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AT

CORNELL UNIVERSITY

THE GIFT OF

Frances Phinney
In Memory of her Father

Mervin Phinney
(CALS student in 1912)

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ALISUAAINN TIANYOD
LV FINLINIAV AO ADATION ALVIS MUOA MAN ‘AMOLVAOAVI ONILSAL MOODAVE

A DAIRY
LABORATORY
GUIDE

By
H. E. ROSS

Assistant Professor of Dairy Industry
New York State College of Agriculture at Cornell University

NEW YORK
ORANGE JUDD COMPANY

IgI2

Copyright, 1910, by
ORANGE JUDD COMPANY
All Rights Reserved

Printed in the U. S. A.

PREFACE

In the study of any science the student should,
so far as possible, work out his own problems. Yet
the beginner may be saved much useless time and
labor by helpful suggestions at the proper time.
This Manual is designed as a guide to students in
dairy laboratory work, with just enough explana-
tion given to supplement the exercises which are
outlined in the Manual. It is not intended for a
text book and should not be used in the place of
one.

The author’s thanks are due Prof. W. A. Stock-
ing, Jr., for many helpful suggestions in the ar-
rangement and preparation of this book.

The author recognizes that a book of this kind
needs frequent revision, and an effort will be made
to keep this Manual up to date.

H. E. Ross.
Dairy Laboratories,

New York State College of Agriculture,
at Cornell Uutversity.

August 31, 1910.

hii

TABLE OF CONTENTS

I
The Composition of Milk......... 0.0... e000.

II
Explanation. The Babcock Test........... one

III
Explanation of Boiled Milk Test and Formalde-
hyde Test cacssset seated sna aeueenes

IV

Explanation. Mixing Samples of Butter Be-
fore Testing for Fat and Moisture.......

Vv
Explanation. The C. U. Butter Moisture Test

VI
Explanation. The Specific Gravity of Milk and
the Lactometer: ...6.0ss0cssneeeeceacw wn
VII

Explanation. The Board of Health Lactometer
v

18

19

23

27

37

vi DAIRY LABORATORY GUIDE

VIll
Explanation. Use of the Hand Machine in
Babcock: Rést wsseaieie te cede tira oe eae dies 38.
IX
Explanation. The Acidity of Milk........... 43
, x
Explanation. The Effect of Speed of Machine
on the Babcock Test...............0000e SI
XI

Explanation. Commercial Rennet andIts Use. 69

A Dairy Laboratory Guide

THE COMPOSITION OF MILK

Milk is composed of a great many substances,
but, so far as the dairyman is concerned, there are:
only six constituents which are of prime impor-
tance. The following table gives the constituents
of milk, together with the per cent of each, ob-
tained by a large number of analyses:

Water sco acier ates 87.0 per cent
AE sors) peataeauetaensotys 4.0 per cent
Casein -saaaace% ae as 2.6 per cent
SUGAR caaewos eens 5.0 per cent
Albumen ......... 0.7 per cent
ASH si hed asst alee ta 0.7 per cent

Although in the above table the different con-
stituents are given definite per cents, yet the com-
position of normal milk is very variable. The
water needs no discussion, as it is just like the water
found anywhere else in nature.

Fat is present in milk in the form of minute drop-
lets or globules. These globules are distributed
throughout the milk and are not in solution, but
in fine suspension. This state is called an emulsion.
It was disputed for a long time as to whether or not
the fat globule had a membrane around it. It is
now believed by the best authorities that the fat
globule has no membrane, but that the droplet

2 A DAIRY LABORATORY GUIDE

keeps its circular form because of its power of con-
densing upon its surface the serum of the milk.
The size of the fat globules differ in milk from
different breeds of cows, and it is supposed that the
larger the fat globules the more easily they rise to
the surface when the milk is left standing in a
vessel.

Butter is composed largely of fat, so we speak of
the fat of milk as butter fat.

Fat is the most important constituent of the
milk, because milk which contains a fair amount of
butter fat is more valuable as a food than a milk
which is poor in fat. The other food constituents
of the milk usually increase or decrease as the fat
increases or decreases. This is true, however, only
within certain limits.

Fat is an important constituent of nearly all of
the products of milk, so that in most cases a milk
rich in fat is more valuable for manufacturing pur-
poses than a milk poor in fat.

On account of the importance of the fat, it is
made oftentimes a basis of payment for milk.

Butter fat is composed mainly of nine different
fats. There are a few fats which are present in
such minute quantities that they are of no prac-
tical importance. All of the fats have the same
basis, namely, glycerin, and the fat is made by the
chemical union of glycerin and the corresponding
fatty acid. For example, the fat butyrin is made
of glycerin and butyric acid. The fat stearin is
made of stearic acid and glycerin. While the com-
position of the different butter fats are known, yet
the chemist is unable to make them in the labora-
tory.

The fats of butter fat are divided into two main
groups, the volatile and nonvolatile, and are so

A DAIRY LABORATORY GUIDE 3

named because they are made respectively from
volatile and nonvolatile fatty acids.
The fats under each class are as follows:

VOLATILE NONVOLATILE
Butyrin Olein
Caprin Myristin
Caproin Palmatin
Caprillin Stearin
Laurin

There is some dispute as to whether laurin is a
volatile or nonvolatile fat, but it is usually consid-
ered volatile. The volatile fats compose about 8
per cent and the nonvolatile about 92 per cent of
butter fat. The fats of butter fat have different
characteristics and properties, and one chief dif-
ference of fats is their melting point. For example
the melting point of stearin is about 143° F., and
the melting point of olein is about 40° F. A varia-
tion in the amount of either of these two fats would
necessarily cause the melting point of butter fat to
vary. The melting point of butter fat is usually
between 92° F. and 96° F.

Casein is the chief proteid compound of milk, and
forms about 20 per cent to 23 per cent of the milk
solids. It exists in milk in very fine suspension,
and is held in suspension by the salts of calcium.
It is, therefore, sometimes called calcium casein.
The casein is in such a fine state of suspension that
it cannot be filtered out of the milk by any ordinary
means. This fine state of suspension is called the
collodial state. When milk sours naturally and
enough acid is found to unite with the lime salts
of the milk, the casein is precipitated. Casein is
also precipitated by any acid and rennet or pepsin.
Casein is valuable as food both in raw milk and in

4 A DAIRY LABORATORY GUIDE

the products of milk, such as the various kinds of
cheese. It is also used commercially in many
ways, some of them being as a substitute for -cel-
luloid in the manufacture of buttons and _ toilet
articles. It is also used in cold water paints. By
a new process it is said that casein is now being
made into a substitute for ivory, making excellent
table tops, mantels, etc.

Sugar forms about 37 per cent to 39 per cent of
the milk solids. The chief value of milk sugar is
its food value in milk. It is also used in pharmacy
in mixing powders, coating pills, etc. Milk sugar
is not used very extensively commercially because
of the expensive cost of manufacture. It is not
as sweet as cane sugar, because it is not as soluble.
It has the same chemical formula (C,92H220j41)
as cane sugar. Acid is produced naturally in milk
by the action of bacteria upon the milk sugar.

The albumen in milk is in solution. It is valu-
able chiefly as a food in milk. It has one commer-
cial use in the manufacture of Italian cheese. This
cheese is made where large quantities of whey are
produced. The whey is heated nearly to the boil-
ing point, and this heat precipitates the albumen.
The whey is then drawn off and the albumen is
dipped into molds. The cheese made from albumen
forms a very good, nutritious food.

The ash is the part of milk left after burning, and
it is the most constant constituent of the milk.
It very rarely goes below .68 per cent or above .72
per cent. It consists chiefly of the phosphates of
calcium and the chlorides of sodium, potassium,
iron and magnesia. :

Ash is important as a food in furnishing the
mineral constituents for the body.

A DAIRY LABORATORY GUIDE 5
THE BABCOCK TEST

The Babcock test is a test for the per cent of fat
in milk and its products. It was invented by Dr.
S. M. Babcock, chief chemist for the experiment sta-
tion at Wisconsin, and a description of the test was
published in a report of 1890 from that station.
The instrument used to measure the milk is called
a pipette and holds up to its graduated mark 17.6
cc. Since milk is somewhat viscous, the pipette
will deliver on an average 17.44 cc., which is for
all practical purposes 18 grams. In using the
pipette the milk is drawn above the 17.6 cc. mark
and the soft part of the index finger placed quickly
over the pipette. The column of milk can be
easily controlled and allowed to flow out until it is
on a level with the 17.6 cc. mark. The pipette
should always be held so that the 17.6 cc. mark is
on a level with the eye. The sample to be tested
is measured into a special bottle with a graduated
neck, holding a column of melted fat which is a
definite per cent by weight of the 18 grams of milk
taken. In adding the milk to the bottle the latter
should be held in a slanting position, so that the
milk will run down the lower inside of the bottle
neck and will not be forced out by the outcoming
air.

After measuring the milk into the bottle, 17.5
cc. of sulphuric acid (H2SOx4) of a specific gravity
of 1.82 to 1.83 is added and the milk and acid at
once thoroughly mixed. The acid burns up (by
moist combustion) everything in the milk except-
ing the fat. The same precautions should be ob-
served in adding the acid as in adding the milk,
namely, to slant the bottle, and the bottle should be
revolved as the acid is poured in, so that all of

4 A DAIRY LABORATORY GUIDE

the products of milk, such as the various kinds of
cheese. It is also used commercially in many
ways, some of them being as a substitute for cel-
luloid in the manufacture of buttons and _ toilet
articles. It is also used in cold water paints. By
a new process it is said that casein is now being
made into a substitute for ivory, making excellent
table tops, mantels, etc.

Sugar forms about 37 per cent to 39 per cent of
the milk solids. The chief value of milk sugar is
its food value in milk. It is also used in pharmacy
in mixing powders, coating pills, etc. Milk sugar
is not used very extensively commercially because
of the expensive cost of manufacture. It is not
as sweet as cane sugar, because it is not as soluble.
It has the same chemical formula (Cy2H22041)
as cane sugar. Acid is produced naturally in milk
by the action of bacteria upon the milk sugar.

The albumen in milk is in solution. It is valu-
able chiefly as a food in milk. It has one commer-
cial use in the manufacture of Italian cheese. This
cheese is made where large quantities of whey are
produced. The whey is heated nearly to the boil-
ing point, and this heat precipitates the albumen.
The whey is then drawn off and the albumen is
dipped into molds. The cheese made from albumen
forms a very good, nutritious food.

The ash is the part of milk left after burning, and
it is the most constant constituent of the milk.
It very rarely goes below .68 per cent or above .72
per cent. It consists chiefly of the phosphates of
calcium and the chlorides of sodium, potassium,
iron and magnesia. :

Ash is important as a food in furnishing the
mineral constituents for the body.

A DAIRY LABORATORY GUIDE 5
THE BABCOCK TEST

The Babcock test is a test for the per cent of fat
in milk and its products. It was invented by Dr.
S. M. Babcock, chief chemist for the experiment sta-
tion at Wisconsin, and a description of the test was
published in a report of 1890 from that station.
The instrument used to measure the milk is called
a pipette and holds up to its graduated mark 17.6
cc. Since milk is somewhat viscous, the pipette
will deliver on an average 17.44 cc., which is for
all practical purposes 18 grams. In using the
pipette the milk is drawn above the 17.6 cc. mark
and the soft part of the index finger placed quickly
over the pipette. The column of milk can be
easily controlled and allowed to flow out until it is
on a level with the 17.6 cc. mark. The pipette
should always be held so that the 17.6 cc. mark is
on a level with the eye. The sample to be tested
is measured into a special bottle with a graduated
neck, holding a column of melted fat which is a
definite per cent by weight of the 18 grams of milk
taken. In adding the milk to the bottle the latter
should be held in a slanting position, so that the
milk will run down the lower inside of the bottle
neck and will not be forced out by the outcoming
air.

After measuring the milk into the bottle, 17.5
ce. of sulphuric acid (HgSO4) of a specific gravity
of 1.82 to 1.83 is added and the milk and acid at
once thoroughly mixed. The acid burns up (by
moist combustion) everything in the milk except-
ing the fat. The same precautions should be ob-
served in adding the acid as in adding the milk,
namely, to slant the bottle, and the bottle should be
revolved as the acid is poured in, so that all of

6 A DAIRY LABORATORY GUIDE

the milk adhering to the neck of the bottle
will be washed down. The vessel contain-
ing the acid should be kept corked in order
to prevent the acid taking up moisture from the air
and becoming too weak for use. If the acid is too
weak more than 17.5 cc. are used, and if too strong
less than 17.5 cc. are used. Good acid is colorless,
although it may be quite dark and at the same time
be useful for the Babcock test. It must, in any
case, be free from undissolved foreign particles.

After adding the acid to the milk the bottles are
placed in a centrifugal machine and whirled. Care
should be taken to have the machine balanced, i. ¢.,
for every bottle on one.side of the machine there
should be a corresponding bottle on the opposite
side of the machine. The bottles are centrifuged
for five minutes and then filled with hot water up
to the base of the neck. Centrifuging is then con-
tinued for two minutes more and hot water is added
to bring the fat into the graduated neck. The cen-
trifuge is then run for one minute.

The bottles are then ready to read, and in case
of whole milk one should read between the extreme
points of the fat column. This method of reading,
by comparison with the chemical method, has been
found to make up for the fat which remains in
the bottom of the bottle and cannot be removed by
centrifuging. The bottles should be read at a tem-
perature of 120° F, It is no trouble to obtain this
temperature if centrifuging has been done with a
steam machine. Where the machine is filled with
steam the bottles should stand for from thirty
seconds to one minute in a room at ordinary tem-
perature to allow excess of heat to pass off before
reading. Ifa hand machine is used the tester must
have hot water placed in it to obtain the required

A DAIRY LABORATORY GUIDE VA

temperature. This is especially necessary if the
testing is being done in a cold room.

The machine should always be kept well oiled
and securely fastened to the support on which it is
being operated. Skimmed milk contains such a
small amount of fat that the fat column could not be
read in an ordinary whole milk bottle. A bottle is,
therefore, used which has a neck with a small bore.
This neck is so small that the milk and acid could
not be poured through it, so a funnel tube is pro-
vided for this purpose. The skimmed milk bottle
should be placed in the machine in such a position
that the funnel tube will be on the outside. This
will prevent fat lodging in the space between the
tube and the wall of the bottle.

The sulphuric acid is added to the milk to
destroy all of the milk solids except the fat, and the
chief solid to be destroyed is the casein. Skimmed
milk contains proportionately more casein than
does whole milk and, therefore, in making a Bab-
cock test of skimmed milk 2 cc. extra of sulphuric
acid should be used. The fat globules in skimmed
milk are small in size and correspondingly hard to
remove. A Babcock sample of skimmed milk
should, therefore, be whirled ten minutes, two
minutes and one minute.

Cream is so viscous that it cannot be measured
accurately into a test bottle by means of a pipette
It should always be weighed. The New York state
dairy laws now consider it a misdemeanor to meas-
ure cream for testing where the tests are used as 3
basis of payment for butter fat.

Because the cream is sometimes too rich in butter
fat to be tested in an ordinary cream bottle, y
grams are tested in place of 18 grams and the result
multiplied by two. Nine-gram cream bottles are

8 A DAIRY LABORATORY GUIDE

also coming into common use. These bottles give
the reading direct without any computation. In
testing 9 grams one would naturally use one-half
the usual amount of sulphuric acid. On account,
however, of the large proportion of fat present, the
acid is liable to char the fat; and for this reason it
is better to add approximately 9 grams of water
and then add a little less than the usual amount of
acid.

Butter is tested in the cream bottles, from 3 to 4
grams being used for the test. Enough warm
water is added to bring the sample up to approx-
imately 18 grams, and from Io to 12 cc. of the sul-
phuric acid are used.

Cheese is also tested in the cream bottle, 4 to 5.
grams being used. The cheese must first be minced
with a knife as fine as possible in order to make it
possible for the acid to dissolve all of the casein.
After the cheese is weighed into the bottle, about
5 cc. of hot water are added and the mixture shaken
vigorously for two or three minutes. This softens
the casein. Enough hot water is then added to
bring the sample to approximately 18 grams. The
sample is again shaken for two or three minutes,
and the ordinary amount of H2SO, is then added.
If the cheese is old and dry, 2 or 3 cc. of HeSOxz in
excess of the usual amount are sometimes necessary
to dissolve the casein. In mincing the cheese the
sample should not be allowed to dry out any more
than is absolutely necessary.

In the cases of both the butter and the cheese,
the results obtained must be reduced to an 18-gram
basis, because the bottles are graduated for that
amount. This can be done by dividing the per cent
obtained by the number of grams used and multiply
the quotient by 18. e

A DAIRY LABORATORY GUIDE 9

Whey is usually tested in whole milk bottles,
although it is best to test it in skimmed milk bot-
tles when possible. The right bottle to use can
only be determined by actual experiment. Whey
requires less acid than whole milk, usually about
12 cc.

EXERCISES

12

A DAIRY LABORATORY GUIDE

EXERCISE I
THE BABCOCK TEST

Draw the milk above the mark on the pipette
and allow the milk to settle just to the mark.

Repeat this until some proficiency in the use of
the pipette is obtained.

What two special precautions are to be observed
in handling the pipette?

Test by the Babcock method a sample of whole
milk. Perform this test before doing either
3 or 4.

Measure out into your white cup 50 cc. of the
same sample of milk used in experiment 2.
Add to this 15 cc. of water. Mix thoroughly
and test in duplicate by the Babcock method.

Using milk from the same sample as used in
experiment 2, measure out 50 cc. of milk and
add to it 15 cc. of skimmed milk. Mix thor-
oughly and test in duplicate by the Babcock
method.

Did you obtain the most fat in experiment 3 or
experiment 4? Include in your notes a brief
description of the Babcock test.

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

13

14

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE I5

EXERCISE II
BABCOCK TEST

Test in duplicate a sample of whole milk, skimmed
milk and cream. Test the skimmed milk in
the same way that the whole milk is tested.

Why is cream taken by weight instead of by
volume?

Why are 9 grams used instead of 18 grams?

When 9 grams of cream are tested in an 18-
gram bottle, what correction has to be made
in the result and why?

Retest the cream and skimmed milk. Add acid
to the skimmed milk about one-fourth of an
inch above the mark and whirl ten minutes
the first time, two minutes the second time
and one minute the third time.

In retesting the cream do not add water, and
use one-half the usual amount of acid.

In order to save time the cream and skimmed
milk may be whirled together.

Explain fully the object of using extra acid and
whirling an extra length of time in testing
skimmed milk.

Record carefully any difference in the appear-
ance of the fat column of the cream in ex-
periments 1 and 2.

What should be the appearance of an ideal fat
column in a completed Babcock test?

16

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

17

18 A DAIRY LABORATORY GUIDE

EXPLANATION OF BOILED MILK TEST
AND FORMALDEHYDE TEST

There are two principal tests for boiled milk.
One test makes use of three chemicals—hydrogen
peroxide, potassium iodide and starch. In the
second test two reagents are employed—hydrogen
peroxide and paraphenylenediaminehydrochloride.
In both cases a blue color results if the milk has
not been boiled. If the milk has been boiled no
blue color will result. The last named test acts
more rapidly than the first one and also gives a
more intense color. Any double oxide may be sub-
stituted in place of the hydrogen peroxide. Such a
double oxide would be calcium peroxide. There is
in milk an enzyme galactase which is destroyed by
heat. When the milk has not been heated this
enzyme sets free the oxygen from the oxidizing
agent, and in case of the first test, the free oxygen
splits up the potassium iodide and liberates free
iodine. The starch in the presence of free iodine
turns blue. In case of the second test the oxygen
liberated by the galactase acts directly on the
paraphenylenediaminehydrochloride and turns the
solution blue. Hydrogen peroxide often contains
sulphuric acid. When this is the case, the reagent
is useless for the test with starch, as the free acid
would break up the potassium iodide. If this hap-
pened a blue color would result whether the milk
had been heated or not.

The test for formaldehyde is a delicate one and
is easy to perform, inasmuch as it may be done in
cofinection with the Babcock test. The regular
amount of milk is measured with the 17.6 cc. pipette
into a Babcock test bottle and a few drops of ferric
chloride added. The regular amount of sulphuric

A DAIRY LABORATORY GUIDE 19

acid is next added, and if formaldehyde is present
a lavender-colored ring will appear between the
layer of acid and the layer of milk. If the contents
of the bottle are slowly mixed the dissolving casein
will take on a lavender color. The test will not
work if the milk is too old or if too much of the
formaldehyde has been added to the milk.

Sometimes sulphuric acid contains ferric salts as
an impurity; and when such is the case, the acid
will give the test for formaldehyde without the use
of ferric chloride. It is best however, to always
add the ferric chloride to make sure there is a ferric
salt present.

EXPLANATION. MIXING SAMPLES OF
BUTTER BEFORE TESTING FOR FAT
OR MOISTURE

Before testing a sample of butter for either
moisture or fat the sample should be thoroughly
mixed. Fat and water do not readily mix, and
special precautions must be taken to make the
sample uniform throughout. The butter should be
heated and stirred until it is about the consistency
of thick cream. Do not heat the butter too much,
as the water and fat will entirely separate and it is
difficult to remix them again. The sample should
then be cooled and stirred thoroughly while
cooling, else the fat will cool rapidly on the
outside and force all of the water towards
the middle of the sample. The cooling process
should be kept up until the sample is quite firm.
The heating and cooling may be accomplished by
placing the butter in any convenient vessel, such
as a glass-stoppered sample jar. The jar may then
be held under a water faucet or set in a dish of
water.

20

Ts

2.

A DAIRY LABORATORY GUIDE

EXERCISE III
BABCOCK TEST

Test by the Babcock method a sample of whole

milk, skimmed milk and butter.

Mix the butter properly before weighing it out

for the test.

Measure out about 36 grams of skimmed milk

(Babcock pipette twice full to the mark).
Divide approximately into four parts. Test
two of these parts for boiling by two dif-
ferent methods. Boil the remaining 18
grams, divide approximately into two parts
and test for boiling by two different methods.
Give the chemicals used in each case. Do
not add the chemicals to the milk while the
milk is hot.

Measure out in duplicate a sample of skimmea

milk as for the Babcock test. Before adding
the sulphuric acid dip your stirring rod into
the formaldehyde and rinse it off in one of
the samples. Then add to both samples the
ferric chloride and sulphuric acid and note
the difference in color due to formaldehyde.

Test any four of the samples furnished, for

formaldehyde. Report by number.

Sometimes sulphuric acid will alone give the

color test for formaldehyde. Why is this?

Why fs it best to always add the ferric chloride

when making the formaldehyde test?

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

21

22

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE 23

THE C. U. BUTTER MOISTURE TEST

When butter is heated over a flame, the casein
forms a snow-white blanket over the surface of the
butter. By a comparison with the chemical method
it has been found that when the butter loses its
snow-white color and turns a dirty brown color the
sample has given up its moisture. When this
brown color has appeared it is time to remove the
sample from the flame. Heating butter in a direct
flame is liable to volatilize some of the butter, even
before all of the water has been given off. In order
to do away with this danger a sheet of asbestos is
placed between the flame and the container of the
sample. The asbestos so tempers the flame that
while a high heat is produced, the danger of sud-
denly volatilizing the butter is largely done away
with.

The scales used are made especially for use in
butter-moisture work. They are so constructed
that after the moisture is driven off, each notch
the large weight is reversed equals 1 per cent of
moisture driven off, and each notch that the small
weight is reversed equals .1 per cent of moisture
driven off. Always allow the sample to cool be-
fore weighing. While the sample is cooling it is
well to cover it with something (a sheet of paper
will do), so that the sample will not take water
from the air.

24

A DAIRY LABORATORY GUIDE

EXERCISE IV

BABCOCK TEST AND BUTTER MOISTURE

TEST

Prepare a sample of butter for the moisture test
and test by the C. U. method.

Test a sample of milk in the ordinary way.

Retest the same sample in duplicate, using only
9 grams of the sample. (It must be weighed
out.) Make the sample up to 18 grams by
adding water. Add the usual amount of
acid.

Test a sample of cream in the ordinary way.

Retest the cream in the whole milk bottle, divid-
ing 18 grams between four bottles (4%
grams by weight in each bottle).

In each case add enough water to bring the
sample up to 18 grams and then add the
proper amount of acid as indicated by the
appearance of the sample. Add the acid
slowly, a little at a time, and shake thor-
oughly.

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

25

26

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE 27

THE SPECIFIC GRAVITY OF MILK AND
THE LACTOMETER

The specific gravity or density of a substance is
a ratio between the weight of a given volume of
the substance and the weight of a given volume of
some other substance taken as a standard. The
standard for liquids is water and its specific gravity
istakenasone. Milk is slightly heavier than water,
and the specific gravity of normal milk averages
1.032, and the specific varies from 1.029 to 1.035.
If we add water to milk the specific gravity is
lowered, because water is lighter than milk; and if
we skim milk we take away fat which is lighter
than milk and the specific gravity is increased.
When the water is added to milk the effect is the
same as it would be if the solids were actually re-
moved from the milk. This is true because the
solids which were distributed throughout a given
volume on the addition of water, have to
distribute themselves throughout the increased
volume of the liquid. For this reason we say
that the addition of water to milk “ decreases”
the total solids, and it is a fact that when water is
added to milk all of the solids are decreased in the
same proportion. It is important to remember
this fact when one is figuring out the per cent of
adulteration of milk.

THe LacTomeTer.—The instrument used to
measure the specific gravity of a liquid is called a
hydrometer, and there are many kinds of specialized
hydrometers. The hydrometer used to test the
density of milk is called a lactometer, and, for the
most part, only two kinds are used. One of these
is called the Quevenne (called Q. for abbreviation)
and the other is called the New York State Board of

28 A DAIRY LABORATORY GUIDE

Health (commonly called the B. of H. lactometer).

The Quevenne lactometer has a long, narrow
stem which is extended into a hollow glass tube of
much larger diameter than the stem itself. At the
lower end of the instrument is a bulb of mercury
which causes the lactometer to sink in the liquid
to its proper level. The upper part of the stem
contains a thermometer scale, as it is important to
know the temperature of the milk when the lac-
tometer reading is taken. This scale does not re-
cord high temperature, and, therefore, the instru-
ment should never be placed in hot liquids. In
order to clean the lactometer wash in cool water
and wipe with a dry cloth. Immediately below the
thermometer scale is a lactometer scale with num-
bers ranging from 15 to 45, the lowest readings
being at the upper end of the scale. One may ob-
tain the specific gravity reading by prefixing I.0
before the lactometer reading. Thus, if the in-
strument gives a reading of 33, the specific gravity
would be 1.033. The fact that the Quevenne lac-
tometer gives specific gravity readings directly is
one of its chief advantages.

Temperature affects the density of liquids. The
colder the milk the more dense it is, and the warmer
the milk the less dense it is. For this reason lac-
tometers are standardized to give readings at a
temperature of 60° F. When milk is warmer or
colder than 60° F. a correction must be made, and
this correction for the Quevenne is .1 of a lactometer
degree for every degree in temperature that the
sample is above or below the standard temperature.
When we cool the milk down we add; when we
warm the milk we subtract. For example, if a
lactometer gave a reading of 32 at a temperature
of 66° F., we would add .6 (.1X6) to the lactometer

A DAIRY LABORATORY GUIDE 29

reading, making the corrected or true reading 32.6.
In this case the specific gravity would be 1.0326.

Familiarity with the action of the lactometer may
be obtained by working theoretical problems, of
which the following is an illustration: If the
lactometer reading of a sample of milk is 31.5 at
62° F., what would be the reading at 57° F.? In
this case 57° F. becomes our standard, because it is
the temperature to which we are going to lower the
sample. Since the sample is 5 degrees too warm,
5 (.1X5) of a lactometer degree must be added to
the lactometer reading, making the true or cor-
rected lactometer reading 32.

When used in connection with the Babcock test the
lactometer reading is important in obtaining the total
solids and solids not fat of milk. There are several
of these formule in use, and while they do not give
quite as accurate results as the chemical method,
they give results which are accurate enough for all
practical purposes. They are as follows:

1. &Et—S. N. F. Babcock’s formule.
2. HES. N. F. Troy’s formule.
y% L+.2f+.14—S. N. F. Babcock’s modi-
fied formula.

Generally speaking, the first formula gives the
highest results, the second next highest and the
third the lowest results. One can find the total
solids by adding the fat reading to the solids not
fat. In these formule L stands for the lactometer
reading and F for the fat reading.

In using these formule, the following precaytions
must be especially noted: Board of health readings
can never be used in these formule, consequently
B. of H. readings must be changed to Q.; specific
gravity readings cannot be used; the per cent of
fat expressed in hundredths cannot be used.

30 A DAIRY LABORATORY GUIDE

An illustrative example will show how these
formule operate. Suppose the Q. lactometer read-
ing of a sample of milk was 32.5 at 60° F. and the
fat reading was 4.2 per cent, what are the solids
not fat?

Formula=

q TERMS. N. F. .7X4.2=2.94
2.94-132.5=35-44
35-44-+3.8=9.32+-

Formulating the above calculation:
#254294 9.32% S. N. F.
9.32-+4.2=13.52 total solids.

Using formula 2:
iF —S, N, F.
32.5-+4.2=36.7
36.7--4=9.17+% S.N. F.

Formulating the above calculation:
2544? —o.17 SN. F.
9.17+4.2==13.37 T. S.

Using formula 3:
Y%L+.2f+.14=S. N. F.
32.5--4=8.12
2X 4.2.84
8.12+.84+.14=9.10 S. N. F.
9.10+4.2=13.30 T. S.

By modifying Babcock’s third formula the total
solids may be obtained directly. It is as follows:

yy L+1.2i+.14=T. S.

Using the above lactometer and fat readings as
an illustration, the formula would give the following
results:

32.5-4=8.12

1.2X4.2—=5.04

8.12+5.04-++.14==13.30% S.N. F.

A DAIRY LABORATORY GUIDE 31

The following example will illustrate how a
knowledge of the per cent of S. N. F. of a sample
of milk is utilized in figuring adulteration per cents:

Before adulteration a sample of milk had 4.2 per
cent of fat and 9.0 per cent of S.N. F. After adul-
teration the sample contained 3.1 per cent fat and
7.5 per cent of S. N. F. The following questions
can be answered from calculations with the above
data:

1. What per cent of water was added to the
milk?

2. At what rate per cent was the water added?

3. What per cent of the fat was adulterated
by skimming?

4. What per cent of the fat was adulterated
by watering?

(1) Since there were 9 parts of S. N. F. before
adulteration and 7.5 parts of S. N. F. after adultera-
tion, 1.5 must have been removed by adulteration.

9—7.5=1.5
1.5+9-=16.66% of S. N. F. removed by adding
the water.

Since 16.66 per cent of S. N. F. was removed,
water is the only thing that could have taken its
place; therefore 16.66 per cent of water was added
to the milk.

(2) For every 7.5 parts of S. N. F. in the milk
1.5 parts were removed, or in other words water
was added at the rate of 1.5 parts of water to every
7.5 0f S.N. F.

The rate per cent at which water was added
would be 1.5+7.5=20%.

Before adulteration the sample had 4.2 parts fat
and after adulteration 3.1 parts fat, 1.1 parts of fat
were removed, which equals 26.19 per cent.

I.1-+4.2==26.19%.

32 A DAIRY LABORATORY GUIDE

When milk is watered all of the solids are re-
duced in the same proportion. It has been found that
16.66 per cent of the S. N. F. was removed by water-
ing; therefore, according to the above rule 16.66 per
cent of the fat must have been removed by water-
ing. But 26.19 per cent of the fat was removed;
therefore the difference between 26.19 per cent and
16.66 per cent will show what is removed by skim-
ming; 26.19—16.66=9.53% removed by skimming.

A DAIRY LABORATORY GUIDE 33

EXERCISE V

BABCOCK TEST AND QUEVENNE
LACTOMETER

1. Test in duplicate by the Babcock method a
sample of whole milk as follows:

(a) Use ordinary amount of acid.
(b) One-half usual amount of acid.

(c) Fill the bottle up to the base of the
neck with acid.

(d) Use the regular amount of acid, but
warm the acid and milk before mix-
ing until they feel warm to the hand.
Add the acid slowly to the sample.
Observe and record all results care-
fully.

Test for fat a sample of butter. Why is it ad-
visable to add the acid slowly in (d) ques-
tion 1?

2. (a) Take a Quevenne lactometer reading of a
sample of whole milk and skimmed
miilk, making corrections for tempera-
ture.

Explain fully the effect of temperature on

the lactometer readings.

(b) Starting with the first reading in 2 (a),
what would have been the reading if
the temperature had been 54° F., 62°
F., 73° F., 81° F.?

3. Add one-half an acid measure of water to the

skimmed milk sample and take the Quevenne

34 A DAIRY LABORATORY GUIDE

reading. Note any change in the lactometer
reading, and explain the reasons for this
change.

4. Take the Quevenne reading of a sample of
skimmed milk.

Compute what the reading would be if the tem-
perature were four degrees higher. Verify
your results by warming the sample and tak-
ing the reading. Be sure to mix the sample
thoroughly after warming it. Have the tem-
perature of the milk low enough so that rais-
ing the temperature four degrees will not
bring the sample above 70° F. Why should
not the temperature be above 70° F.?

What is the chief advantage of the Quevenne
lactometer over other kinds?

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35

36 A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE 37

EXPLANATION. BOARD OF HEALTH
LACTOMETER

The Board of Health lactometer (commonly called
B. of H. lactometer) is an instrument giving ar-
bitrary readings and it must be changed to equiv-
alent Quevenne readings in order to obtain the
specific gravity. It is of the same general shape
as the Quevenne, except that the thermometer
scale is usually on the opposite side of the stem
from the lactometer scale. The instrument is
graduated from o to 120, and one degree Board of
Health equals .29 of one degree Quevenne. In
order, therefore, to change from Board of
Health to Quevenne, the Board of Health
reading is multiplied by .29. Vice versa to
change from Quevenne to Board of Health reading,
the Quevenne reading is divided by .29. Like the
Quevenne, the Board of Health lactometer is gradu-
ated to be read at a temperature of 60° F., and if
the temperature is above or below the standard,
the correction factor is .3 of one lactometer degree
for every degree that the sample is above or below
the standard. The following example will illustrate
how correction is made: B. of H. reading 110.5 at
65° F., what would be the reading at 60° F.? The
sample must be cooled down 5 degrees; therefore,
we would add 1.5 (5X.3) to the reading (110.5),
making a corrected reading of 112.0. One of the
chief advantages of the B. of H. lactometer is that
a small adulteration of the milk will make a notice-
able change in the lactometer reading. This is be-
cause the instrument has so large a scale. Also,
when milk is watered, the number of. lactometer
degrees recorded below 100 indicates roughly the
per cent of adulteration.

38 A DAIRY LABORATORY GUIDE

EXPLANATION. USE OF HAND MACHINE
IN BABCOCK TEST

It is a popular notion that milk cannot be tested
accurately in a hand machine. This is a mistaken
idea, as a hand machine should do as good work as
any other machine. One of the chief reasons for
inaccuracy in using a hand machine is the inatten-
tion paid to the temperature. It is necessary to
have the proper degree of heat in order to perform
properly the Babcock test. To provide the proper
temperature the hand machine should be filled with
hot water up to the bottle cups if the room is at all
cold. The small two-bottle and four-bottle hand
testers have no frame, and so the bottle cups are
made large in order that they may be filled with
hot water if necessary. While it is not absolutely
necessary to use hot water at all times, its use is
always advisable. By its use the danger of test-
ing milk at too cold a temperature is largely done
away with. The operator should be careful to keep
the machine to its proper speed during the entire
run.

A DAIRY LABORATORY GUIDE 39

EXERCISE VI

BABCOCK TEST AND B. OF H.
LACTOMETER

1. Take the B. of H. lactometer reading of a
sample of whole milk. Remove the lactometer,
measure out two bottles for the Babcock test and
allow the milk to stand in your lactometer cylinder
while you do No. 2. Then draw off from the top
of the sample all the cream the pipette will hold.
Then add to the sample 17.6 cc. of water. Again
take a lactometer reading and make a Babcock test
and figure out the per cent of fat removed by skim-
ming and the per cent of fat removed by watering.
After drawing off cream and adding water be sure
to mix the sample thoroughly. Upon what rule
does your ability to do the above computation de-
pend? Better results will be obtained if the milk is
warmed to about 85° F. and allowed to stand as
long as possible. In removing the cream keep the
point of the pipette as near as possible to the sur-
face of the liquid.

2. Test in the steam machine whole milk, skim-
med milk and butter. Run the skimmed milk ten
minutes, two minutes and one minute. Use acid
one-quarter inch above the mark. Retest the whole
milk in the hand machine and compare the results
with those obtained in the steam machine.

3. (a) Take the B. of H. lactometer reading
of a sample of skimmed milk. See how much water
it will take to lower the lactometer reading one
degree. Great care must be taken to mix the water
with the milk as the former is poured in. This is

40 A DAIRY LABORATORY GUIDE

best done by pouring the milk from one vessel to
another.

(b) See if one-half gram of salt will bring the
reading back to where it was originally.

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42

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STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE 43
EXPLANATION. ACIDITY OF MILK

The acidity of milk is of two kinds—apparent
and real acidity. The apparent acidity is due to
the acid reaction of the acid phosphates and casein.
The real acidity is due to the presence of lactic
acid (C3HgO3), which is produced by the action of
bacteria upon the sugar of the milk. The follow-
ing reaction is supposed to be the one which takes
place:

Cy2H22011;+H2,O=4C3HgO3

The apparent acidity, according to Van Slyke,
does not go above .08 per cent to .1 per cent, and is
of minor importance so far as dairy work is con-
cerned. In determining the acidity of milk it is as-
sumed that all of the acidity is due to the presence
of lactic acid.

The real acidity will ordinarily go as high as 1
per cent, and in some cases higher. Usually, how-
ever, when from .8 per cent to I per cent acidity
is reached the lactic acid organisms will cease
working. If a part of the acid is neutralized the
organisms will again commence the production of
acid.

Lactic acid is important in the manufacture of
dairy products. For example, butter is churned
from cream which is soured or “ ripened” by lactic
acid. The presence and amount of lactic acid is
very important all through the process of cheese
making. In many cases the nature of the product
depends on the amount of acid present during the
successive steps of manufacture.

For these reasons it is necessary to have some
means of finding the amount of acid in the milk.
The process by which this is done is called titration,

44 A DAIRY LABORATORY GUIDE

It is a principle of chemistry that an alkali will
neutralize an acid. In order, therefore, to find the
acid in the milk we take a known quantity of the
milk and measure into it an alkali whose strength
we know. The instrument used to measure the
amount of alkali used is called a burette, and the unit
of measure is the cubic centimeter. It is commonly
graduated as fine as tenths of a cubic cen-
timeter. One can tell when all of the acid is neu-
tralized by means of an indicator. The indicator
used most in dairy work is phenolphthalein, which is
colorless in acid and pink in alkali. If two or three
drops of the indicator are put in milk the color will
not change, because the milk is acid in reaction.
The instant that just enough alkali is added to the
milk to neutralize all of the acid the solution will
turn pink.

It is a chemical fact that equal volumes of acids
and alkalies of the same strength will exactly neu-
tralize one another. In 1 cc. of a normal solution
of lactic acid there are .og grams of lactic acid.
According to the above rule I cc. of any normal
alkali solution would just neutralize .o9 grams of
lactic acid.

In actual practice a solution weaker than a normal
solution is usually employed, because a normal solu-
tion is so strong that any small variation in the
amount used makes a big variation in results. A
common solution used is 1/10 normal (expressed
n/1o). One ce. of an n/1o alkali solution would
neutralize .oo9 grams of lactic acid. An example
will illustrate how the per cent of acid in milk is
calculated. Suppose it took 6 cc. of n/io alkali
solution to neutralize the acid in 20 grams of milk.
What is the percent ofacid? Onecc.ofn/to alkali
will neutralize cog grams of lactic acid. Six ce. will

A DAIRY LABORATORY GUIDE 45

neutralize 6X.009==.054 grams of acid. .054-+-20=
.0027. .0027X 100==.27% acid in the milk. Formu-
lated, the above example is expressed as follows:

:009x6 —
a X 100.27 %

If the milk for the acid test is measured in cubic
centimeters it should be reduced to grams by mul-
tiplying by the specific gravity of milk. The acid
is obtained in terms of grams and we cannot divide
grams by cc. and obtain per cent.

Professor Farrington has devised some alkali
tablets, each one of which will neutralize .03492
grams of lactic acid. These tablets are dissolved
in water and an alkali solution made. The strength
of the solution per cc. will vary according to the
number of tablets used and the number of cc. of
water in which they are dissolved. The indicator
is added to the tablets when they are manufactured.
Consequently, when using an alkali tablet solution
no phenolphtholein is needed. A concrete example
will show how these tablets are used.

Suppose that it required 15 cc. of an alkali tablet
solution to neutralize the acid in 20 grams of milk.
The tablet solution was made by dissolving five
tablets in 100 cc. of water. What is the per cent
of acid in the milk?

.03492—grams of lactic acid one tablet will neu-
tralize. .034925=.1746 grams of lactic acid five
tablets will neutralize. Since the five tablets are
dissolved in 100 cc. of water .1746 is the amount of
lactic acid too cc. of the solution will neutralize.
Then .1746+100==.001746, the strength of 1 cc. of
the solution; in other words, the number of grams
of lactic acid 1 cc. of the solution will neutralize.

.001746X 15==.026190
.026190-+20==.001 3095 X 100=.1 3095 %

46 A DAIRY LABORATORY GUIDE

If five of the alkali tablets are dissolved in 97 cc.
of water each cubic centimeter of the solution will
neutralize .o1 per cent of acid when 18 grams of
milk are used. This solution is often used by
creamerymen, as the per cent of acid may then be
read directly from the burette. Many devices for
testing the acidity of milk are on the market, all
tending to do away with computation and giving
the percentage of acid directly. One of these is
Publow’s acidimeter. In this apparatus an n/Io
alkali solution is used and 9 grams of milk are
tested. Each cc. on the burette equals .1 per cent
of acid and each 1/10 of a cc. equals .ot per cent
acid. In testing for acid one should always try
and obtain the same degree of color each time.
This color should be permanent for at least one
minute. Great care should be taken not to run in
an excess of alkali. It will be much easier to detect
the color change if some water is added to the

sample after it is measured out before the alkali
is added.

‘

A DAIRY LABORATORY GUIDE 47

EXERCISE VII

BABCOCK TEST AND ACID TEST

(a) Test by the Babcock method, butter, cream
and whole milk. Compute the weight of
the fat column in the cream test.

(b) Retest the whole milk, putting 9 grams in
one bottle and 5 grams in the other. Re-
duce each reading to a basis of 18 grams.

(a) Test the skimmed milk for per cent of
acid, using n/io alkali solution, and
using 18 grams of milk.

(b) Retest the skimmed milk, using 25 cc. of
milk and compare with first test.

(c) Measure out 18 grams of skimmed milk and
add to this 17.6 cc. of water. Test for
acid and compare with the first test.

(d) Measure out 20 cc. of skimmed milk from
same sample as used in above experi-
ments and add to it 3 cc. of buttermilk
or starter and test for acid. What is
the object of using different amounts in
(a) and (b)? What is the object of
adding water to (c)?

Take the B. of H. lactometer reading of the
whole milk and compute per cent of T. S. and
S. N. F.

Take a lactometer reading of skimmed milk.
Cool the milk as low as possible and compute
what the reading would be at this tempera-
ture. Then compare your computation with
the actual reading.

48 A DAIRY LABORATORY GUIDE

Perform the same experiment, heating the milk
to 95° F. The object of this experiment is
to show the incorrectness of a correction
factor when used at a temperature of more
than 10° F., either above or below 60° F.

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50

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STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE 51

EXPLANATION. EFFECT OF SPEED OF
MACHINE ON BABCOCK TEST

The following exercise illustrates the influence of
the speed of the machine on the amount of fat
brought to the surface. The speed of the machine
is important, because the greater the speed the more
force exerted. One should always run a Babcock
tester up to the speed indicated in the directions for
running the machine. Sometimes one will make as
good a test when running a machine slow as when
running faster. This, however, is not always the
case, and in operating the tester one must be sure
that the machine is run fast enough to bring all of
the fat into the neck of the bottle.

52 A DAIRY LABORATORY GUIDE

EXERCISE VIII
BABCOCK TEST AND LACTOMETER

1. (a) Test by the Babcock method a sample of
whole milk, skimmed milk and butter.

(b) Retest the butter in the hand machine.

(c) Retest the whole milk in the steam ma-
chine, but do not let the speed of the
machine exceed 250 revolutions per
minute.

In performing the above experiment it is
best to experiment with the machine
before putting in your samples. Other-
wise, you will be liable to run the ma-
chine too fast.

2. (a) Take a lactometer reading of the whole
milk and figure out the S. N. F. and
eS

(b) Take a lactometer reading of the skimmed
milk and figure out the S. N. F. and T.S.

3. (a) Test the skimmed milk for acid with n/to
alkali solution and the alkali tablet solu-
tion. The alkali tablet solution was
made by dissolving eight tablets in 95 cc.
of water.

(b) Test for acid 18 grams of tap water. Add
to 18 grams of tap water 3 cc. of starter
or buttermilk, again test for acid. Use
n/1o alkali solution.

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53

54

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STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE 5

tat

EXERCISE IX

BABCOCK TEST. LACTOMETER READING
AND ACID TEST

1. Make a Babcock test of cheese, whole milk and
skimmed milk. Add acid to the skimmed
milk about one-quarter of an inch above the
usual mark, and run ten minutes, two min-
utes and one minute.

Run the whole milk the usual time at the usual
speed. Be sure to cut the cheese fine before
putting into the test bottle.

2. (a) Retest the whole milk, running the machine
one minute, one minute, one minute. Do
you get any different results either in the
amount or the appearance of fat? If so,
give the reasons.

(b) Retest the whole milk, running the machine
fifteen minutes, five minutes and three
minutes. Do you get any more fat than
when the machine is run the usual length
of time?

Oil the machine well before each run.

3. Take the B. of H. lactometer reading of
skimmed milk and whole milk. Make correc-
tions for temperature and figure out the
S.N.F. and T. S. For whole milk use three
formule.

4. Test the whole milk for acid, using 18 grams.
Use both n/to and alkali tablet solution.
Test the skimmed milk for acid, with the n/1o
solution. Use only § cc. of the milk, so that
one result will be a check on the other.

56

A DAIRY LABORATORY GUIDE

Again test the skimmed milk, using a 50-cc.
sample. Do this twice. See if you get the
more uniform results with the large sample.

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57

58

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STUDENT’S NOTES AND REPORT

to

A DAIRY LABORATORY GUIDE 59

EXERCISE X
BABCOCK TEST AND ACID TEST

Make up an alkali tablet solution as directed.
Shake frequently, and set aside for use later
in the exercise.

(a) Test by the Babcock method a sample of

whole milk and a sample of butter.

(b) Place a piece of butter in your acid measure
and allow it to stand in a cup of hot
water for about fifteen minutes. Then
with a pipette draw the fat from the sur-
face of the liquid, and test by the Bab-
cock method. What conclusions do you
draw from this experiment?

Test for acid a sample of starter, using the
alkali tablet solution furnished and n/1o
alkali solution.

Pour back and forth from one vessel to another
about 100 cc. of skimmed milk. Do this for
about three minutes. Test 25 cc. of it for
acid, using the alkali tablet solution which
you made up at the beginning of the exer-
cise. Then boil about 35 cc. of the milk for
about one minute; cool; keep covered while
cooling, and retest 25 cc. for acid. Compare
with first test and see if you get lower
results.

Explain fully why lower results may be ex-
pected with boiled milk.

The alkali tablet solution was made by dissolv-
ing 10 alkali tablets in 115 cc. of water.

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STUDENT’S NOTES AND REPORT

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61

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EXPLANATION OF EXERCISE X

In testing butter by the Babcock method, the
practice is sometimes followed of melting the
butter and then putting it into the test bottle
by means of the pipette. It is possible to do
this sometimes and get accurate results, but
the tendency for fat and water to separate
makes it difficult to get accurate tests.

Divisionbof experiment 2 illustrates how readily
the fat and water separate. In drawing off
the fat for this experiment, keep the point of
the pipette at the surface of the fat.

Carbon dioxide acts toward an alkali like an
acid. We are told that some of the acidity
of the milk is due to the presence of COs.
In experiment 4, pouring the milk back and
forth from one vessel to another tends to mix
the COs of the air with the milk. Heat will
expel the COg, and so after boiling the milk
the acid test would be lower than it would
be before boiling. This experiment also
shows that milk will take up gases.

A DAIRY LABORATORY GUIDE 63

EXERCISE XI

BABCOCK TEST AND BUTTER MOISTURE
TEST

1. Test a sample of cheese, whole milk and
skimmed milk for butter fat. In testing the
skimmed milk, run extra time and use extra
acid as previously directed.

2. Test cheese for acid, using n/1o alkali solu-
tion. In order to test cheese for acid, weigh
out 3 grams. Place in a white cup and add
17.6 cc. of warm water. Then with a stirring
rod gririd the cheese up as fine as possible.
This will take at least five minutes. Then
test the solution as usual, and calculate the
per cent of acid.

3. Test a sample of butter for moisture by the
C. U. method.

Note.—To what is the high acid content of
cheese due?

64 A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

65

66 A DAIRY LABORATORY GUIDE

EXERCISE XII

BABCOCK TEST, LACTOMETER AND ACID
TEST

1. Test by the Babcock method a sample of whole
milk, cottage cheese and buttermilk. Fill
your lightning top sample jar about one-third
full of whole milk, add a preservative tablet
and shake at intervals until tablet is dis-
solved. Set the sample away in your desk
and test at the next exercise.

Use 9 grams of cottage cheese, and add 9 grams
of water. Test in whole milk bottle. Shake
well after adding acid.

2. To about 54 grams of skimmed milk add 2 cc.
of light machine oil, shake thoroughly and
test in duplicate by the Babcock method.
Compare the appearance of the fat column
with that obtained with ordinary butter.

3. Test with the alkali tablet solution the acid in
the whole milk and buttermilk.

4. Take a lactometer reading of the whole milk.
Add some water (about 25 cc.) to the
sample. Again take a lactometer reading
and make a Babcock test. Figure out T.S.
and S. N. F. and the per cent of the water
added.

A DAIRY LABORATORY GUIDE 67

STUDENT’S NOTES AND REPORT

68

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

A. DAIRY LABORATORY GUIDE 69

EXPLANATION. COMMERCIAL RENNET
AND ITS USE

Commercial rennet is a liquid prepared by soak-
ing in brine the fourth stomach of the calf. It has
under certain conditions the power of precipitating
the casein from milk. It is so desirable for this
purpose that rennet is used almost exclusively in
the manufacture of cheese. One peculiar character-
istic of rennet is the fact that it is not destroyed
by its use in precipitating casein. If it could be
extracted the same rennet could be used over and
over again for precipitating the casein in different
lots of milk.

Temperature has a decided effect upon the action
of rennet. The colder milk is, the less rapid the
rennet action. This is very noticeable at tempera-
tures below 80° F. The rennet acts most rapidly
at temperatures from 100° F. to 120° F. At 130°
F, the action of the rennet is less active and its
action is entirely destroyed somewhere between
140° F, and 150° F. The high temperature destroys
the rennin, which is the active principle of the
rennet. The action of rennet increases as the acid
in the milk increases. The action of rennet seems
to depend to a great degree upon the solubility of
the lime salts of the milk. If an insoluble lime
salt is added to the milk, the action of the rennet
is retarded, and if a soluble lime salt is added to
milk the action of rennet is hastened. If milk is
heated to a high temperature the lime salts are
supposed to be rendered insoluble and the rennet
has no effect on the casein. Freezing does not seem
to injure rennet. When it is again melted and
given the proper temperature it will act as though
it had never been frozen.

7O

A DAIRY LABORATORY GUIDE

EXERCISE XIII

BABCOCK TEST, MICROSCOPIC APPEAR-

ANCE OF MILK, USE OF RENNET

Test the composite sample preserved at the last
exercise.

Examine under the high-power microscope
cream, whole milk and skimmed milk. Make
a drawing of each field. Describe fully the
difference in the appearance of the fat
globules in each of the three fields.

Heat 18 grams of skimmed milk to about 100°
F. and add four drops of rennet; shake thor-
oughly and let stand. Note the length of
time it takes the milk to curdle.

To one-half a teacup of water add six drops of
sulphuric acid. Add three drops of this solu-
tion to 18 grams of milk. Heat to about
too” F, and add four drops of rennet and
note the time it takes for milk to coagulate.
Compare length of time with that required
in No. 3.

To about 20 grams of skimmed milk add six
drops of sulphuric acid and shake thoroughly.
Note time it takes the milk to coagulate and
compare the coagulum with that obtained
when rennet is used.

Measure out two 25 cc. samples of skimmed
milk. Warm to 80° F. To one sample add
five drops of rennet; to the other add five
drops of sulphuric acid. Note and compare
the length of time it takes each to coagulate.

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

71

72

A DAIRY. LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

=

2

A DAIRY LABORATORY GUIDE 73

EXERCISE XIV
BABCOCK TEST AND USE OF RENNET

Test by the Babcock method a sample of butter-
milk and a sample of skimmed milk cheese
and whole milk cheese. Compare the results
of the cheese tests.

Boil a sample of milk for about two minutes and
then cool. Add some rennet and see if the
milk will coagulate.

Boil 25 cc. of milk for about two minutes and
then cool. Add one-half cc. of sulphuric acid
and see if the milk will coagulate.

Add to 25 cc. of milk six drops of rennet. Have
the temperature of the milk at 100° F. Note
the time it takes the milk to coagulate. Test
25 cc. of the same lot of milk for acid. Com-
pute the amount of n/1o alkali necessary to
neutralize the acid in 50 grams of the milk.
Divide the milk into two portions of 25 cc.
each and bring the temperature of each to
100° F. and add to each six drops of rennet.
Note the time it takes the samples to co-
agulate. Compare with the length of time
required to coagulate the milk before the
alkali was added.

74

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

76

i.

22

A DAIRY LABORATORY GUIDE

EXERCISE XV

BABCOCK TEST AND LACTOMETER

READING

Take a lactometer reading and make a Babcock

test of a sample of whole milk. Compute the
T. S. and the S. N. F. Allow the sample to
stand in the lactometer cylinder while you
do No. 2. Then remove all of the cream pos-
sible and add 25 cc. of water. Again make
a Babcock test. and take a lactometer read-
ing. Compute the per cent of water added,
the rate per cent at which water was added,
the per cent of fat removed by skimming.
the per cent of fat removed by watering and
the rate per cent at which the fat was re-
moved.

Test in the steam machine a sample of whole

milk, and a sample of butter. Retest a
sample from the same lot of milk in
the hand machine and fill the machine
with water at 60° F. Note the result
of the low temperature upon the fat column.
Run the same bottles which were tested in
the hand machine in the steam machine for
a period of three minutes and then read the
fat column. Note if there is any increase
in the fat column.

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

77

78 A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE 79

EXERCISE XVI

USE OF RENNET. PRECIPITATION OF
ALBUMEN

1. Take 18 grams of milk in a white cup and cool to
so° F. Add four drops of rennet and note
time it takes the milk to coagulate. Com-
pare this with the same amount of milk
warmed to 85° F., to which four drops of
rennet have been added.

2. Boil some whey and note the albumen which is
thrown down in a white flocculent pre-
cipitate. Fill your lightning top sample jar
about one-half full of skimmed milk at about
too” F. Add 1 cc. of rennet. Set aside to
coagulate. Then strain off the whey and
precipitate the albumen in the whey by boil-
ing.

In both cases the boiling should be done in a
test tube. It may at first be difficult to see
albumen, as it is in very fine particles. The
albumen may be distinguished more readily
by holding the test tube between the eye and
the window.

Turn in desk, key and locker. See that all glass-
ware is clean before turning in the desk.

80

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

A DAIRY LABORATORY GUIDE

STUDENT’S NOTES AND REPORT

81

INDEX

F PAGE
Acid:
TACHC: acta Saatieteet cases SRA ae 43
IMECASUIEE: “acs seussecedtungeserararediepnraceneinectienmeave dara cuangeeleseoie’ 5
In Milk .......... rita bene anetiadybad ena OURS a eo uaesTe 43
SUDMUPICS sieceneedas meu aeetodls cra equ hme tain seanaaase 5
Acidity :
Apoarentiand: teallec c.aadsediwvesinerwiu sake seein aes 43
As: effected iby GOn. + evccavsacie ved paeewass aaneeaNese 62
Alkali. Tablet. Solution..........c8c¢sss0s.aaeesvd sannaces 45
BabeGck: TROS€ «a csidscscsasaneytitneucas (ol eracddvayeabarsivaua toscana vecdiigsst Rane 5
Boiled! Milks Lest inacc.qsisvculncnerdsaaadans wmacwa petiadenetas 18
BRUT O EEE: bode desi fever scape riven eacatses eke aed wanna edna etal 44
Butter: Hat! 4. csncanasasguansaiscramune samara nares 2
Melting: point: cacsansssosayesassies ceeded Pe commer 3
Moisture it)... 00 sicese severe yeeeeeods HNN aes May 19
Preparation, for’ fat. test... .......neveweoessoresessee sce 19
Preparation for moisture test............. 0.0 e cece eae 23
(CAS GLY fers craonhasapcacnuen me ndaalarnaen ena ns ao ne uote een eae 3
Amount ineomille scccasiccesacreacc ieee sec tn da ac eadanaearccaateuirn 3
Gharacteristtes: Of seus adie vein caecaay be leeelenieas wee 3
Commercial: wses; (Of scx ewraatarnsimsiaclanmilonalnciumenssaacics 3
Collodial; state’ <:-4cnecxa cn iak vaulnamws entire navasine 3
Cornell Moisture Test............. cece ceeee ce eeee reece 23
Cream ..........- iiss dv Bus flcay aud coats uot dross sb Sade dvevenzyeasatuscacditavoea 7
Viscosity of ..... pari ia toate eGr non els eaanen tyres 7
Weighing for’ testing sss s:s-cccsciesaccteisiaie ioe tie-alereerare) suave slave 7
Fat) 2ccsnk sinnaans seine se peawulnGne Leathe ieee sxeer 1
Composition Of scaciscorcwwesasersode meee swarmannanas 3
Formaldehyde: Test ou... cccn004 cceaaaeinmeaniasnense 18
Gala Chase: wiaolayessdecpnantesieroavtesiaee sraae ca eauond nialemeha. arena PUR 18
Tin iCAbOR jeteccuicscovanseing wig chis etek dabace ination sana ape tenatcoabaea-asarineld dow dotecs 44
Lactometen iccecdwstehntheoceu caaiee de eG atg emu saa eiiets”s 27
Board Of Heéalthiec+s.ccecave causes enagawe re eaeees ae 37
QUEVENNE canccicicoesdecarsesaneseasssseeoensse wines 27
WISE: Gt: jacks wpevace! ote edvenese witreacd du slat shiesuas hes tu oehedd aedehusneontane ates 29
Machines: sixcwsurasaceiad saci oannw andieandnetenhs San means 6
Phan etaccbece nctscrccpesacc tetas srapetlatonelel d qrvlinitie sens eauonetaceverncaigrenciiuisinians 38
Effect of speed ‘On teStissicnkcesca ae necten eneenneeeweie 51
Melting Point of Butter Fat............. eee eee cece 3

84 DAIRY LABORATORY GUIDE

IMIG: arerces sci ciataemeinta's ote eae ne omeeintie es sp oeeee nee
Adultération: . specowinse ss o2444 4 anseuangian se reseeeeee
Albumen, 1, ssccssenscceesssae% eens a dane eens ae
ASH AM, 564 ccAaetiese Rae y tees 824 wee ERRRM Dobe es aaa TSS
Composition Of v.26 ek oi ee Ga eencsithaae eens eae aT
GAS eli bin 5 Seay acaencigaidisacee tutes SOM Red eer inewsuedenneehe eRe 2G
UREN esas. apis rrehoucusteanne haa ae een aieei dein aih Bate sed

WrateP ities. onmavinaiese cores ws sia a aend deipeibee eae Wiel ow lciela ts
Phenolphthaletn: « scugnisengiesaecwg maseameuawrs oboe eee
Pipettes. ssisg vaasiienwns java adseabaneteaa’dseaa vas oo
Reading; Bat Column. sada veces dss oad deatreesaw seen s e445
Rennets « svsssaaenemensawy oy2eh4a £4 va taneake seas ee

Specific: Gravity acecieeacee en oes nes oe OAIGIAE yee NSKRRA
MIN seas ae eiiabeavoe wes oes cae aly akiae bees wed eek ona ae

Sktinnle d Milk a aysinessusseiiee Soe ecasd gv eee wiiegesvvaveerake date once

WEY ou iore as hennredanclans Seated 4 acthwerouineunhs eas peda Deca

Whole: Mille wcaccnndamsua ate ose Gun sieduamape caine ee 26 seed
Temperature :

Effect on lactometer reading......... 0.0... .ccceeeeeee

Effect on fat column........... 00. c ccc c eee eencceucuas

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