the bulb of the
thermometer is at the center of one custard. Place a second thermometer
so that the temperature of the water can be read. Start heating the oven
and then pour boiling water around the custard cups until it comes as high
as the custard in the cups. If the oven has a regulator so that a low tempera-
ture, 125 to 150C. (250 to 300F.) is maintained, the custards can be
cooked without adding the water to the pan. Record the time and the tempera-
ture of the custard every 3 minutes if the oven has a glass door, otherwise
380
EGG COOKERY
every 5 minutes. Remove one custard of each series at the following tempera-
tures: 82, 83, 84, 85, and 87C.
C. To determine the effect of varying the proportion of ingredients in baked
custard.
Follow directions under B. If possible, bake all the custards under B and
C in the same pan. Prepare 2 times the recipe.
1. Use 1 egg, 1 cup of milk, 2 tablespoons of sugar, or use the custards
from B for a control.
2. Use 1 egg, 1 cup of milk.
3. Use 1 egg, 1 cup of milk, 4 tablespoons of sugar.
4. Use \]/2 eggs, 1 cup of milk, 2 tablespoons of sugar.
Are all the custards for the same experiment of the same thickness or
consistency? How might you account for this? Are the custards removed
at 83 C. all of the same consistency? Compare the time required for cook-
ing. Does the increased egg result in a thicker custard than when 1 egg is
used? Compare the stiffness of custards made with the whites and the yolks.
What is the effect of increasing the sugar? Which proportion of sugar is
desirable for serving? Are any of the custards curdled? What is the optimum
temperature for serving each custard?
Time of cooking
Consistency of custard at
To reach
80C.
From 80
to 87C.
82C.
83C.
84C.
85C.
87C.
Conclusions.
D. To determine the effect of substituting yolks or whites for the whole
egg-
Follow directions under B. Prepare 2 times the amount given below.
1. Use 2 yolks (36 grams), 1 cup of milk, 2 tablespoons of sugar.
2. Use 2 \vhites (60 grams), 1 cup of milk, 2 tablespoons of sugar.
Beat the whites only slightly before adding the milk. If beaten stiff they
float on top of the milk and do not blend well with it. Also fill the cups to the
same height as those containing the egg-yolk custard. Otherwise the larger
quantity of egg-white custard will heat more slowly than the egg-yolk custard.
When egg yolks are substituted for the whole egg in the custard, compare
the stiffness of the custards with those made from the whole egg cooked to the
same temperature. Compare the flavor. The color. Compare with custards
made of egg white.
E. To determine the factors that affect coagulation.
Prepare YZ the recipe, using only 1 custard cup.
1. Use 1 egg, 1 cup of distilled water, 2 tablespoons of sugar.
2. Use 1 egg, 1 cup of distilled water, 2 tablespoons of sugar. Dissolve l /3
teaspoon of calcium lactate in the distilled water before adding the egg and
sugar.
CUSTARDS
381
3. Use 1 egg, 1 cup of distilled water, 2 tablespoons of sugar. Bake until
the temperature at which D2 sets is reached. Remove from the oven and
add y$ teaspoon of calcium lactate that has been moistened in a tablespoon
of distilled water. Stir. What happens?
4. To 1 egg, 1 cup of distilled water, 2 tablespoons of sugar, add about 1/16
teaspoon or less of aluminum or ferric chloride. Mix the ferric or aluminum
chloride with the distilled water ; then add the beaten egg and the sugar. What
happens when the egg is stirred in the mixture? Continue stirring for a few
seconds.
5. Repeat El, but add Y$ teaspoon of aluminum or ferric chloride. Does the
custard coagulate during cooking? Test the custards with litmus paper.
6. To 1 egg, 1 cup of distilled water, and 2 tablespoons of sugar, add /4
teaspoon of salt.
7. Repeat E6, but omit the salt and add y$ teaspoon of a milk-salt mixture
used in feeding rats.
8. To 1 egg, 1 cup of distilled water, and 2 tablespoons of sugar, add ^
teaspoon of lemon juice.
9. To 1 egg, 1 cup of distilled water, and 2 tablespoons of sugar, add 1
teaspoon of lemon juice.
F. To determine the effect of beating on thickening power of the egg.
1. Use 2]/2 eggs. Beat in a bowl either by hand or with an electric mixer
until the yolks and whites are well blended. Weigh out 48 grams and combine
with 1 cup of milk and 2 tablespoons of sugar.
2. Beat the egg remaining from part Fl until thoroughly beaten. The egg
can be beaten as long a period as desired. Weigh 48 grams of the egg. Discard
the remaining egg. Combine the 48 grams with 1 cup of milk and 2 table-
spoons of sugar. If the egg was beaten with an electric mixer, put milk in the
mixer bowl and combine with the mixer. Does the egg tend to float on top
of the milk? Bake according to directions under B.
3. Beat 1 egg slightly, so that the yolk and white are not well blended. Add
to 1 cup of milk and 2 tablespoons of sugar.
What is the effect of increasing the egg upon temperature of coagulation?
Of varying the proportion of sugar? Does the distilled-water custard set?
What is the effect of adding calcium lactate? Salt? What is the reaction of
the custard containing the small proportion of aluminum or ferric chloride?
The one with the larger proportion? Does either set? Unless the proportion
of ferric or aluminum chloride is small enough, E4 may not set.
Time of
cooking
Coagulation
temperature
Texture
Flavor
Comments
Results and conclusions.
G. Soft custards.
The series under C and D may be repeated and cooked as soft custards,
or the baked custards may be omitted and the soft custards prepared instead.
Prepare once the recipe and follow directions under A for cooking.
382
EGG COOKERY
Salad Dressings
Experiment 65.
To determine the effect of acid upon coagulation of egg in cooked salad
dressings.
Recipe:
Egg yolks 4 72.0 grams
Sugar ^2 tablespoon 6.2 grams
Liquid total 1 cup 240.0 grams
Mustard $4 teaspoon
Salt % teaspoon
A. Cook in a double boiler. Follow directions under Experiment 64A for
cooking. It is not necessary to cook as slowly as under Experiment 64A,
but the time for each degree rise in temperature should be the same in all the
experiments.
Remove portions of the salad dressing at the following temperatures:
76, 78, 80, 82, 85, and 92C. Note the temperature when the salad
dressing coats the spoon.
1. Use l /s cup of vinegar, % cup of water.
2. Use y\ cup of vinegar, ^4 cup of water.
3. Use l /2 cup of vinegar, l /2 cup of water.
4. Use l /$ cup of lemon juice, % cup of water.
5. Use y\ cup of lemon juice, ^/\ cup of water.
6. Use y2 cup of lemon juice, y 2 cup of water.
7. Repeat Al, but add 1 tablespoon flour, 7 grams.
At which temperature is the most desirable texture for a salad dressing
obtained with the different proportions of acid? Which proportions of acid give
the thicker salad dressing? Does curdling occur at the higher temperatures?
From results with custard, what would be the result of increasing the propor-
tion of salt? Which produces the clearer salad dressing, vinegar or lemon
juice?
76
78
80
82
85
92
Conclusions.
B. To determine the effect of varying the ingredients and the proportion
of ingredients in salad dressings.
1. Repeat 65,2, or 65,5, but increase the salt to 1 teaspoon.
2. Repeat Bl, but increase the sugar to 2 tablespoons.
3. Repeat Bl, but substitute 72 grams of whole egg for the egg yolk.
4. Reduce the egg yolk to 36 grams and add 2 tablespoons (14 grams) of
flour.
OMELETS 383
Hollandaise Sauce
Experiment 66
To determine the factors affecting the smoothness of Hollandaise sauce.
Recipe :
Butter y cup 112 grams
Egg yolks 2 36 grams
Hot water y$ cup
Vinegar 1 tablespoon
Salt I /A, teaspoon
Paprika few grains
1. Melt the butter in the top part of a double boiler. When melted remove
from the heat and add the well-beaten egg yolks, stirring until blended with
the butter. Add other ingredients and return to the double boiler. Heat slowly
and stir continually. Remove samples at the following temperatures, 72, 74,
76, 78, and 80C. If mixture has not separated at 80C., continue to
remove samples until curdled.
2. Repeat 1, but do not beat the egg yolks before adding to the butter.
3. Repeat 1, but increase the egg yolks to 4.
4. Repeat 3, but omit the water and increase vinegar to 2 tablespoons.
5. Substitute lemon juice for any of the above. Compare smoothness and
consistency of the different sauces. Compare the flavor.
Omelets
Experiment 67.
To determine the factors that affect the texture of omelets.
Recipe :
Egg 1 Salt Y% teaspoon
Liquid 1 tablespoon 15 cc. Butter J/2 tablespoon 7 grams
Directions for mixing and baking.
The first omelets should not be used for comparisons for experiments. The
omelets should be made over several times if necessary to acquire the technic
and the manipulation necessary to make a good omelet.
Separate the white and the yolk of the egg. Beat the yolk until it will mix
well when folded in the white. Beat the white until it is frothy and add the
liquid; add the salt and continue beating until it is quite stiff. It should be
beaten until it will stay in an inverted bowl.
Mix the beaten white and yolk by folding. Use a spatula for folding. The
spatula should have a flexible blade near the end but should be rigid where
it joins the handle. Fold by holding the blade of the spatula parallel to the
right side of the bowl. Move to the bottom of the bowl, at the same time
pressing so that the spatula scrapes the material from the bottom of the
bowl. Bring up with the blade parallel to the left side of the bowl. As the
spatula is brought across the top of the material turn it upside down. Turn
384
EGG COOKERY
the bowl occasionally, and about every fifth stroke bring the spatula up
through the middle of the material for better mixing. Fold white and yolk
until well blended. They should not be mixed until a large portion of the
air is lost from the white, but they must be mixed enough to prevent separa-
tion of the white and yolk. Count the number of strokes used in mixing the
yolk and white. The number needed will vary with the size and kind of
utensil, usually about 20 to 25. The same number of strokes should be used
in mixing for all the experimental work and also the same size and kind
of utensils. If desired, different makes and styles of egg beaters and whisks can
be used. Count the motions required to beat the egg whites to the same degree
of stiffness. The butter is put in a frying pan or an omelet pan of the proper
size for a one-egg omelet. Melt the butter in the pan. Add the omelet and
cook over a medium flame for about ^2 minute before placing in the oven.
Have the temperature of the oven 160 to 165C. (320-330F.). Oven baking
is not necessary but it gives a uniform temperature for class work. Bake 25
minutes. If necessary, increase or decrease the time of baking. See Fig. 36,
p. 362.
A. To determine the effect of omitting the liquid and the effect of using
different liquids.
1. Omit the liquid in the recipe.
2. Use water for the liquid in the recipe.
3. Use milk for the liquid in the recipe.
4. Use tomato juice for the liquid in the recipe.
5. Use 1 teaspoon of lemon juice and 2 teaspoons of water for the liquid in
the recipe.
Which omelet gives the greatest volume? Which is the most tender? What
happens in 3 ?
No. of strokes
used for mixing
Volume
Texture
Tenderness
Flavor
Results and conclusions.
B. To determine the effect on the volume and the texture of omelets of
combining the liquid with the egg yolk.
Repeat the series under Al, but combine the liquid with the beaten yolk.
C. To determine the effect of cooking at different temperatures.
1. Repeat A2, and bake at 160C. (320F.).
2. Repeat A2, and bake at 140C. (285F.).
3. Repeat A2, and bake at 180C. (355F.).
Which cooking temperature gives the best results?
Results.
D. To determine the effect of beating the egg white to different stages of
stiffness on the texture and the volume of omelets.
1. Repeat A2, for a control.
2. Repeat A2, but beat the egg white until very dry and flaky.
MERINGUES 385
3. Repeat A2, but beat the white until it will flow if the bowl is inverted and
is not as stiff as for Dl.
Results,
Meringues
Experiment 68.
To determine some of the factors affecting the desirability and texture of
meringues.
Recipe:
Egg whites 2 60 grams
Sugar 4 tablespoons 50 grams
Water (may be omitted) 2 teaspoons
Salt >j6 teaspoon
Vanilla % teaspoon
Directions for mixing.
. Beat the egg white until foamy, 50 turns of handle of rotary beater. Add
the water, salt, vanilla, and beat an additional 100 turns with rotary beater.
Add sugar and beat 50 turns with rotary beater. (Note. The sugar may be
added gradually. If added in this manner, the amount of beating after addition
of salt should be shortened. Ask instructor for directions. Change or adapt
the extent of beating to suit the type of beater used, whether water is added,
and the consistency of the egg white.) The above quantity of meringue should
give enough for 4 pies about 6 inches in diameter. The meringues should be
between fy and \ l /2 inches in depth. Bake pastry. Fill shells with chocolate,
lemon, or butterscotch filling as desired. Spread the meringue carefully over
the filling to the edge of the crust, leaving it somewhat rough over the top.
The meringue may be placed on a hot or cold filling. However, if added to a
cold filling the time for baking will be longer, especially at the lower tempera-
tures. When possible keep portions of the pie over night to observe the extent
of leakage of the meringue.
A. Temperature of baking.
1. Bake at 230C. (446 or 450F. may be used) for 4 minutes.
2. Bake at 215C. (420 or 425F. may be used) for 6 minutes.
3. Bake at 200C. (392 or 400F. may be used) for 8 minutes.
4. Bake at 185C. (365F. or 375F. may be used) for 12 to 15 minutes.
5. Bake at 170C. (338F. or 350F. may be used) for 15 to 20 minutes.
6. Bake at 155C. (311F. or 300F. may be used) for 25 to 30 minutes.
B. Amount and kind of sugar.
Bake at temperature found best under A.
1. Use 1 tablespoon (12.5 grams) sugar per egg white.
2. Use 1^2 tablespoons (18.5 grams) sugar per egg white.
3. Use 2 tablespoons (25 grams) sugar per egg white.
4. Use 2 l /2 tablespoons (31 grams) sugar per egg white.
5. Repeat B3, substituting powdered sugar for the granulated sugar.
6. Use 1 tablespoon honey or sirup per egg white.
C. Extent of beating after sugar is added.
386 EGG COOKERY
Bake at temperature found best under A and use amount of sugar found
best under B.
1. Beat 25 turns of handle of rotary beater after sugar is added.
2. Beat 50 turns after sugar is added.
3. Beat 75 turns after sugar is added.
4. Beat 100 turns after sugar is added.
5. Fold in sugar with spatula, using 50 folds.
D. Time of adding sugar to egg white.
Bake at temperature found best under A and use amount of sugar found
best under B. Beat until foamy, add sugar and cook as indicated.
1. Add sugar and water (if used) at first and beat until shiny and stiff.
Beat 200 turns of beater handle. Remove Y of mixture for Dl.
2. Beat the mixture remaining from Dl 250 turns of the beater handle.
Remove /4 of original mixture for part 2.
3. Beat the meringue remaining from D2 300 turns. Use l /4 of the original
mixture for part 3.
4. Beat the remaining meringue 300 turns.
Repeat the above series. Beat egg white until foamy. Add water (if used)
and start adding sugar gradually. Beat until stiff.
E. Amount and kind of liquid.
Bake at temperature found best under A.
1. Do not add liquid to egg white.
2. Use 1 teaspoon of water for the full recipe.
3. Use 2 teaspoons of water for the full recipe.
4. Repeat E2 using lemon juice.
Angel Cakes
Experiment 69.
To determine the factors that affect the texture of angel cake.
Standard recipe:
Egg whites 1 cup 244 grams
Sugar \% cups 250 grams
Cake flour 1 cup 100 grams
Cream of tartar 1 teaspoon 3.6 grams
Salt y^ teaspoon
Directions for mixing and baking.
Bake 1/6 of the recipe for each experiment. Beat the egg whites until
frothy, then add cream of tartar and salt. Continue beating until they are the
desired stiffness. The peaks formed when the white follows the lifted beater
stand up fairly stiff and the tip end is slightly rounded. Sift the sugar to
remove lumps and large crystals so that it will dissolve readily when mixed
with the egg white. The sugar is sprinkled over the top of the egg and then
folded in with a spatula. See Experiment 67 for directions for folding. The
class should use spatulas of the same size. An egg beater can be used to fold
in the sugar, but if used all members of the class should use one, and the
number of strokes may need to be changed according to the size of the egg
ANGEL CAKES 387
beater. The flour is sifted to remove all lumps so that it folds in readily with
the mixed whites and sugar. If the sifter is a coarse one, sift the flour several
times. The flour is sifted over the eggs, then folded in. Flavoring is omitted
in the above recipe so that the flavor of ingredients is more distinct. When
used it may be added with the cream of tartar, thus preventing excess fold-
ing. To better compare the effect of other factors it is preferable to beat
the egg whites together and then divide after they are beaten. Pans 2^2 by 2^
by 5 inches will hold 1/6 of the above recipe. It is better to bake the whole
recipe in a pan with an opening in the center to facilitate baking, but small
portions bake well in a loaf. Let the baked cakes hang inverted in the pans
until cool.
A. To determine the amount of mixing of sugar to yield the best texture
and volume.
I. Standard method.
Beat enough whites at one time for the whole recipe. Add the cream of
tartar and salt. Divide into 6 parts, using 38 grams of the beaten white
for each 1/6 of the recipe. Bake at 175C. (347F.). There should be several
girls in this group. One girl should beat and weigh the egg whites. Each girl
should do the same manipulation on each cake. Thus if one girl folds the
first ^4 of the sugar, she should do this operation on each cake, but no more,
and pass it on to the next girl. Two girls can fold the flour, the first adding
3/5 and the other the remainder.
1. Add approximately % of the sugar, sprinkling it over the top of the beaten
egg. Fold 5 times with a spatula. Repeat for each % of the sugar. This
gives a total of 20 strokes for folding in all the sugar.
Sift approximately 1/5 of the flour over the egg and sugar mixture. Fold
with 5 strokes of spatula. Add another 1/5 of the flour and fold a total of 10
strokes with the spatula. Add 1/5 of the flour and fold a total of 15 strokes.
Add 1/5 of the flour and fold a total of 20 strokes. Add the last 1/5 of the
flour and fold a total of 40 strokes.
2. Repeat 1 but fold each *4 of the sugar 10 times with the spatula.
3. Repeat 1 but fold each ^ of the sugar 15 times with the spatula.
4. Repeat Al, but fold each % of the sugar 20 times.
5. Repeat Al, but fold each % of the sugar 30 times.
6. Repeat Al, but fold each *4 of the sugar 45 times with the spatula.
What is the effect on the size of the cells and cell walls when the sugar
is sufficiently mixed? When it is over-mixed? When it is insufficiently mixed?
Can the flour be blended well if the sugar has not been sufficiently mixed?
What is the effect on the texture and tenderness of longer mixing?
II. The meringue method.
Follow the same procedure as for Al, but do not beat the egg whites quite
so stiff. The peaks should be soft and the tip end should round over readily.
It may be necessary to decrease or increase each of the following parts by
5 or more strokes, depending on the stiffness to which the egg white is beaten.
If desired /4 f the sugar may be sifted with the flour. Follow directions
under AI,1 for folding the flour. Weigh out 38 grams of white for each part.
1. Add l /4 of the sugar to be beaten in the egg white. Beat the sugar into
the egg whites using 10 turns of handle of rotary beater or 10 strokes of
whisk for each ^ of the sugar.
388
EGG COOKERY
2. Repeat 1 but use 15 turns of rotary beater handle or 15 strokes of whisk
for each l /4 of the sugar.
3. Repeat 1 but use 20 turns of rotary beater handle or 20 strokes of whisk
for each l /\ of the sugar.
4. Repeat 1 but use 25 turns of rotary beater handle or 25 strokes of whisk
for each Y\ of the sugar.
5. Repeat 1 but use 30 turns of rotary beater handle or 30 strokes of whisk
for each Y\ of the sugar.
6. Repeat 1 but use 35 turns of rotary beater handle or 35 strokes for
each l /4 of the sugar.
Character
of crust
Volume
Crumb
Size of
cells
Size of
cell walls
Tender-
ness
Color
Moist-
ness
Flavor
Results and conclusions.
B. To determine the amount of mixing of flour to give the best angel cake.
Beat enough eggs at one time to make l /> of the full recipe. Add cream of
tartar and salt for Y* the full recipe. Divide the beaten egg white into three
parts using 38 grams for each part. Use either the standard or meringue
method of adding the sugar, with number of strokes found best under A.
Divide the work so that each girl does the same manipulation on each cake.
1. After adding the sugar, add the flour. Fold in with 40 strokes. Follow
directions for folding flour under AI,1.
2. Repeat Bl, but use 10 strokes to mix each 1/5 of the flour and a total
of 60 strokes.
3. Repeat Bl, but use 15 strokes to mix each 1/5 of the flour and a total
of 80 strokes.
What is the effect on the grain, the volume, and the tenderness of the
cake when the flour is mixed too long? Can less than 35 strokes be used?
C. To determine the effect of beating the egg whites to different stages
of stiffness on the texture of the angel cake.
Beat enough egg whites at one time to prepare Y 2 of the full recipe. Add
cream of tartar and salt for Y* the full recipe. The first portion is to deter-
mine the effect of too little beating of the white so that the egg white can
be weighed with as little beating as desired. Weigh out 38 grams of the beaten
white and use the remainder for 2 and 3. Divide the work so that each girl
does the same operation on each cake.
1. Add l /4 of the sugar. Add each l /4 of the sugar with the number of
strokes and method found best under A. Fold the flour with the number of
strokes found best under B.
2. Continue beating the egg white from Cl, until it is about the same stiff-
ness as that used under A and B. Weigh out 38 grams.
Add the sugar and the flour as in Cl.
ANGEL CAKES 389
3. Beat the remaining egg white from C2, until it is very stiff, dry, and
flaky. Weigh out 38 grams. Add the sugar and the flour as in Cl.
Would longer mixing of the egg white in Cl partially overcome the lack of
sufficient beating of the egg whites?
D. To determine the effect of varying the proportion of cream of tartar
used in angel cake, and the method of adding the cream of tartar.
1. Prepare 1/6 of the recipe for a control. Add the sugar by method and
number of strokes found best under A and the flour with the number of
strokes found best under B.
2. Repeat Dl, but omit the cream of tartar.
3. Repeat Dl, but increase the cream of tartar to 2 teaspoons for the full
recipe.
4. Repeat Dl, but omit adding the cream of tartar to the egg. Sift the flour
and the cream of tartar together 2 or 3 times, before adding the flour to
the egg and sugar mixture.
E. To determine the effect of increasing the proportion of sugar used in
the cake. (Formula II.)
1. Increase the sugar for the full recipe to \ l /2 cups. Beat enough egg
whites for ^ the full recipe. Add salt and cream of tartar for l /2 the full
recipe. Beat the egg whites by method and amount found best under A, but
leave them slightly under-beaten. Add the flour with number of strokes found
best under B.
2. Beat the remainder of the egg whites from El, the amount used in
other experiments. Weigh out 38 grams and repeat El.
3. Beat the remainder of the egg white from E2, until very dry and flaky.
Weigh out 42 grams. Repeat El.
When the sugar in the recipe is increased, should the egg white be beaten
longer to coagulate a larger proportion, thus giving greater rigidity to hold
the added sugar, or does over-beating lessen the rigidity of the egg white?
What would be the effect of increasing the mixing of the sugar and the egg
white? May the flour be increased to 107 grams when the sugar is increased
to \ l / 2 cups?
F. To determine the effect of reducing the proportion of flour in the stand-
ard recipe.
Reduce the flour for full recipe to 90 grams. Prepare 1/6 the recipe. Use
meringue or standard method or both for beating eggs, beating an amount to
give a desirable cake. Add flour as found best under B. If you think it advisable
repeat the experiment reducing the flour to 80 grams.
G. To determine the effect of different baking temperatures.
Prepare l /2 the full recipe following directions under F and using amount
of flour found most desirable. Divide the batter into 3 equal portions. Bake
one cake at 160C. (320F.), the second at 175C. (357F.), and the third
at 190C. (375F.).
H. Use formula III, p. 360. Use any or all methods that may yield a
palatable cake. Compare volume, texture and tenderness with cakes from the
standard recipe.
I. Repeat H, using formula IV, p. 360.
J. Repeat H, using formula V, p. 360.
390 EGG COOKERY
Sponge Cake
Experiment 70.
To determine the factors which influence the texture of sponge cakes.
Recipe:
Sugar 1 cup 200 grams
Pastry flour 1 cup 100 grams
Lemon juice 1 tablespoon 15 grams
Water 2 tablespoons 30 grams
Eggs 6 288 grams, yolks 108 grams, whites
180 grams
Lemon rind 1 tablespoon grated
Salt j/s teaspoon
A. Method of mixing.
1. Prepare 1/6 of the recipe. Bake at 160C. (320F.). Beat the egg yolk.
Add the sugar, the lemon juice, the grated lemon rind, the water, and the
salt. Beat until light, foamy, and lemon colored. Add the flour. Keep a record
of the number of strokes used for mixing the flour. Beat the egg whites until
they flow slowly when the bowl is partially inverted. Combine by folding the
beaten whites into the egg and flour mixture. Keep a record of the number of
strokes used for folding the egg whites in the flour mixture.
2. Beat the whole egg until light and foamy. Add the sugar gradually, then
the lemon juice, lemon rind, water, and salt. Beat until light. Sift a portion
of the flour over the top of the egg mixture and fold in. Continue until all the
flour is used. Keep a record of the number of strokes used in folding the flour.
3. Add the lemon juice, lemon rind, water, and salt to the sugar. Stir until
well mixed. Add the unbeaten egg yolk to the sugar and beat until light and
lemon colored. Add the flour. Keep a record of the number of strokes used in
mixing the flour. Beat the egg white until it flows slowly when the bowl is
partially inverted. Add to the flour mixture, keeping a record of the number
of strokes used for folding the egg whites.
4. Prepare l /2 of the recipe. Make a sirup of ]/2 cup of sugar and l /z cup
of water. Cook to 118C. and pour slowly over the beaten egg whites. Beat
the egg white while adding the sirup. Cool. Beat the egg yolks, adding the
lemon juice, lemon rind, and salt to the yolks. Fold the beaten yolks into
the egg white. Keep a record of the amount of folding used for the egg yolks.
Sift a portion of the flour over the egg mixture. Fold in. Continue adding
the flour until it is all folded into the egg mixture. Keep a record of the number
of strokes used for folding the flour. Omit the 2 tablespoons of water in
the recipe.
B. Variations in amount of mixing the flour and the egg white.
Repeat the series under A, but increase or decrease the number of strokes
used in folding the flour and the sugar so as to obtain the best texture in
the cake.
C. Vary the baking temperature.
CHAPTER XI
FLOUR AND BREAD
The composition of wheat may vary with several factors, such as varying
rainfall, temperature, and other climatic conditions, irrigation, texture and
composition of the soil, and the use of fertilizers. Bailey reviews all these
factors and others in "The Chemistry of Wheat Flour."
The kind of flour and to a great degree its composition depend upon
(1) the milling process, (2) the classes of wheat from which the flour is
milled, and (3) the purpose for which the flour is intended. Flour is also
made from rye, buckwheat, barley, corn, rice, potatoes, bananas, lima
beans, cottonseed, and soybeans, but the term flour refers to wheat flour
when no grain or product is mentioned.
The milling process and the structure of wheat. The wheat
kernel may be divided into three main parts: the bran, the germ, and the
endosperm, the relative proportion of each part of the entire kernel being
respectively about 14.5, 1.5, and 84 per cent. Milling is the process of
separation of the endosperm from the bran and germ. When no separation is
made, or all the flour streams are reunited, the flour is known as whole-
wheat flour, but otherwise the completeness of separation determines the
resulting grade of flour. If the separation is so complete that only the
heart of the endosperm is used, the resulting flour may be called a "fancy"
or "short" patent. In general, only about 72 to 75 per cent of the endo-
sperm is obtained in white flour, the remainder constituting bran and
shorts. Between the two extremes of flour, whole-wheat and fancy patent,
are many other varieties.
The steps in the milling process may include the following: cleaning,
tempering, breaking, sifting, or separating the primary products, purifying,
reducing, bolting, flour blending, and bleaching.
The structure of the wheat berry is shown in Fig. 42. Layer No. 1, some-
times called the bee's wings by millers, the hairs, and the dirt on the berry,
particularly that in the crease, are removed in the cleaning operations pre-
paratory to milling. Layers No. 2 to No. 6, shown in the surface drawing,
and the longitudinal and cross sections constitute the bran coats.
The gross appearance of a cross section of a wheat berry varies some-
what with the type of wheat and the ripening conditions. Hard wheats
are more flinty and vitreous than soft wheats. The proportion of gluten is
usually higher in hard than in soft wheats, and the gluten forms a con-
tinuous matrix in which the starch granules are imbedded. When the grain
contains a large proportion of gluten, the starch granules, as it dries out in
391
392
FLOUR AND BREAD
Ki-J-wsrS.,,, c-cntp^QT- 1 Q M
Courtesy of International Milling Company, Minneapolis
FIG. 42. The structure of a wheat kernel. The bran layers are shown peeled
back from the kernel. The portion from which the different flours are obtained
is shown in the longitudinal section.
THE MILLING PROCESS 393
ripening, are more firmly cemented to or held in the gluten matrix. In
milling the vitreous wheats naturally tend to yield coarser particles and less
free starch granules than soft wheats, unless the hard wheats are deliber-
ately ground fine. If the weather is hot and dry after flowering of the
wheat, a larger proportion of gluten and less starch are laid down in the
kernel. It is known that vitreous barley has smaller starch granules than
soft barley, and it is probable that this also applies to wheat.
In contrast to hard wheats, the soft wheats have air spaces throughout
the endosperm. The endosperm is quite friable and naturally breaks into
smaller particles in milling.
Tempering consists of adding a definite amount of water at a certain
temperature to wheat berries, the proportion of water added depending on
the moisture content of the wheat and other factors such as relative
plumpness and hardness of the kernels. In tempering wheat the water is
usually not left in contact with the wheat long enough for moisture to be
absorbed by the endosperm. Thus the pliableness and toughness of the bran
coats are increased so that they are more easily separated from the endo-
sperm. Sometimes, to prevent the endosperm from breaking into very fine
particles, the water is added in two portions, part of the first addition being
absorbed by the endosperm.
The germ because of its high fat content is easily flattened or flaked and
is removed by bolting from the other constituents of the wheat berry during
milling. The endosperm constitutes about 80 per cent of the wheat berry.
The starch is more concentrated in the immediate vicinity of the germ and
in the interior of the endosperm. The concentration becomes less and less
towards the outer layers of the wheat berry. The starchy endosperm being
drier and more friable tends to shatter more readily when the berries are
fractured or broken between rollers.
In the first breaks, the wheat kernels are mostly broken into large frag-
ments by the corrugated rollers. The coarser fragments, which are sepa-
rated from the finer ones by sifting, are returned to the next set of break
rolls of which there are 5 or 6. Other things being equal, a larger pro-
portion of fine particles is obtained from soft wheat than from hard wheat
during the first breaks.
Bolting or sifting, which occurs after each break, is the separation of
the coarse particles, which are reground, fine granules of flour, which are
not reground, and intermediate particles, which are sent to the purifier.
Purifying refers to a part of the milling process whereby particles pass
over a sloping, vibrating sieve. At the entrance the meshes of the sieve are
fine but gradually increase in size to the discharge end. As the particles
travel down this sieve they are separated according to size. During this
process controlled air currents lift out the flakier and more fibrous particles.
The remainder of the particles, known as purified middlings because they
are freer from branny, fibrous material, yield a more highly refined flour
after reduction.
394 FLOUR AND BREAD
The purified middlings are ground between smooth iron rollers to re-
duce them to the desired fineness. Since the flour bolted from the first
grinding of any stream of purified middlings is more highly refined, be-
cause it is freer of fiber than that produced by subsequent grinding of the
coarser residues, it is often used in making the so-called "short" patent
flours.
In separating the endosperm from the rest of the wheat berry and re-
ducing it to flour, some small bran particles are broken from the bran coats.
As these particles are formed they are separated from the flour stock and
may be graded according to size and included in the various feeds. As it is
impossible to prevent some flour particles' being removed with the bran,
these flour particles may also be graded according to size and may become
part of the feeds. The other portions into which the wheat berry may be
separated, in order as the percentage of bran particles increases, are First
Clear, Second Clear, Red Dog, Flour Middlings, Shorts, and Bran.
Classes of wheats used for flour. Wheats are classified in five main
groups as follows: (1) white, (2) hard red spring, (3) hard red winter,
(4) soft red winter, and (5) durum. Since the composition of the w r heat
varies with climatic and soil conditions to which it has been subjected in
growing, it is natural that many variations in composition occur Avithin
each class. The sections in which the different classes of wheat are grown
overlap to a greater or less degree. The major portion of the hard red
spring w T heat and durum wheat is grown in the North Central States of
the United States and in Canada, whereas hard red winter wheat is grown
chiefly in the South Central and Middle Central States. This class of
wheat leads all others grown in Iowa, Nebraska, Kansas, Oklahoma, Texas,
and Colorado. At present twice as much acreage is planted in hard red
winter wheat as in any other class of wheat. Soft red winter wheat is
grown in Missouri and the eastern half of the United States. It is also
grown in some Western States, particularly Oregon, Washington, and
Idaho. White wheat is grown to a limited extent in the northeastern part of
the United States and in Michigan, New York, and on the Pacific Coast.
Flour terminology. Flour terminology had become confusing but as
a result of the work of the committee on terminology of the Millers'
National Federation, in cooperation with the U. S. Department of Agri-
culture, definitions for labeling have been worked out and progress has
been made in clarifying the terminology. It has been suggested that grade
be used to refer to the type of flour as determined by the milling process,
whereas the word class be used to designate the kind of wheat from which
the flour is milled. According to such a plan, grades of flour would be
patent, clear, etc. ; classes would be durum, hard- and soft-wheat flours.
Definition of flour. The definition of flour is from the Definitions and
Standards for Food Products of the Service and Regulatory Announce-
ments of the U. S. Department of Agriculture, issue of 193 
