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PASTEURIZATION OF MILK

FROM THE PRACTICAL VIEWPOINT

A HANDBOOK RELATING TO THE INSTAL-
LATION, OPERATION AND CONTROL OF
PASTEURIZING PLANTS. USEFUL TO

MILK DEALERS, STUDENTS IN DAIRY
SCHOOLS, PUBLIC OFFICIALS HAV~
ING CONTROL OF MILK HAND-
LING, AND OF INTEREST TO
THE GENERAL PUBLIC

BY
CHAS. H. KILBOURNE

LATE CHIEF OF THE DIVISION OF PASTEURIZING PLANTS
NEW YORK CITY DEPARTMENT OF HEALTH

NEW YORK
JOHN WILEY & SONS, Inc.
LONDON: CHAPMAN & HALL, LIMITED
1916

SF259
(KG

Copyright, 1916
By CuHas. H. KitBouRNE

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INTRODUCTION

In presenting this book on the pasteurization
of milk, the author has endeavored to so handle
the subject that the milk dealers, the students in
dairy schools, and health department officials who
are charged with the supervision and control of
the milk sold in their communities, will find in the
book practical assistance in their work. Except
for the excellent bulletins issued by the United
States Government, there are few books which deal
with the practical aspects of milk pasteurization,
and the author felt that a real need existed for
such a work.

It is possible that his long association with the
milk work, as it has been carried on by the New

York City Department of Health, has somewhat

colored his views with official conservatism. He

has tried, however, to be fair and impartial, and to
look at matters from the dealers’ point of view.
He has presented freely practical lessons which

ill

INTRODUCTION

he has learned during a somewhat wide experience
in investigating pasteurizing plants.

If any dealers with questionable motives look in
this book for practical suggestions by which they
may be able to save milk and cream which is going
bad, or if they wish to learn how departmental
regulations can be evaded, they will be ‘disap-
pointed.

It is hoped, however, that dealers who honestly
desire to handle milk so that it will be safe and
salable will find assistance in this book.

The author wishes to acknowledge the assistance
and good advice which he has received from Dr.
Wm. H. Park, Dr. Chas. F. Boldune, Ole Salthe
and James E. Thomson, and from Inspectors
Ryan, Lee and others in the New York City De-
partment of Health. Also he wishes to thank the
various manufacturers of dairy machinery for in-

formation given and illustrations supplied.

C. Eck

New York, September 1, 1916.

IV

The Pasteurization of Milk from the
Practical Viewpoint

CHAPTER I

PASTEURIZATION IN GENERAL

The guarding of food supplies in large towns
and cities is one of the most important functions of
government activity. This activity, like all forms
of organized effort, has been a gradual develop-
ment. In the most primitive communities, individ-
uals naturally felt a certain care over the food
which they ate. This interest was instinctive and
fundamental, since each individual was conscious
that some foods were dangerous. He therefore
obeyed the law of self-preservation when he se-
lected his food.

As the homes of individuals became more con-
gested on account of the increase in population,
it grew to be increasingly difficult for the indi-
vidual to select the food which he ate. He there-
fore came to depend more and more upon the
judgment of other people who had either used
similar food before or else knew how it was pro-

1

THE PASTEURIZATION OF MILK

duced. The substitution of the judgment of oth-
ers for his own personal inspection of food nat-
urally developed into a certain sort of communal
or public control of foods. As communities be-
came more and more congested, it became neces-
sary to centralize the control of foods under some
definite organization. This centralized control,
which was usually at first vested in some private
organization, was later taken over by the govern-
ment which obtained in the town or city. Thus we
have the Boards of Food Control, which are now
usually centered in the Health Departments.

As the inter-dependence of the various towns and
cities. became more fully recognized, it became evi-
dent that not only the cities but the states should
on broad lines, regulate the production and sale of
foods. This state regulation of foods has been cen-
tered partially in State Health Departments, partly
in the Agricultural Departments and sometimes in
special departments whose duties have been to
control the foods sold in the state. These state
departments are becoming increasingly efficient as
the good work which they do is becoming more and
more recognized.

Since the means of communication and transpor-

2

FROM THE PRACTICAL VIEWPOINT

tation are becoming more rapid, the effect is that
the world is becoming smaller, and so the consump-
tion of foods is not confined to the states where it
is produced. The increasing use of cold storage
facilities for preserving foods also adds to the wide
area from which cities and towns can obtain the
foods which are there consumed. It, therefore,
becomes evident that state regulation is too narrow.
In order to properly protect the citizens, therefore,
the general government has taken up, to a large
extent, the control of foods which enter into inter-
state commerce, and government standards are
adopted.

Among the articles of food which have perhaps
received the largest share of attention we find milk.
This attention has been deserved on account of the
almost universal use of milk, and also on account
of the fact that it becomes easily infected with
dangerous bacteria, and having become infected it
is itself an ideally good medium for their growth.
The milk thus becomes so changed or decomposed
that it is frequently unsafe for food. The oppor-
tunities for infection are many, on account of the
many persons through whose hands it passes be-
fore it reaches the city consumer, and where it is

3

THE PASTEURIZATION OF MILK

perhaps fed to the children who depend upon milk
for their life. At any point along the line of
travel from the cow to the consumer it may be-
come dangerously infected. If the cows from
which it is drawn are not healthy, the milk may
start on its journey in an unsafe condition. Even
if it is perfectly wholesome when drawn from the
cows, it may at any point along its line of travel
become changed from its natural state.

Disease-producing bacteria or other less harm-
ful germs may enter the milk from stable dust or
from the manure and urine which drops from the
cow herself. The milk bottles and cans may have
been carelessly washed or the water with which
the washing is done may be from contaminated
sources. Diseased, or unclean persons may be em-
ployed in milking the cows, or in handling the
milk after it is drawn. Cans or bottles in which
the milk is placed may have been returned from
the consumer in filthy condition and have been
again used for containing fresh milk before being
thoroughly washed and sterilized. Contagious dis-
ease may have been in the homes from which they
are returned. 3

Much of the milk in large cities is handled at

4

FROM THE PRACTICAL VIEWPOINT

creameries or shipping stations which are located
in the country and from which the milk is shipped
to the cities. Thus, there is an added opportu-
nity for milk infection on account of the insani-
tary buildings or from coming in contact with
dust-laden air or diseased employees. Once hav-
ing gained access to the milk the growth and mul-
tiplication of the germs is aided by the powerful
agencies of age and heat. If germs which pro-
duce disease get into the milk the danger that epi-
demics of disease will occur is a serious one. Each
point in the handling of milk is therefore an im-
portant point, for the chain of milk safety is only
as strong as its weakest link.

Aside from the danger of bacterial contamina-
tion there is of course the possibility of actual
adulteration being practised within the legal defini-
tion of that term. Foreign substances may be
added, such as water, coloring matter, preserva-
tives, etc., or the cream may be removed. Such
adulteration may be accidental or it may be de-
liberately practised, with “malice aforethought,”
with intent to deceive and defraud the final con-
sumer, for the purpose of increasing the profits.
On account of the sharp competition which ex-

5

THE PASTEURIZATION OF MILK

ists in modern trade, some dealers consider that
they are justified in doing some things which are
objected to by public boards of control. Some-
times milkmen will endeavor to save a perishable
product by the use of preservatives. This form of
adulteration, however, is at present very little
practised.

The importance which attaches to the public or
communal control of milk is not the only force
which is lifting to a higher level the character of
the milk sold to the public. Milk dealers them-
selves are realizing more and more that modern
conditions are such that only the best and the
most efficiently produced and handled product can
remain in the market. They are therefore be-
coming more and more active in establishing
means for effectively controlling their own sup-
plies. The methods employed are various. Asso-
ciations of men have been formed, the object of
which is to secure mutually useful advice and to
give each other the benefits of individual expe-
riences.

The larger dealers establish within their own
organizations an efficient inspection service and
seek by means of laboratory tests and research

6

FROM THE PRACTICAL VIEWPOINT

work to study their problems and so seeure the
best milk possible at the least expense, and with
the least amount of waste. Thus the governmen-
tal forces and the dealers themselves both work
toward the goal of a better milk supply.

The great importance of the problems which
affect the securing of a safe milk supply has led
to the publication of many books, in which the va-
rious phases of the matter have been considered.
The composition of the milk, its chemical charac-
teristics, the number and kind of bacteria con-
tained, the forms of adulteration which occur and
the methods for detecting such adulteration have
all been broadly covered. The relation of milk to
the public health and the disease epidemics which
have been due to infected milk have received large
attention in published works. Much has also been
published regarding the most effective methods to
be employed in the public control of milk supply. ©

While there is an extensive literature concern-
ing the problems of milk pasteurization dealing
with the matter from the theoretical side, and also
covering certain special phases of the work, it is
rather surprising to find how little of this is
available for the practical use of the milkman who

7

THE PASTEURIZATION OF MILK

wishes to install pasteurizing apparatus and to so
handle his output that the most efficient service
can be secured with the least possible expense.
This dearth of literature has been no doubt largely
due to the fact that the information which the
many practical men have gained in their experi-
ments has never been so brought together that it is
available for the use of those who are seeking
knowledge along practical lines. That this should
be so is but natural, for several reasons. .

First: The manufacturers who are interested in
emphasizing the good points of their apparatus
are not inclined to call attention to their defects.

Second: Milk dealers who, through experiments
in trying out various forms of apparatus have
learned what appears to be best suited to their
needs, are not inclined to publish to the world
information which has cost them much time and
money to secure. Should they do so, they would
be benefitting their competitors.

Third: Public officials in city, state or national
public service, who have made many inspections,
conducted tests and carried on extensive research
work are comparatively few. In fact, in very few
cities is the field for observation sufficiently exten-

8

FROM THE PRACTICAL VIEWPOINT

sive to enable such officials to draw unbiased or
broad conclusions. State officials are as yet doing
little work along these lines. The general govern-
ment has been and is now carrying on extensive
and valuable experimental work, and as a result
much useful and valuable information has been
published.*

The writer has published some matter which his
experience has taught him.t Dr. Rosenau has
devoted considerable space to the subject of milk
pasteurization and has given much valuable infor-
mation on the subject.

Additional information which is of considerable
value has been acquired by the experience of the
writer and other inspectors in the New York City
Department of Health, working in conjunction
with the laboratories. It seems to be proper that
this information could be available to the general
public.

As before stated, the application of heat to per-
ishable foods in order to preserve them from de-

*Ayers and Johnson, Bureau of Animal Industry—Circular
184 and other publications.

+N. Y.C. Department of Health Reprint Series Nos. 1 and 27.
tThe Milk Question by M. J. Rosenau.

9

THE PASTEURIZATION OF MILK

cay has probably been practised since the discov-
ery of fire. The earliest record of the application
of heat to food in a scientific way was in 1872,
when Sheele, the well-known Swedish chemist,
discovered that vinegar could be preserved against
spoiling by heating it. Soon after this other peo-
ple began to preserve fruits, vegetables, milk, etc.,
by heating them in closed vessels. No scientific ex-
planation, however, of the reason why the heating
process preserves these foods appeared until 1860
to 1870, when Pasteur, in his studies as to the
causes for the deterioration which took place in
wines and beers, discovered that there was certain
forms of life previously unknown whose unchecked
growth gave to liquor its bad flavors, ete. These
were termed by Pasteur “diseases.” He discovered
that by heating beer and wine to a temperature of
158° to 176° F., and holding the fluids at these
temperatures for a period of time, the “disease
germs,” as he called them, were destroyed and the
flavor of the liquor was improved, the loss by
spoiling being at the same time prevented.

This discovery was of immense financial benefit
to Europe, and in consequence the heating of wines
and beers became very generally practised, the

10

FROM THE PRACTICAL VIEWPOINT

See a ee eee aE al

process being termed “pasteurization,” from the
name of the man who originated it. At the present
time, no brewery is considered to be well equipped
and up to date unless extensive apparatus is em-
ployed to heat the product before it is placed upon
the market.

The thought that the same principle might be
applied to the preservation of milk on an exten-
sive scale had its birth in Europe, and it is claimed
that the first commercial milk pasteurizer was
made by Ahlborn in Hildeshein, Germany, in 1880,
and that a similar apparatus was made in the same
year by Fresca in Berlin, Germany. The process
was later adopted in Denmark, where dairying has
reached such a high degree of perfection.

At all events, the machine now known as the
Danish pasteurizer was introduced into this coun-
try by Reid about 1895, and is now sold under
various names by different manufacturers. Modi-
fications and developments of the original idea
form the basis of nearly all the pasteurizing ma-
chines used at the present time.

This form is illustrated in Figs. 1 and 2, and is
described more in detail later in this book.

In Denmark the object sought by the use of the

11

THE PASTEURIZATION OF MILK

pasteurizer was the improvement of the flavor and
quality of butter, the manufacture of which is such
an important industry in that country. The pas-
teurization of the cream used for butter is there
generally practised, and it is subsequently ripened
by the introduction of a pure culture grown in the
laboratories in order to secure the most desirable
texture and flavor. These methods have resulted
in the production of a butter in Denmark which is
considered to be a standard article. The indus-
try has grown remarkably and its products are
shipped to England and other parts of Europe in
normal times, and have also, in times of shortage,
. been shipped to the United States.

When it became appreciated in Denmark that
the spread of bovine tuberculosis was a danger-
ous menace to the dairy industry, a law was passed
requiring that milk whey, etc., which was fed to
calves, swine and other animals must be heated
before being fed in order to prevent the spread of
this disease among the growing stock. This
proved so useful in accomplishing its object, that
similar laws have been passed in various states in
this country. Vermont and Pennsylvania have
such laws in the East. Strange to say, many of

12

FROM THE PRACTICAL VIEWPOINT

the dairymen object to this, much preferring the
unheated skim milk. The dangers are not gen-
erally appreciated.

It became apparent to some people that that
which was good for preventing disease among cat-
tle would also be useful in preserving health
among children, and in 1866 Soxhlet advocated that
milk which was fed to infants be heated. About
this time, Jacobi, the distinguished American pedi-
atrist, advised the boiling of milk fed to infants.
In 1869 he referred to the apparatus devised by
Soxhlet, this being the first American reference
to the subject. This was before it was so well
known, as is now generally accepted, that milk is
a means of carrying infectious diseases, such as
diphtheria, typhoid, scarlet fever, etc. Jacobi found
that children fed upon boiled milk were less liable
to have intestinal disorders, and his long and con-
tinued success in treating children tends to dis-
credit the assertions made by some that the pas-
teurization of milk at comparatively low tempera-
tures destroys its nutritive value and is injurious
to children. Jacobi still advocates the boiling of
milk.

It was soon brought to the attention of milk

13

THE PASTEURIZATION OF MILK

dealers that milk which was old and liable to be-
come a commercial loss on account of souring
could be saved if it were heated, and that the fer-
mentation due to the growth of the enormous num-
ber of bacteria in milk could thus be checked.
Milk which had been handled in an unclean man-
ner, or which had been badly cooled by insuffi-
cient icing, or which it became necessary to hold
for a long time before sale, could still be made
marketable by rapidly heating and cooling it. Lit-
tle attention, however, was paid to the matter of a
uniform heating of the milk, or to the exact degree
of temperature to which it was subjected. Almost
no attention was directed to the destruction of
pathogenic bacteria. These, in fact, were little un-
derstood by the milk dealers, and few dealers main-
tained laboratories for studying milk problems.
On account of the questionable motives which
actuated dealers in adopting this method of milk
treatment, as well as the faulty methods employed,
health authorities, as a rule, at first looked upon
the pasteurization of milk with disfavor. It was
considered that the process was a makeshift and
simply used as a means of covering up bad prac-
tices in the production and handling of milk. In-

14

FROM THE PRACTICAL VIEWPOINT

stead of encouraging the pasturization of milk, or
even ignoring it, health authorities rather took
steps to discourage its practice. The desire to se-
cure a safe milk supply for the public took form
in strenuous efforts to clean up the sources from
which the milk was secured, to secure proper re-
frigeration and to assure clean handling. The cry
was for clean milk as produced from the dairies,
and the process of pasteurization was frowned
upon.

In New York and other cities, commendable
progress was made in the effort to secure a clean,
safe raw milk, and the improvement made in the
conditions under which milk is handled, particu-
larly in receiving stations and creameries, can
hardly be appreciated by those who were unfa-
miliar with conditions before the campaign for
clean milk was inaugurated. Dairy conditions
have also been greatly improved, and the dairymen
themselves repeatedly say that they would not for
any consideration go back to old conditions. All
efforts made to advance the production of clean
milk should be continued with unabated vigor.

It soon became apparent, however, that the se-
curing for a large city of a raw milk supply

15

THE PASTEURIZATION OF MILK

which could be guaranteed to be reasonably clean
and safe was practically impossible. If it was se-
cured, it would involve the expenditure of an enor-
mous amount of money and energy, which the tax-
payers would not approve, and it was seen that it
might result in so much added expense to pro-
ducers and dealers that the price of milk to the
consumer would be greatly increased, perhaps to
such an extent that the sale of this valuable uni-
versal food would be seriously curtailed.

Public health administrators were at length led
to the conclusion that the pasteurization of milk
was the only practical means of securing a sup-
ply which would be reasonably safeguarded against
dangerous infection. By many persons it was con-
sidered to be a makeshift, and it is still so re-
garded by some authorities, it being held by them
that its employment should only be continued until
a clean, safe raw supply can be secured. Others,
and by far the majority of authorities, are, how-
ever, convinced that pasteurization will always be
a necessity, and that even the best of raw milk
should be provided with the additional safeguard
which will be secured by pasteurization.

It is even urged by some that certified milk,

16

FROM THE PRACTICAL VIEWPOINT

which is the safest raw milk possible to be ob-
tained, should be pasteurized before being used for
infant feeding. This thought has been strength-
ened by information of comparatively recent dis-
covery, that milk may become infected through
coming in contact with persons who harbor dis-
ease germs, but who are not in any way ill. These
persons are therefore perfectly innocent of any
knowledge that they are a source of infection to
milk, and thus a dangerous and insidious menace
to the milk consumer. It has been found that cer-
tain persons may be, and not infrequently are, in-
fected with typhoid bacilli, without they themselves
knowing that they are thus infected. Such per-
sons are known as typhoid carriers. Other persons
harbor the germs of diphtheria in mouth and
throat, without having any symptoms of the dis-
ease whatever. Such persons may handle milk and
unwittingly infect it.

Within the last few years there have been in
different cities epidemics of septic sore throat.
These have occurred in Boston, Baltimore, Chi-
cago, ete. In Boston in 1911 several thousand
persons were made ill by milk coming from a
farm where the milk was exceptionally well cared

17

THE PASTEURIZATION OF MILK

for.* Many of the persons thus affected died.
In 1912 a similar epidemic occurred in Baltimore,
where many persons were made sick and many
deaths occurred. This was traced to milk infec-
tion.| Had these milks been properly pasteur-
ized, these epidemics of disease would probably
have been avoided.

Aside from the foregoing considerations, the
fact that a very considerable percentage of cows
producing milk are tuberculous gives an added
reason why it is desirable to heat the milk be-
fore use. There has been much misapprehension
in the public mind regarding the actual danger
which threatens human beings from this source.
There seems to be no doubt that these dangers,
while real, have been somewhat exaggerated. In
the first place, the fact that a cow may be seri-
ously affected with tuberculosis does not make it
certain that her milk is dangerous to use. If
proper care is exercised while the milk is being
drawn from the cow, none of the germs will get

*Winslow, C. E. A., Journal of Infectious Diseases, Volume X
No. 1, January, 1912.
{Public Health Reports, November 22, 1912.

18

FROM THE PRACTICAL VIEWPOINT

into the milk. Of course, if the disease existed in the
udder of the cow, or in the milk ducts, there would
then be direct contamination of the milk as it was
drawn. Cows more frequently, however, have the
_ disease in the lungs or other parts of the body, in
which case the germs will pass through the alimen-
tary tract and be voided with the urine and feces.
If the cows are allowed to become badly soiled,
particles of manure and dirt, carrying with them
the tubercle bacilli, will inevitably fall into the
milk, thus infecting it. It is also possible that
dried manure in stables where tubercular cattle
are kept will produce dust, which, when stirred
up by the movements of the cattle or by persons
and by sweeping, may fall into the milk. This
danger is probably more imaginary than real,
since recent experiments by the Geneva Experi-
ment Station * indicate that stable dust plays a
part in milk infection which is of comparatively
little importance. It is also true that the exposure
of manure to light and air for a length of time
sufficient to produce a dry dust would tend to de-
stroy the tubercle bacilli. The amount of infec-

*Bul. 409. N. Y. Ag. Exp. Sta.
19

THE PASTEURIZATION OF MILK

tion would be therefore comparatively small. It
is also a known fact that while tubercle bacilli will
live in milk, they will not multiply.

The apprehension experienced by many persons
that they may be infected with tuberculosis from
the milk which they consume should be lessened
by their knowledge of this further fact, namely,
that tuberculosis of the bovine type with which
cattle are affected is rarely infectious to human
beings who are over fifteen years of age, and
rarely causes fatal tuberculosis in children over
five years old. The careful examination of hun-
dreds of cases where death has occurred from
tuberculosis among children appears to conclu-
sively show that the danger of infection from bo-
vine tuberculosis is largely limited to persons
under fifteen years of age. Of deaths from tuber-
culous affections of persons under this age, only
10 per cent. had tuberculosis of the bovine type.
This has been determined for New York City by
investigations carried on by Park and his col-
leagues, extending over several years, and the same
conclusions have been reached by European sci-
entists.

The records of New York City for the years

20

FROM THE PRACTICAL VIEWPOINT |

1913-1914-1915 show the following interesting
facts:

DeratHs or CHILDREN UNDER FIFTEEN YEARS.

1913 1914 1915
From all causes... 23,574 22,312 23,031
From all tubercular 7
diseases ....... 1,288 1,166 1,200
10 per cent of these
latter figures in-
GMS ese oS . 128.8 116.6 120.

These represent the number of persons who died
in these years from tuberculosis which was prob-
ably of bovine type.

This means that out of every 1,000 deaths from
all causes of children under fifteen years of age,
5.4 in 1913, 4.8 in 1914, and 5.2 in 1915, had
tuberculosis which was probably of the bovine
type.

While it is possible that bovine tuberculosis may
reach human beings through infected meat or by
direct infection from dust, dirt, ete., it is probable
that most of it is due to infected milk.

There are many cases of tuberculosis existing

21

THE PASTEURIZATION OF MILK

in bones and glands which do not result fatally.
Nearly one-half of these are thought to be of the
bovine type, and very likely have their origin in
milk.

It is evident, therefore, that while the danger of
tubercular infection from milk when expressed in
terms of percentages is comparatively slight, there
appears to be, nevertheless, a definite danger to
children from this source, and the safeguarding of
this milk by pasteurization is extremely desirable.

Rosenau * places tuberculosis first among the
diseases carried by milk, thus considering it a
greater menace than typhoid fever.

All these facts have induced most health authori-
ties to change their attitude toward the pasteuriz-
ing of milk for general use, and it is now the ex-
ception instead of the rule to find persons familiar
with the subject who favor the use of raw milk,
except when it is from dairies which are abso-
lutely above suspicion.

The important consideration which influences
authorities when they insist that milk be pasteur-
ized is of course the desire that the milk may be
free from dangerous bacteria.

*The Milk Question—M. J. Rosenau.
oo

FROM THE PRACTICAL VIEWPOINT

There are commercial reasons which influence
dealers, such as the desire to prevent the souring,
and thus the loss of milk, but these considerations
have little weight with health authorities. The
prevention of economic waste of food products has
a bearing upon the public health, and there are
indications that the personal interest which those
in authority have as men in these matters is being
extended to their official interest. Care must be
observed, however, that these two considerations be
justly balanced.

The United States Government has endeavored
to reduce the losses which result from the condem-
nation of cream which is not considered fit to use
as cream. This is accomplished by partially de-
naturing it by the addition of salt, so that it can be
used for butter making. An attempt has also been
made to prevent the destruction of milk which has
a temperature above that fixed by the authorities
as legal. It is well known that in some cities this
drastic action is taken in order to secure proper
refrigeration. Such destruction of milk, which has
a high food value, should be looked upon as almost
criminal,

Careful experiments carried on by Park, Rose-

23

THE PASTEURIZATION OF MILK

nau, and others have demonstrated the fact that
if milk is heated to a temperature of 140° F., and
is held at this temperature for twenty minutes, or
even less, all of the pathogenic or disease-produc-
ing bacteria will be destroyed. Also, if the milk
is heated to a uniform temperature of 158° F.,
and held thereat for one minute, all such disease
germs will be killed. Between these extremes, dif-
ferent degrees of temperature, and correspond-
ingly varying lengths of holding time, will pro-
duce equally good results. These experiments
have been carried on of course in laboratories
where ideal conditions for securing accurate re-
sults existed. Accurate temperatures could be ob-
tained and the length of time for which the milk
was held could be carefully controlled. When,
however, pasteurization is carried on under com-
mercial conditions, where large quantities of milk
are handled, the same amount of accuracy is not
possible. There are variations in temperature and
variations in the length of time for which it is
held, due largely to the mechanical defects or
limitations in all forms of machinery. These fac-
tors of error render the results uncertain, and it
is therefore desirable that the temperatures and

24

FROM THE PRACTICAL VIEWPOINT |

the lengths of time for holding, which in the labo-
ratory tests have been found to be effective, be
somewhat increased, in commercial practice.
Various cities have made regulations in this re-
spect which appear to best suit local conditions.
In New York City, when regulations were first
adopted concerning milk pasteurization, the length
of time for which milk must be held when heated
to 158° F. was officially fixed at no less than three
minutes, and if heated to 140° it must be held for
at least twenty minutes. Between these extremes
of temperature holding times were fixed which va-
ried between three minutes and twenty minutes.
Experiments were made by Schores and Rose-
nau * in which careful tests were carried on while
milk was being pasteurized in the ordinary way,
a commercial pasteurizer and holding device being
used. These tests were made for the purpose of
determining if the thermal death point of patho-
genic bacteria, as indicated by laboratory tests,
could be safely relied upon under commercial con-
ditions. In their experiments the investigators in-
troduced germs of tuberculosis, diphtheria, and
typhoid fever, into milk, which was then run

*The Journal of Medical Research Vol. XX VI No. 1.
35

THE PASTEURIZATION OF MILK

through a commercial pasteurizer and heated to
different temperatures, and held for varying lengths
of time. The results obtained indicated that when
an attempt was made to heat this milk in a com-
mercial pasteurizer to a temperature of 140° F., and
then hold it for twenty minutes, there was a con-
siderable unavoidable variation in the actual tem-
perature to which the machine was capable of
heating the milk. This was due to the difficulties
of both hand and automatic temperature control.
Even with the best automatic controller, it is
probable that the real variation of temperature is
greater than is indicated upon the record charts.
Thermometers are not usually sufficiently sensitive
to record rapid fluctuations in temperature. It is
also true that thermometers indicate average tem-
peratures only, and it is possible that certain por-
tions of the milk, the temperature of which is con-
siderably below this indicated average, pass
through the apparatus.

In regard to the time held also, especially when
a continuous or flow type holding apparatus is
used, great uncertainty exists. It is impossible to
be sure that the time is the same as intended. The
rate of flow varies, and there is also more or less

26

FROM THE PRACTICAL VIEWPOINT .

mixing of the milk due to various causes, which
will be discussed later.

Schores and Rosenau found that pathogenic bac-
teria were not all killed when the factors of tem-
perature and time were attempted which had been
found effective in laboratory tests. They there-
fore recommended, in order to provide a sufficient
margin of safety, that all milk he heated to a
temperature of at least 145°, and there held for
no less than twenty-five minutes. This opinion is
shared by most persons who have made a study
of the subject. The New York City Department
of Health, in 1914, so modified its regulations as
to require that pasteurized milk be heated to from
142° to 145° F. for at least thirty minutes.

While the destruction of all pathogenic bac-
teria in milk is the primary concern of health au-
thorities, there are certain other considerations
which have weight with them, and among these
is the effect which heat has upon the chemical
characteristics of the milk. It has been found that
when milk is heated to say 160° F. or over, some
of the constituent parts of the milk are changed in
such a way as to make it somewhat inferior as a
food, especially for infants. These changes have

27

THE PASTEURIZATION OF MILK

been somewhat extensively studied by the United
States Government experts, and it has been found
that as the temperature rises above 160° F., these
changes take place to an increasing extent, and at
the boiling point quite extensive changes are ob-
served. At this temperature, the milk sugar be-
comes scorched, the casein and the albumin are
somewhat hardened, the calcium, magnesium and
phosphoric salts are partially precipitated, all of
which renders the milk less easily digested. It
therefore follows that the lowest temperature
which is consistent with the destruction of the
pathogenic bacteria is the most desirable.

It is also true that milk which contains an ex-
cessive number of bacteria carries with it, as a re-
sult of their growth, certain by-products, such as
acids and other undesirable substances, and may
also contain dangerous poisons. Rosenau states
that the known poisons which are produced by the
growth of bacteria in milk are very few, but that
such poisons may possibly exist and produce harm-
ful effects upon the persons using the milk. These
by-products of bacterial growth in milk are not
entirely destroyed by heating, even when the boil-
ing temperature is attained. For this reason it is

28

FROM THE PRACTICAL VIEWPOINT

desirable that milk which is to be pasteurized shall,
before it is heated, be as free as possible from all
bacteria. It is this consideration which has led
health authorities to insist that the milk before pas-
teurization shall not contain an excessive number
of bacteria. .

Milk dealers know that their customers com-
monly judge of the richness of the milk by the
amount of cream which appears upon the top of
the bottle. For this reason the showing of a
“good cream line” is one of the things for which
the milk dealer strives. In some parts of Europe
the cream is thoroughly mixed in the milk by
homogenizing it, so that the cream will not rise,
but the American housewife is not educated to this
custom, and therefore anything which interferes
with the apparent volume of cream on the milk is
a stumbling-block to the milk dealer. It has been
found that milk which is heated to a temperature
of 148° F. or over and is held for any consid-
erable period of time, will have its cream line de-
stroyed, or at least be made indistinct. When
milk is heated to a temperature lower than this
and is held for a great length of time, the same
effect is produced. There are other reasons which

29

THE PASTEURIZATION OF MILK

interfere with the cream line which will be dis-
cussed later.

Another objection which customers urge against
pasteurized milk is that it has a distinctly
scorched or cooked taste. This is undoubtedly true
when the milk is heated to a high temperature, or
when an uneven temperature is maintained. If the
heating medium is kept at a point greatly above
the temperature to which the milk is to be raised,
the same effect is produced. On account of this
cooked taste it is evident that there is a commer-
cial objection to pasteurization where it is not
properly or carefully done.

. Moreover, when a low temperature of heating is

used, the enzymes are not much affected, while
they are destroyed when a high temperature is ap-
plied. Indeed, the Storch test, which is used to
determine whether skim milk has been heated to
165° or higher in compliance with the laws in this
regard, depends upon the non-action of the en-
zymes. These are destroyed by high heating.
This test is of little or no value in testing milk
pasteurized at low temperature.

Since an even heating at comparatively low
temperatures and a holding for a long time secures

30

FROM THE PRACTICAL VIEWPOINT

the desired result in the destruction of bacteria,
and at the same time produces none of the unde-
sirable effects which follow when. a high tem-
perature is employed, it is evident that this
method of procedure is that which is much to be
preferred.

To summarize the danmideraaons which have
just been discussed, it is evident that the pastur-
ized milk which most nearly fulfills the require-
ments desired by health authorities, and at the
same presents, from the commercial aspect, the
least objections, must conform to the following de-
mands:

First: Before pasteurization it must contain only
a small number of bacteria.

Second: When it is heated it must be subjected
to a temperature which destroys all pathogenic or
disease-producing bacteria, and also a large per-
centage of bacteria of all other kinds.

Third: Its constituents must be very little
changed or altered by excessive heating. Its nu-
tritive value must not be impaired, and its diges-
tive enzymes must be uninjured.

Fourth: The taste of the milk must not be no-
ticeably changed.

31

THE PASTEURIZATION OF MILK

Fifth: The apparent volume of cream must not
be reduced.

In so far as these factors represent results
which are properly demanded by health authori-
ties, there are, broadly speaking, two general
methods by which they can be controlled when
their control depends upon the powers exercised
by the municipality or the state. One of these
may be called the laboratory method, and the
other the inspectional method. When the labora-
tory method is employed it is necessary that cer-
tain definite chemical and bacteriological standards
be adopted, which apply to pasteurized milk or to
milk which is to be pasteurized. Some of these
standards may depend upon color reactions. Such
standards being in force, the effectiveness of con-
trol depends upon the frequent examination of sam-
ples of milk taken before and during the process
of pasteurization and as it is offered for sale. If
the tests show that the milk conforms to the legal
standards, it may be judged, with a fair degree of
confidence, that the apparatus employed in pas-
teurizing and handling the milk is properly in-
stalled and operated.

When the inspectional method of control is em-

32

FROM THE PRACTICAL VIEWPOINT

ployed, it is necessary that certain definite regula-
tions be adopted which shall specify on broad lines
the form of apparatus which must be used, how
it shall be installed and how it shall be operated.
The construction and arrangement of the build-
ings and of the various rooms may be specified, it
having been determined by previous experience
that such and such apparatus and surroundings
operated and handled in such and such a way will
produce milk which will be of the character de-
sired. With these regulations in force, it is pos-
sible, by frequent and careful inspections made of
pasteurizing plants, to determine whether or not
the legal regulations are being faithfully observed.
If it is found that they are complied with, then it
is logical and safe to conclude that the milk pro-
duced is of suitable character, and will satisfac-
torily respond to all suitable chemical and bac-
teriological tests which may be applied.

As a matter of fact, neither method of control
is used by authorities to the exclusion of the other,
but a combination of the two methods is found to
be the most satisfactory. In some cities the em-
phasis is placed upon laboratory tests, with in-
spections made to confirm the results. In other

33

THE PASTEURIZATION OF MILK

places, the emphasis is upon physical regulations
and inspections, with occasional laboratory tests to
confirm the conclusions reached and to aid in the
discovery of obscure defects which may escape ob-
servation during the usual inspections. No advice
can be given as to which method is most desirable
without first knowing local conditions, taking into
account the extent of the milk industry, the avail-
able factors of men, money and laboratory equip-
ment, etc. Each community presents its individ-
ual problem.

Health authorities are often requested by milk
dealers to give advice as to the form of pasteurizing
apparatus which will perform the best work, or
they are asked what kind of machine the authorities
recommend. It is manifestly improper for health
authorities to recommend specifically any one or
more forms of apparatus as the best. If they did,
they would lay themselves open to the charge of
unfair favoritism, and to the suspicion that im-
proper influence determined their judgment. It
is only proper that they should state that in their
experience certain forms of apparatus, operated
in certain ways, have performed certain things in
actual practice which are or are not satisfactory

34

FROM THE PRACTICAL VIEWPOINT

to those who are responsible for this condition of
the milk. Indeed, when advice is asked as to the
form of apparatus most desirable to be installed
at a given point, it is impossible to solve such a
problem without possessing complete knowledge of
the conditions which surround each plant where it
is desired to install a pasteurizer. Each plant
presents an individual problem of its own, which
must be carefully studied, having clearly in mind
all the facts which specially relate to the plant in
question. It is impossible to place too much em-
phasis upon this point, since time and money and
the securing of expert advice before the construc-
tion and equipment of a plant will frequently bring
continuous dividends in convenience, in the saving
of time, in preventing needless waste of money,
and in the general satisfaction which accompanies
the successful operation of an efficient plant.
Among the factors to be considered, the con-
struction and physical characteristics of the build-
ing where the plant is to be located is of impor-
tance in determining the selection of the appara-
tus to be used. Again, the distance of the plant
from the point where the milk is to be distributed
and consumed should be considered. If located

35

THE PASTEURIZATION OF MILK

in the country at a distance from the city, the ele-
ment of time available after the milk is delivered
by the dairyman is also an important item. The
amount of milk to be pasturized daily, and the
use which is to be made of the finished product
have a bearing upon the final decision. With
many dealers the question of expense may be of
first importance, but it must be borne in mind
that cheap installation does not always mean econ-
omy. The question of expense involves both the
initial cost of installation and the outlay for oper-
ation and upkeep. Where the matter of furnish-
ing sufficient steam is a point for serious con-
sideration, or where water expense affects the final
cost, it is desirable to use those forms of appara-
tus which consume the fewest heat units and which
use the least amount of water. ‘There are also
other considerations which will be discussed later,
and it will be found that at many plants unique
conditions exist which must be carefully studied.
On broad lines, however, it may be stated that
a pasteurizing plant, in order to be as nearly as
possible ideal in regard to its construction, and
which will at the same time be capable of produc-
ing a milk which will be satisfactory from the

36

FROM THE PRACTICAL VIEWPOINT |

standpoint of safety and wholesomeness, and will
also satisfy commercial demands, should combine
the following features:

1. The Building.—The building where the plant
is located should contain ample space and should,
if possible, be so arranged that the milk will flow
by gravity from the point of receipt, or where
cans are emptied to the point where it is taken out
for delivery or transportation.

2. Separate Rooms.—The various stages in the
process of treating the milk, such as receiving,
pasteurizing, cooling, filling containers, storage
and of washing the containers, should be carried
on in separate, clean, well-lighted and ventilated
rooms or compartments.

3. Protection from Contamination. — At all
points during the process of handling, the milk
should be protected against contamination from
contact with unclean apparatus, and from infec-
tion by means of dust-laden air. This protection
is especially necessary after the holding process
is completed. Any infection occurring after this
time is not corrected by heating, and may there-
fore be a source of danger.

4. Constant Temperature—The heating appa-

87

THE PASTEURIZATION OF MILK

ratus, whatever its form, should be capable of
heating every particle of milk to a temperature
which will never be below that to which it is the
intention that it shall be heated. For instance,
if it is intended to heat to 140°, the temperature
should not fluctuate between 135° and 145°, but
should remain constantly at 140° or over.

5. Method of Heating.—The heating should be
accomplished by an apparatus which allows the
milk to flow over a clean metal surface, which is
kept hot by means of heated water, and not by
direct steam contact. This hot water should never
have a temperature more than 10° or 15° higher
than that to which it is desired to heat the milk.

6. Holding Apparatus——The holding appara-
tus, whether the absolute or the continuous flow
type process is employed, should be so constructed
and operated that it will definitely insure the
holding of every particle of the milk without fail
for the desired length of time.

7. Recorders—The temperature to which the
milk is heated must be automatically recorded, and
should be automatically controlled. It is desir-
able that a temperature recording device be in-
stalled at the point where the milk leaves the

38

FROM THE PRACTICAL VIEWPOINT |

heating apparatus and that another recorder be
attached to the outlet pipe from the holder. This
latter recorder indicates whether or not any great
amount of heat has been lost during the holding
process, and also shows whether the apparatus is
thoroughly heated before the milk is admitted. If
not so heated, the first milk leaving the holder
will have been somewhat cooled, and the recorder
will indicate this. After the apparatus has been
in operation for a considerable time, it will then
acquire the temperature of the milk, which will
then pass out with the temperature but little di-
minished. These observations do not apply to a
tank or batch pasteurizer. In this case a single
recorder attached to the tank itself shows all that
is necessary. It also indicates the time for which
the milk is held at the required temperature.

8. Pumps and Pipings.—The amount of milk
piping in use should be reduced to the minimum
requirements. All piping which is used should
be of sanitary construction, with the joints and
turns so arranged that they can be easily taken
apart for cleaning. As before stated, the appara-
tus should be so arranged that the milk will flow
by gravity from point to point in the process of

89

THE PASTEURIZATION OF MILK

treatment. If, however, it is necessary to use milk
pumps, they should be of absolutely sanitary con-
struction. The use of pumps for moving the raw
milk is less objectionable than is their use for mov-
ing pasteurized milk. Not only is the danger of
infection by means of unclean pumps very serious,
but if the milk is pumped while hot, the cream is
so disturbed that it does not rise as readily as is
desirable.

9. Rubber Fittings and Gaskets——The use of
rubber fittings, of gaskets and of stuffing-boxes
should be avoided.

10. Cooling.—The milk should be immediately
and rapidly cooled, to a temperature as nearly
40° F. as possible. This cooling should be accom-
plished within thirty minutes after the heating and
holding process is completed. Except where cool-
ing is carried on in the tanks where it is heated,
the cooling can be completed in much less than
thirty minutes. The milk should be, of course,
kept cold until delivered to the consumer.

11. Cleaning of Containers—All containers,
including cans, covers and bottles, should be com-
pletely and if possible automatically washed and
sterilized. They should then be thoroughly dried

40

FROM THE PRACTICAL VIEWPOINT

and should be stored in clean, cold rooms, and there
kept inverted or carefully covered until filled.

12. Cleaning of Apparatus.——All apparatus
used in handling milk should be carefully washed
and sterilized after its use, and all of it which
comes in contact with the pasteurized product
should be again sterilized before its use each day.

13. Healthy Employees.—All persons employed
in handling the milk should be known to be healthy
and free from any infectious disease. They
should be clean in their person and habits, and
should wear special clean clothing, preferably of
white material, while handling milk.

14. Bottle Capping—The milk bottles, after
filling, should be capped by clean machinery, thus
avoiding as far as possible any personal contact
with the milk after it is pasteurized.

It is needless to say that all the ordinary precau-
tions regarding the sanitary construction of build-
ings where food is handled should be observed,
and the close proximity of stables or other con-
taminating influences should be avoided.

There are, of course, many other points of de-
tail in the construction and operation of pasteur-
izing plants which will repay careful attention.

41

THE PASTEURIZATION OF MILK

These will be touched upon in the following pages.
On broad lines, however, it may be said that if the
foregoing conditions are carefully fulfilled, then
it will be possible to obtain a good safe milk which
the public may consume with a feeling of security,
and which should satisfy all eiemE of health
authorities.

It is not proper, of course, to recommend any
specific type or form of apparatus to be used in
pasteurizing milk. It is proposed, however, to de-
scribe in the following pages and to show by dia-
gram or illustration the construction and operation
of different makes of apparatus, and to call atten-
tion to those points in each which experience has
taught are of advantage or disadvantage.

42

CHAPTER II
HEATERS

In 1909 the New York City Department of
Health first adopted the rule which required that
milk could not be considered as pasteurized un-
less it had been heated to a definite temperature
and held at this temperature for a certain definite
length of time. New York was the pioneer in
requirements of this sort.

At this time various forms of milk heaters were
on the market, but no device was available for
holding the heated milk. All heaters employed
a process which is known as the continuous or flash
process of heating. By this process the milk
flowed or was forced in a continuous stream
through the apparatus, where it was subjected to
an amount of heat which was not very definite, and
which was controlled by the hand of the operator.
The milk was then immediately cooled.

Most of the forms of apparatus which were
then on the market are still in use, and certain new
forms of heaters have been invented. Certain new
types of apparatus were devised as adjuncts of

43

THE PASTEURIZATION OF MILK

the heaters, into which the milk was allowed to
flow from the heaters and in which the hot milk
was held for the time required by the regulations.

As before stated, the forms of heaters in use
in 1909 are still employed, with certain new forms
made by many different manufacturers. They are
all comprised under some one of five typical forms,
as follows:

First Type—The so-called Danish heater is
sold by various firms. It is shown in the accom-
panying illustrations (Figs. 1 and 2). This is
the oldest form of heater in use in this country.
In this form a large central cylinder is provided
with a double cover or jacket. The space between
the inner and outer shell is filled with water, into
which steam is introduced. By means of a
suitable device the steam is distributed through the
water at various points.

In operation, the milk is allowed to flow or is
pumped into the inner compartment or cylinder,
and by means of rapidly revolving paddles it is
thrown by centrifugal force against the inner sur-
face of the cylinder. This surface is kept hot by
means of the hot water and steam in the outer
shell. The milk enters at the bottom of the cylin-

44,

FROM THE PRACTICAL VIEWPOINT

Fic. 1 ‘Fic. 2

der, and since the outlet pipe at the top is placed
at a tangent to the cylinder, the rotating paddles
tend to throw the milk out of the pipe. The ma-
chine therefore acts somewhat as a pump, and
when the whole machine is set at an angle from
the perpendicular, this tendency to throw the milk
is enhanced and the milk can be lifted about fifteen
feet. This fact is one of the advantages of the
machine. Another advantage is that it is com-
paratively inexpensive, since it is rather small. Its

45

THE PASTEURIZATION OF MILK

size also tends toward the ease of cleaning, there
being no great amount of surface with which the
milk comes in contact.

This very fact, however, that the heating sur-
face is small in area, is also a disadvantage, for
it renders it necessary to raise the temperature of
the heating medium to a point so high that it is
frequently very much in excess of that to which
it is the desire to heat the milk. The result is
that certain portions of the milk reach a tempera-
ture so high that a distinctly scorched taste is im-
parted to it. This taste persists in the entire
body of the treated milk, even though the average
temperature of the milk leaving the apparatus is
below 145°. This is especially noticeable if the
flow of milk into the apparatus fluctuates. It can
be readily seen that with a very hot heating sur-
face, and at the same time a small amount of milk
passing through the machine due to a sudden stop-
page of flow, this milk would attain a high tem-
perature.

This superheating of even a portion of the milk
tends to cause an interference with the normal
rising of the cream, after the milk is placed in
containers. The vigorous agitation of the hot milk

46

FROM THE PRACTICAL VIEWPOINT

by means of the paddles also has a tendency to
break up the fat globules into smaller particles,
which do not so readily rise to the surface.

It is difficult to maintain a uniform temperature
with this type of machine, since the amount of
heating fiuid is comparatively small, and when
there is either a fluctuating flow of milk or a vary-
ing milk temperature, there is no automatic con-
troller which can be made to respond to sudden
changes in temperature quickly enough to check
or increase the flow of steam into the heating
chamber.

As a general proposition, also, the introduction
of steam directly into a heating chamber is to be
avoided, since there is always the possibility that
certain portions of the steam will strike the heat-
ing surface before becoming condensed, and will
therefore heat these portions to an abnormally
high point.

Second Type.—There are several heating de-
vices made by different firms, and having certain
variations in the details of their construction,
which embody the same general principles. These
are illustrated in Figs. 3, 4, 5. In all of these
the milk flows between two or more upright, heated

A'7

THE PASTEURIZATION OF MILK

HUTS

?)
a Fe EE

Fie. 3

1—Discharge of warmed milk to gathering tank.
2—Return of warmed milk to interior of heater.
3—Discharge of heated milk to holder.

4—Hot water intake.

5—Return of held milk to regenerator.

6—Cold milk entering heater.

7—Discharge of partly cooled miik to cooler.

48

FROM THE PRACTICAL VIEWPOINT

THE PASTEURIZATION OF MILK

Fie. 4-B

cylindrical surfaces. The heating surfaces are
kept at the desired temperature by means of hot
water, which in turn is heated either by the intro-
duction of steam into the water chamber directly,
or by heating the water in tanks outside the milk

50

FROM THE PRACTICAL VIEWPOINT

== isla

Ave

WN

AGN ASATINAANANNN AN ANNAN
—e4

vs Pat
es
s

: a | i)

vy a = E
i 7A _iok hs
WLLL
aegis:

Fig. 5
1—Interior water tank.
ti

2—Exterior water tank. : ‘
3—Space between water tanks, through which milk is forced upward.

THE PASTEURIZATION OF MILK

apparatus. From these tanks it is pumped into
the heating chambers. Where steam enters di-
rectly into the milk apparatus the same objections
obtain which were noticed in the description of the
Danish type of heater. Superheating of the milk
in whole or in part, an objectionable cooked taste,
interference with the cream line, etc., are likely to
follow. Where an outside heating tank is employed,
it is comparatively easy to keep the water at a
nearly uniform temperture by means of a thermo-
stat, which controls the introduction of steam.
With this heated water being pumped to the milk-
heating apparatus, it is certain that the milk can
never get above the temperature to which the water
is heated, and if this water is not more than 10° or
15° hotter than the temperature at which it is the
intention to heat the milk, no serious superheating
can result. This point will be more fully de-
scribed later.

In all heaters of this type some method is em-
ployed to keep the milk in constant motion as it
flows upward between the heating surfaces, thus
insuring that all portions of milk come in contact
with their surfaces. In the machine illustrated in
Fig. 3 this agitation is accomplished by means of

52

FROM THE PRACTICAL VIEWPOINT |

a revolving arm, which extends into the milk space
between the inner and the outer water chambers.
In Fig. 5, the inner cylinder revolves and the nar-
row corrugation which extends in a spiral form
around the cylinder forces the milk upward. The
shaft which operates these stirring devices in some
instances comes in contact with the milk, and in
order to prevent leakage, it is necessary to pro-
vide some sort of packing or stuffing box. This
is a disadvantage, since nearly all packing is some-
what porous, and it is difficult to keep clean.

Heaters constructed in this general form have
been found to be effective in operation, and good
results have been obtained by their use. They
have been found to be durable as well. Some in-
dividual machines have been in use for ten years,
which indicates the carefulness with which they
have been constructed. Those forms of heaters
are the most satisfactory in which the greatest
amount of heating surface is available, and where
the amount of hot water which circulates through
the apparatus is relatively large. These conditions
render it possible to use water which has a com-
paratively low temperature.

Some of these heaters employ what is known

53

THE PASTEURIZATION OF MILK

as the “regenerative principle.” ‘This means that
the hot milk which flows from the machine is em-
ployed for warming the cold milk which flows into
the apparatus to be heated. When this regenera-
tive principle is used, a considerable economic sav-
ing of heat units is secured. This saving means _
that less steam is required for heating, and also that
less ice is necessary for cooling. In the type illus-
trated in Fig. 4 the milk flowing from the holder
is conveyed to a holding apparatus, and after be-
ing held is returned to the heater, where it flows
through another compartment and helps to heat
the inflowing cold milk.

At least one form of regenerative heater (Fig.
6) is so constructed that this intermediate holding
process cannot be used. In sections of the country,
therefore, where city regulations require that the
heated milk be held for a definite period, this form
of heater cannot be used. As a so-called “flash”
pasteurizer, this machine has given good results.

In Fig. 4-B is shown a form of heater in which
the hot water is contained on the inside of the lower
cone. The milk flows from the top over the heated
cone. Revolving arms to which is attached a heavy
cord, keep the cone surface wiped, and prevent

54

FROM THE PRACTICAL VIEWPOINT |

9 “SIT

55

THE PASTEURIZATION OF MILK

the milk from sticking to the heated surface.
There is difficulty in keeping the cord clean and
sanitary.

Third Type—The tubular type of heater is
manufactured and sold by several concerns. In
all of these forms, the milk flows through tubes,
which are themselves surrounded by some heating
medium, usually hot water. In the form shown
in Fig. 7 the milk tube is enclosed by a larger
tube, through which hot water flows in a direction
opposite to the milk flow. In forms which are
illustrated by Figs. 8, 9 and 10 the heating water
is contained in boiler-like structures, through
which the tubes extend. Care must be exercised
in order to make sure that there can be no leak-
age between the milk tubes and the water con-
tainers. In Fig. 7 the couplings between the vari-
ous milk pipes in the series are outside of and
beyond the water couplings, so that no mixing of
the milk and water can occur unless there is a
broken milk pipe. In Figs. 8, 9 and 10 the milk
tubes are either braized or expanded into the heads,
and the danger of leakage is slight. Of course,
when heat is applied to these tubes, the tendency
is for them to expand and so become more tightly

56

FROM THE PRACTICAL VIEWPOINT.

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fixed in the heads. Sudden and wide variations of
temperature would tend to loosen the joints. The
flowage of the water in a direction opposite to milk
flow brings the hottest water against those milk
tubes where the hottest milk is found. As the

57

THE PASTEURIZATION OF MILK

Fic. 8

water flows along the tubes it becomes gradually
cooled by the cooler milk, so that it emerges at a
low temperature. Thus the milk is heated grad-
ually, and no sudden raising of the temperature
occurs. This renders the control of the tempera-
ture an easy matter, since sudden fluctuation in
temperature cannot readily occur. There is also

58

FROM THE PRACTICAL VIEWPOINT |

Fic. 9

an economical use of the heat, and little of it is
wasted.

In Fig. 11 a form of heater is illustrated in
which the milk flows through a group of small
tubes, which are themselves enclosed in a large

59

OF MILK

THE PASTEURIZATION

60

FROM THE PRACTICAL VIEWPOINT |

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THE PASTEURIZATION OF MILK

tube. The larger tube contains the water which
surrounds the small tubes which contain the milk.
When the regenerative principle referred to is em-
ployed, in this type of heater the hot milk return-
ing from the holding tanks is allowed to flow
through the larger tube, and thus assist in heating
the cold inflowing milk. .

Tubular heaters are doing very satisfactory
work. Those machines are in some respects the
most efficient in which the flow of milk is slow
enough or which have a sufficient heating surface
to insure that all portions of the milk will reach
the maximum temperature. It has been found
from experience that when milk flows through
tubes which are of comparatively large diameter,
there is a tendency for that portion of the milk
which is in the center of the tube to flow faster
than that which is close to the inner surface of
the tube. This is due to the greater friction at
the point of contact. It can be readily seen that
there will therefore be a tendency for the milk
which flows more slowly close to the heated surface
of the tube to become heated to a considerably
higher point than that near the center. When
the water entering the final tube of the heater is

62

FROM THE PRACTICAL VIEWPOINT

high in temperature, there is a certain amount of
danger of cooking or scorching the milk, and pos-
sibly of breaking up the fat globules. It is also
true that if a coating of cooked milk forms on the
inner surface of the tube, it acts as an insulating
material and therefore a constantly increasing tem-
perature must be applied to the water. The return
of the milk from one tube to another in the series
tends to mix the milk and so break up the more
rapid flowing core. This breaking up process,
however, may have a detrimental effect upon the
fat content and may render the cream less likely
to rise. In one or two instances known to the
writer it was found that when the milk left the
apparatus at a temperature of only 140° the cream
line was considerably interfered with.

The types shown in Figs. 7, 10 and 11 have this
advantage, namely, that since they can be obtained
in sections, the pasteurizing plant can be expanded
by the installation of additional sections as the
growth of the business demands. Since a cooling
apparatus of exactly similar form is provided it is
possible to extend the cooling facilities in the same
way. By a proper interchange of the water used
in both the heater and cooler, the regenerative

63

THE PASTEURIZATION OF MILK

principle is made use of, and the cool water leav-
ing the heater is carried over to the cooler, so that
it helps to cool the hot milk flowing into it.

In choosing a machine of this type, care should
be exercised in securing one which may be easily
cleaned, especially at the turns and joints. All
these should be smooth and readily accessible.

It should be borne in mind that while a large
heating area with many pipes is an advantage in
securing an even heating with a low water tem-
perature, the difficulties of cleaning are also in-
creased.

It is also readily seen that when powerful pumps
force the hot water rapidly through the heating
pipes, a relatively lower heating temperature may
be employed.

An objection to the tubular form of heater lies
in the fact that the tubes in this system are nearly
‘horizontal and parallel. There is thus but little
inclination or pitch to the tubes, and the milk flows
from them rather slowly when they are emptied at
the close of operations for the day. This objec-
tion has been overcome in some of the more re-
cently manufactured machines, by putting the
pipes at an incline and not parallel to each other.

64

FROM THE PRACTICAL VIEWPOINT.

Thus the milk can be more readily drained from
the apparatus when it is being emptied.

One striking advantage of the tubular type of
apparatus is found in the fact that it may be very
thoroughly sterilized. Steam can be admitted into
all the parts where the milk will enter, and the
steam may be under pressure if so desired.

It is important that a machine of this type be
so constructed that no milk will leak from one
section of tubing into another section, but that it
all follows the course which it is intended that it
shall follow. In the forms shown in Figs. 8, 9
and 10, the doors at the ends which cover the ends
of the milk tubes are provided with gaskets to
prevent this leakage.

It is well to note whether or not these gaskets
are tight. In one or two forms, the gaskets con-
sist of sheets of metal which are backed by felt
or rubber in such a way that the metal readily
conforms to the projections of the tubes, thus mak-
ing a closely fitting cover. The metal sheet can,
of course, be readily cleaned.

Fourth Type.—The tank, or so- alld batch sys-
tem of heating milk, is quite largely employed.
Heating tanks for this purpose are now manu-

65

THE PASTEURIZATION OF MILK

FROM THE PRACTICAL VIEWPOINT |

factured by many concerns which handle pasteur-
izing apparatus. These batch pasteurizers consist,
as shown in Figs. 12, 13, 14, 14-B, 15, 16, of hori-
zontal tanks, constructed sometimes singly and
sometimes made with two compartments in the same
apparatus. In Fig. 16 we see a tank which is in the
form of an upright cylinder. These tanks are in
some cases surrounded by an insulating jacket.
In others there is an open space between the inner
and outer shell, through which hot water is made

67

THE PASTEURIZATION OF MILK

Fig. 14

FROM THE PRACTICAL VIEWPOINT |

Fig. 14-B

69

THE PASTEURIZATION OF MILK

to circulate, usually by means of a pump. These
tanks have, extending through them in a horizon-
tal direction, some form of agitator. This may be
a tubular coil, as in Figs. 12, 13 and 14-B, or stir-
ring paddles, as in Fig. 15, or it may be coil sus-
pended from above, as in Fig. 16. Some of the
older forms have, instead of a coil of pipe, a series
of hollow screw-shaped discs. In some, as in Fig.
14, there is a tubular structure which is suspended
from the top of the tank and which swings back
and forth by means of a mechanical arrangement.
In operation, these tanks being filled with milk,
hot water is forced through the tubes or discs
above referred to. These coils rotate, keep the
milk mixed and, at the same time, heat it and thus
raise it to the desired temperature. The circulation
of water is maintained in some machines by means
of pumps, the steam for heating being admitted
into the return water shortly before it is again
forced through the coil.

In other machines, as in Fig. 12, the admission
of air into the coil creates a suction which forces
the water through without the use of pumps. In
the form shown in Fig. 15, the heating is accom-
plished in a rather novel manner. In the space

70

FROM THE PRACTICAL VIEWPOINT

Fic. 15

THE PASTEURIZATION OF MILK

between the inner and outer shell, there are placed
near the top two perforated pipes, into which hot
water is forced. The water is thrown through
the perforations, in jets, against the outer surface
of the inner shell. It flows down, following the
contour of the tank, and drops from the bot-
tom, from whence it is again pumped through
the pipes after being reheated. The milk in the
meantime is kept in agitation by means of the
paddles.

In any of these tanks it usually requires from
fifteen minutes to twenty-five minutes to raise the
milk from 50° to a temperature of 145°. The
proper temperature having been attained, the steam
is shut off, and the milk is allowed to remain hot
in the tank for any desired length of time.

The tank form of pasteurizer in practice shows
excellent results. In plants where there are large
quantities of milk to be pasteurized it is necessary
that two, three or more tanks be arranged in se-
ries. This insures a continuous flow of milk
through the cocling apparatus and the filling de-
vices. In actual operation with three tanks, it
occurs that while one tank is being emptied after
heating and holding, the milk is being held in the

72

FROM THE PRACTICAL VIEWPOINT

second tank, while in the third tank the milk is
flowing in and is being heated. These operations
are repeated in rotation.

Many tests have shown that if the water in the
heating coils is heated by injecting steam directly
into the heating coil, the temperature at the inlet
end is rarely above 165°. It may occasionally
reach 175°. Usually it is sufficiently low so that
the milk is not injured by superheating. It can be
readily seen that the temperature at the inlet end
of the coil is much greater than at the outlet end,
since the cold milk takes up the heat, therefore the
heating efficiency of the coil is not equally great
for its entire length. Some attempts have been
made to improve matters by placing a smaller per-
forated coil inside the larger pipe, so that the
water distributed through the coil would have the
same temperature in its entire length.

An objection to the submerged coil is that it be-
comes necessary to have the bearings packed with
some sort of a stuffing-box. Stuffiing-boxes are
always a source of possible danger both on account
of the absorption of milk, which renders cleaning
difficult, and on account of the fact that the con-
stant attrition of the metal at the point of bearing

73

THE PASTEURIZATION OF MILK

creates a condition whereby a metallic taste may
be imparted to the milk.

In the form shown in Fig. 15 the objections
due to uneven heat distribution are at least partly
overcome, since the heat is the same at both ends
and on both sides of the tank.

In Figs. 15 and 16 there are no bearings in the
milk, and stuffing-boxes are therefore eliminated.

It is obvious that when pumps of large capacity
force the water rapidly through the coils, the tem-
perature will be more nearly uniform throughout
the entire length, and a lower initial temperature
can be employed.

_In plants where a comparatively small amount
of milk is to be pasteurized, as frequently occurs
in country shipping stations, one or two tanks will
hold all the milk which is received at a plant each
day. It is therefore possible to use the tank for
several purposes. First, as a dumping tank for
receiving the milk; second, as a heater; third, as
a holding apparatus; fourth, as a cooler, since by
replacing the hot water by ice water or brine in
the coils, the milk can be cooled in the same tank.
Fifth, cans can be filled directly from these tanks.
In using the tank as a cooler, however, it is found

74

FROM THE

PRACTICAL VIEWPOINT

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THE PASTEURIZATION OF MILK

that the time required is usually considerably over
thirty minutes, which is longer than most authori-
ties will allow. In some instances the writer has
found that from an hour to an hour and a half
was required. Where brine can be circulated rap-
idly through the coil, this time can be considerably
reduced, especially if the coil is large. Some spe-
cial tanks are provided with unusually large coils.

In plants which are at a considerable distance
from the point where the milk is consumed, the
tank system of pasteurizing has this added advan-
tage. It is not always possible to get the milk into
the creamery from the patrons and to pasteurize
it before the departure of the milk train. In some
localities the regulations of the authorities specify
that pasteurized milk must be sold within from
twenty-four to thirty-six hours after pasteuriza-
tion. At these distant points it therefore becomes
necessary to hold over some raw milk from day to
day. If a pasteurizing system other than the tank
system is employed, this raw milk is stored in
cans, and a considerable amount of extra labor is
required to handle them. If the tank is used, the
milk which is received on one day may be placed
in the tank and there stored till the following

76

FROM THE PRACTICAL VIEWPOINT |

morning, it being kept cold in the meantime by
the circulation of cold water through the coils.
This milk may be heated on the morning of pas-
teurization as early as necessary to get it ready
for shipment, no handling or transfer of the milk
being previously necessary. ,

In case the tank is used as both a heater and a
cooler, there is of course a considerable strain
upon the joints of the apparatus due to the expan-
sion and contraction of the metal. Those forms of
apparatus are therefore the most desirable which
are the most strongly constructed, and are there-
fore least liable to break. A coil of pipe is
stronger than a screw disc.

Fifth Type—Another process which has been
used to a limited extent for pasteurized milk is
known as bottle pasteurizing. By this method, the
bottles are filled with cold milk and are hermeti-
cally sealed. They are then either placed in a
tank, where they are submerged in water, or else
they are carried under showers of water. In either
case the temperature of the water increases as
the bottles are carried forward. When the de-
sired temperature is reached, the bottles are then
held for the desired time and are then brought

77

THE PASTEURIZATION OF MILK

in contact with cold water, either in tanks or
in showers, till the temperature is sufficiently
reduced.

There is little doubt that from the purely theo-
retical point of view the pasteurization of milk in
the bottle is the ideal method. During the process
not only the bacteria contained in the milk are de-
stroyed, but also whatever bacteria may have been
contained in the bottles and on the caps are also
killed. It can also be seen that the danger of
recontamination after pasteurization is reduced to
the minimum.

There are several forms of apparatus on the
market in which the pasteurization takes place in
the bottle, two of which are shown in Figs. 17 and
18. This method of treatment is very extensively
used in the manufacture of beer. In Fig. 17, the
cases filled with bottles of the milk are carried by
an endless chain conveyor through several tanks
of water in succession. The water in the first tank
is warm, is hotter in the next, and so on till the
maximum is reached, after which the milk is car-
ried into the cooling tanks. The entire process
requires an hour or more.

In the process shown in Fig. 18, an endless plat-

78

FROM THE PRACTICAL VIEWPOINT >

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79

THE PASTEURIZATION OF MILK

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form carries the cases of bottles under showers of
water, of varying temperatures.
When milk is pasteurized by this method, a more
complete cooling is necessary than is the case with
80

FROM THE PRACTICAL VIEWPOINT |

beer. More cooling tanks or additional showers
are therefore required.

In a rather new machine, not shown in this book,
the bottles are placed in a thoroughly insulated box
or compartment, where they are subjected to a
shower of water, the temperature of which is in-
creased or decreased at will by proper regulating
devices on the outside of the apparatus. It is
claimed that with this outfit the heating and cool-
ing is rapidly accomplished, and that the com-
plete insulation of the compartment prevents the
loss of heat. It is also said that, for the same rea-
son, the same apparatus can be used as a cold
storage box, and the treated milk can be allowed
to remain in the apparatus after the completion
of the process till it is ready to be taken out for
delivery. These claims would seem to make it an
especially desirable outfit for small dealers, and
for dairymen in or near the cities where the milk
is to be sold.

The objections which are advanced against
the process of bottle pasteurization are, first, that
the cap which it is necessary to use upon the bot-
tles in order to secure a tight seal is expensive;
too much so to warrant its use upon milk which is

81

THE PASTEURIZATION OF MILK

sold at the popular price. It can, however, be
used on bottles containing milk sold at advanced
prices, like Certified Milk, Grade A, etc. The
second objection is that since the milk expands
upon being heated, the bottles cannot be entirely
filled. ‘The bottles must therefore be made of a
size especially large, and customers must be
taught that bottles which are not full do still in
fact contain the full measure of milk. A third
objection advanced has been that milk in bottles
which are not full is more likely to become shaken
up, and the cream disturbed, than is the case in
bottles completely filled. This objection is
probably not of serious moment. A fourth and
rather serious objection is that the expense in the
consumption of heat units is much greater than
when other methods of pasteurizing are employed.
The reason for this is that the mass of glass in
the bottle nearly equals the mass of the milk, and
that since both bottle and milk must be heated
and also cooled, nearly double the amount of heat
is necessary, and a proportionately great amount
of cooling medium is used. In large plants this
added expense is very considerable.

An attempt has been made to overcome this last

82

FROM THE PRACTICAL VIEWPOINT |

objection, in part at least, by providing a series
of tanks shown in Fig. 19. The five tanks shown
in line No. 1, 2, 3, 4, 5 are used for containing
the cases of filled bottles which are to be heated.
These are lowered into the tanks by suitable de-
vices. The other three tanks behind the pas-
teurizing tanks contain the water to be used in the
process. One, A, contains hot water, which is
kept at a constant temperature by means of a
thermostat. From this tank the water is circu-
lated by means of a pump through the tank, which
at the time contains the bottles which are being
heated and held.

A second tank, C, contains cold water, which is
kept cold either by ice or by a brine coil. This
water is circulated by a pump through the pas-
teurizing tank, in which at the time are contained
the bottles which were being cooled.

The third tank, C, is called a tempering tank.
The water in this is used for regenerative pur-
poses, in the following manner: After a tank full
of bottles has been heated and held for the de-
sired length of time, the hot water is all returned
to the heating tank, rendering the bottle tank
empty of water. Cool water from the tempering

83

THE PASTEURIZATION OF MILK

tank is then admitted. This cools the hot bottles
of milk to a certain extent, and is in turn partly
heated. The water is then returned to the tem-
pering tank, after which the cold water from tank
C is pumped into the tank full of partially cooled
bottles, and when the cooling is complete, the bot-
tles are removed, and the tank is filled with fresh,
unpasteurized bottled milk. The warm water from
the tempering tank, then being admitted, it begins
to warm the cold bottles and is itself cooled.
After its return to the tempering tank it is ready
to be used again in the routine which has been
described, the process being repeated indefinitely.
In this way a large amount of heat is saved which
would be otherwise wasted.

From the illustration and the description the im-
pression is gained that this apparatus would be
rather cumbersome to operate, although it would
no doubt be possible to somewhat simplify the me-
chanical arrangements for shifting the water from
tank to tank. The writer is not personally fa-
miliar with any plant where such an arrangement
is in use.

Another method has been devised for saving
some of the heat otherwise wasted. This consists

84

PRACTICAL VIEWPOINT .

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THE PASTEURIZATION OF MILK

in heating the milk in any good form of pasteuriz-
ing apparatus, and then pouring it, while hot, into’
bottles which have just emerged in a hot condition
from this sterilizing apparatus. The heat which
is usually lost in cooling the hot bottles is in this
way saved. Since, however, the bottles must in
any case be cooled, it can be seen that the cooling,
which usually takes place slowly in the air when
washed bottles are stored in the ordinary way,
must now be accomplished rapidly in order to re-
duce the milk to the proper temperature in the
time required. This necessitates the use of ice
water or brine refrigeration, and since the volume
of glass used equals the volume of the milk, dou-
ble the amount of cooling medium is required than
when only the milk is cooled.

Experiments were made by Ayers and Johnson
in which the heated milk in bottles received a pri-
mary cooling by means of blasts of air at ordinary
temperatures. These experiments indicated that
a considerable economical saving of cooling medium
thus could be effected. Completing the cooling by
means of blasts of chilled air produced satisfac-
tory results. The fact that the cooling process
required a long time seemed to produce no harm-

86

FROM THE PRACTICAL VIEWPOINT |

ful effects upon the milk. There was no noticeable
increase in bacterial content when the cooling was
accomplished within two hours. These results
were obtained under conditions which somewhat
approached what might be termed laboratory sur-
roundings, and it is possible that under the stress
of commercial conditions, difficulties of operation
might develop which would unfavorably influence
the results.

There is one objection which has been raised in
the practice of pasteurization in the bottle which
may have some weight in certain circumstances.
It is claimed that because of the fact that the bot-
tles are tightly sealed, there is no chance for the
escape of disagreeable or offensive odors. In other
heating and cooling processes, a certain amount of
aeration takes place, with, as claimed by some
dealers, beneficial results. Those who advocate
bottle pasteurization claim that during the process
of heating, the objectionable gases are driven out
of the milk and are forced beneath the bottle cap
into the outer air. In so far as known to the
writer, the correctness of this claim has not been
demonstrated. Neither is it known that objec-
tionable odors or flavors have been subjects of

87

THE PASTEURIZATION OF MILK

complaint among the users of milk pasteurized in
the bottle.

An objection which may be a serious one at
times is this. If the bottle caps are not abso-
lutely tight, as may occur when bottle necks are
chipped or uneven, there is an opportunity for
water to be drawn into the bottle. When the cooling
is being carried on there is, of course, a partial
vacuum produced in the space above the milk, and
if in cooling the bottles are immersed in water,
then the water might be drawn into the bottle. If
the water were impure the danger becomes ap-
parent.

A certain advantage in the use of the bottle pas-
teurizing process from a commercial point of view
becomes apparent when only small amounts of
milk are to be treated. If individual dairies are
compelled by legal requirements to pasteurize the
milk sold, it is a comparatively inexpensive mat-
ter to equip for pasteurizing in the bottle. The
only equipment necessary is a tank large enough
to immerse the filled bottles; facilities for supply-
ing hot water to the tank, and also for replacing
the hot water with cold when the heating is ac-
complished. Heat-recording devices are manu-

88

FROM THE PRACTICAL VIEWPOINT |

factured for use in connection with bottle pasteuriz-
ing. When this method is installed in small dairies
there is saved the expense of installing heaters,
holders, coolers, pumps and piping. Equally im-
portant to the dairyman is the fact that the oper-
ating expenses are less, since the amount of ma-
chinery to be kept cleaned and in repair is almost
nothing.

A process of pasteurizing which, so far as known
to the writer, has been but little employed, con-
sists in making use of the vacuum pans which are
commonly employed in the manufacture of con-
densed milk. With certain changes, these can be
used satisfactorily in pasteurizing milk. As usu-
ally constructed, these vacuum pans are retort-
shaped structures made of copper, and contain at
the bottom two or three coils of copper pipe, into
which live steam is admitted. When milk is con-
densed, these hot pipes raise the milk to the de-
sired temperature, and the natural water contained
in the milk is drawn off in the form of steam by
means of the vacuum pipe attached to the top of
the pan. If these pans are used without change
as pasteurizing tanks, it is probable that the live
steam in the heating coils would have a tendency

89

THE PASTEURIZATION OF MILK

to scorch the milk, and it would be necessary to
replace the steam by hot water, which should be
rapidly pumped through the coils, the water being
maintained at a uniform temperature in tanks out-
side the condensing pan. The pans could be used
also for holding the milk after it is heated for any
desired length of time.

In plants where seasonal conditions require that
the milk be used for different purposes at different
times of the year, such an arrangement would
effect a saving of expense ‘in equipment, and
would thus aid in obtaining greater operating effi-
ciency.

From time to time attempts are made to bring
forward some new process for treating milk de-
signed to reduce the number of bacteria in milk
by some agency other than heat. One of these is ©
the treatment of milk by means of an electric cur-
rent. In one electric process, the milk is allowed
to flow from chamber to chamber through orifices
of small diameter. While so flowing it is sub-
jected to a strong alternating current of electricity.
It is claimed that this current destroys the bac-
teria contained in the milk through the shock to
which they are subjected, and that the digestive

90

FROM THE PRACTICAL VIEWPOINT >

qualities of the milk are not impaired, but are
rather improved.

It is, however, found necessary to heat the milk
to about 130° before subjecting it to the electric
current, and during electric treatment it attains a
temperature of about 158°, due to the resistance
of the milk to the electric discharge. It is an
open question whether the destruction of bacterial
life, which undoubtedly takes place, is due to the
electric current or to the heat to which the milk is
subjected. The results of tests made of the milk
so treated indicate that the percentage of bacteria
destroyed is high. If the effectiveness of the appa-
ratus depends upon the heat generated during the
process, it is probable the high percentage of bac-
terial destruction is partially due to the fact that
milk flows in such a small stream through the ma-
chine. Every portion of it is thus uniformly
heated to the maximum temperature, and even
when milk is not held for any appreciable length
of time, it has been found in laboratory tests that
the bacteria are killed. As before stated, it is a
fact that mechanical defects which exist in all ma-
chinery render it difficult to maintain uniform tem-
‘peratures. This makes the holding of hot milk a

91

THE PASTEURIZATION OF MILK

necessary requirement in order to equalize tem-
peratures.

The ultra-violet rays have been suggested as a
means of killing bacteria in milk. Since, however,
these rays have but little penetrating power, it has
been found that the opaque character of milk pre-
vents obtaining the good results which have re-
sulted in the use of the ultra-violet rays in water
purification.

The ozone process, which will by oxidation de-
stroy some forms of bacterial life, and which will
destroy odors, also acts upon the constituent parts
of milk and so changes them that it seems probable
that ozone can never be satisfactorily substituted
for the usual pasteurization process.

An ingenious idea has been brought to the
writer’s attention by which it was proposed to de-
stroy the bacteria by treatment in vacuum. It is
well known that when persons work under abnor-
mally high air pressure as in tunnel construction
under rivers, etc., it is necessary for them to exer-
cise the greatest care in coming out into the normal
air pressure. The air, which under pressure is
absorbed in the bodily tissues, suddenly expands
when the abnormal pressure is relieved. The cells

92

FROM THE PRACTICAL VIEWPOINT

of the body may be strained or broken. In such
case the disease known as “the bends” results. It
has been proposed that a machine might be so con-
structed that an abnormal air pressure upon the
milk could be suddenly released, thus allowing the
air within the germ bodies to quickly expand and
so destroy them. No such system has been made
commercially available.

93

CHAPTER III
HOLDERS

As previously stated, the New York City De-
partment of Health was the pioneer among health
authorities to require that milk, in order to be offi-
cially considered to be pasteurized, must be held,
after heating for a definite length of time. When
this regulation was adopted no holding device was
upon the market which was suitable to be used on
a commercial basis. Since that time most of the
manufacturing firms making milk-handling ma-
chinery have constructed and placed upon the mar-
ket one or more forms of holding apparatus. These
differ in detail, and to a considerable extent in the
efficiency with which they operate. In general,
however, it may be said they are naturally divided
into two classes:

First, those which may be termed absolute
holders, and

Second, those which are of the continuous or
flow type.

Absolute Holders

The absolute holders are so called for the rea-

son that the milk, after being heated, is all held

Q4

FROM THE PRACTICAL VIEWPOINT

in tanks or compartments for a definite length of
time before being discharged.

The first holder placed upon the market was of
this character, and consisted of an upright cylin-
drical tank having partitions radiating from the
centre, thus dividing the tank into eight compart-
ments. Such a holding apparatus is illustrated in
Fig. 20. The drawing, however, shows a later
type of the same apparatus, in which there are
eight separate tanks which are arranged in a cir-
cle. An upright shaft extends through the centre
of the tank or the group of tanks, as the case
may be, to which is attached, at the upper end, a
revolving spout, into which the milk is discharged
through the pipe from the heater. This spout as
it revolves causes each tank to be filled in turn.
To each tank is attached at the bottom an outlet
pipe and valve. These valves are kept closed by
springs, and are opened by means of a revolving
arm, or cam, attached to the lower end of the up-
right shaft before referred to. These outlet pipes
discharge into a common pipe, through which the
milk is conveyed to the cooler. By placing the
revolving inlet spout in proper position with rela-
tion to the revolving cam at the bottom, it can be

95

THE PASTEURIZATION OF MILK

readily seen that each tank will be emptied after
the milk has been held in the tank during the time
required for the shaft to make a complete revolu- —
tion. By properly gearing the mechanism which
operates the shaft it can be seen that the time of
holding can be fixed at will for any period de-
sired. A little thought, however, will make it clear
that the actual holding time will not equal the time
required for the shaft to make a complete revolu-
tion, since approximately one-eighth of this time
is occupied in filling each tank, and one-eighth is
required to discharge each tank. In order to ar-
rive at the actual minimum time for which we can
be sure all the milk is held, we must reduce the
time of revolution by one-fourth, or 25 per cent.
Thus if it is desired to hold the milk for thirty
minutes, it is necessary that the time of revolution
of the operating shaft be forty minutes, which
reduced by 25 per cent. equals thirty minutes, the
actual holding time.

It is also necessary to make sure that the dis-
charge pipes are completely closed before the milk is
allowed to enter through the inlet pipe into any tank.
Otherwise some milk may pass out of the holder
without being held for any definite length of time.

96

FROM THE PRACTICAL VIEWPOINT

97

THE PASTEURIZATION OF MILK

Another point to be observed when partitions
separate the tanks is to make sure that no tank
becomes filled to overflowing. In such case, the -
milk will flow into a tank from which milk is be-
ing discharged, and thus the holding time becomes
a matter of great uncertainty.

In this form of holder considerable foam de-
velops, due to the dropping of the milk for a con-
siderable distance from the discharge pipe into
the body of milk in the tanks. The foamy milk
does not retain the heat as well as is desirable,
and as a consequence the destruction of the bac-
teria is not always sufficiently complete.

In Fig. 21 the eight compartments or wells are
themselves immersed in a tank of water, the tem-
perature of which is kept somewhat above that to
which the milk is heated. In this form of appa-
ratus the tendency to foam is largely overcome
from the arrangement which allows the milk to
enter the well from the bottom. Both the inlet
pipe and the outlet pipe are operated by means of
mechanism, which is above the tanks. ‘There are
sixteen valves, each of which is made tight by a
ground seat, upon which the valve sets. These
valves are at the lower end of the plug shanks,

98

FROM THE PRACTICAL VIEWPOINT |

THE PASTEURIZATION OF MILK

which extend through the milk to the top of the
tanks. Any loosening of these valves, or any in-
accurate adjustment of the eams which operate .
them, may cause milk to be discharged from a tank
before it has been held a proper length of time.
The efficiency of the apparatus would thus be
impaired. .

The fact that the temperature of the heated
milk is not reduced during the holding process
appears to be an advantage. The surrounding
jacket of hot water maintains or increases the
temperature of the milk in the vats.

In Fig. 22 the eight tanks are arranged in a
circle upon a frame or platform, which itself re-
volves, carrying the tanks with it. A central tank,
which is stationary, receives the milk from the
heater. From this tank the milk is distributed to
the various holding tanks by means of pipes,
which radiate from a central valve beneath the re-
ceiving tank. This single central valve is of very
ingenious construction, and is so made that all the
holding tanks are filled and are also discharged
through the same valve. Thus it is seen that this
one valve replaces the sixteen valves which are
employed in such an apparatus as shown in Fig.

100

FROM THE PRACTICAL VIEWPOINT

Fig. 22

101

THE PASTEURIZATION OF MILK

Fig. 22-B

21. The chances of valve difficulties are thus
reduced.

The arrangement of this valve is rather diffi-
cult to describe. It is shown in Fig. 22-B. A
central core is attached to the pipe, which de-
scends into it from the central tank. This core
remains stationary, and is provided with a sin-
gle opening, which is a continuation of and is at
right angles to the discharge pipe from the tank

102

FROM THE PRACTICAL VIEWPOINT |

above it. Outside this core, and closely fitting
it, is a shell which revolves around it. Into this
shell the eight pipes from the various holding
tanks are fastened, and they are so placed that as
the shell revolves each pipe is in turn brought op-
posite to the opening into the inner core. The
milk is thus admitted to the bottom of each hold-
ing tank in turn. As the shell continues to re-
volve each pipe in the outer shell passes in turn the
inner opening and the milk supply is thus shut off
from each particular tank, and so remains until the
shell has nearly completed its revolution. The pipe
opening from the holding tank then comes oppo-
site to another opening in the inner core, which
extends only a short distance into the core. This
opening turns downward and is connected with a
pipe, which discharges the milk to the cooler. Thus
it is seen that each tank is filled in turn and is in
turn discharged automatically. The same method
must be employed for arriving at the minimum
holding time as that used with the device illus-
trated in Fig. 20, namely, the time of revolution
must be reduced by 25 per cent.

The exact holding time may be arrived at in
another way, namely, by carefully noting the

103

THE PASTEURIZATION OF MILK

exact time at which the last milk enters any sin-
gle compartment of the holder, and then observ-
ing the exact time at which the first milk flows
from the same tank. The difference indicates the
minimum holding time. Of course, some of the
milk is held for a longer time than that which is
thus indicated, but we are sure that none is held
for a less time. |

It will be found that the time as observed in
this way is nearly equal to that which we obtain
by calculation, allowances being made for varia-
tions in the mechanical exactness with which the
machine operates.

It will be seen from the illustration that the
various holding tanks are insulated by a cork
jacket, so that little heat is lost during the hold-
ing period. It will be noted, however, that the
pipes leading from the holding tanks to the cen-
tral valve are not insulated, and in this condition
the milk which lies in these pipes during the time
of revolution may, and probably will, become
cooled, and the effectiveness of the bacterial de-
struction will be impaired. This having been
brought to the attention of the manufacturers, they
provided insulating jackets for the pipes as well

104

FROM THE PRACTICAL VIEWPOINT

as for the tanks. Discharge pipes constructed with
these insulating jackets are now provided for ma-
chines which are placed upon the market at the
present time.

A modification of this type of holder is now be-
ing manufactured in which the holding tanks do
not revolve but are made stationary and, instead, the
central valve revolves. The same effect is secured
as in the other type, and there is this advantage,
that less power is required, and the heavy frame
required to hold the revolving tanks is not neces-
sary. There is also this added advantage, namely,
that a small plant may install such an apparatus
with but two or four tanks, and as business ex-
pands there may be added other tanks, it being
only necessary to change the shell of the valve
which revolves about the core.

In Fig. 23 there are seven oblong enamel-lined
tanks which are immersed in a tank of hot water.
These are each filled in turn by means of valves
in a pipe which extends along the upper side of
the series. These valves are opened and closed
by means of an automatic arrangement operated
by a revolving shaft extending parallel to the inlet
pipe. A similar shaft extends along the discharge

105

THE PASTEURIZATION OF MILK

pipe at the bottom of the series, and operates
valves which automatically regulate the discharge
of the milk.

There is one thing which should be carefully ob-
served regarding this form of holder. It will be
noted that the two shafts which operate both the
inlet valves and the outlet valves are impelled by
a single worm-driven gear. Thus both shafts
move in unison. Care must be taken to make sure
that no inlet valve is opened into any tank till the
outlet valve is completely closed, otherwise some
milk will flow out without being held for the
proper length of time.

In calculating the holding time with this appa-
ratus, it must be noted that since there are but
seven tanks in the series, there is required one-
seventh of the entire period of sequence for each
tank to fill and one-seventh for it to be emptied.
Thus the entire time of sequence must be reduced
by two-sevenths. <A little thought will make it
clear that as the number of tanks in a series de-
creases in number, the time of revolution or se-
quence must be increased. With eight tanks a
period of revolution of forty minutes reduced by
25 per cent. would equal thirty minutes. If, how-

106

FROM THE PRACTICAL VIEWPOINT |

\
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3 iB.
Tl
) 9 ed

tu)

nr

Bully

MN it [
Ai ! !
<9

po ae

Fig. 23

107

THE PASTEURIZATION OF MILK

ever, a seven-tank holder has a forty-minute se-
quence, which is reduced by two-sevenths, we have
a holding time of but twenty-eight and four-
sevenths minutes, and so on as the number of
tanks decreases.

A modification of the valve system, shown in
Fig. 23, is now provided by the manufacturers of
this machine. A valve exactly similar in principle
to that shown in Fig. 22-B is made use of. All
tanks fill and empty from the bottom, thus avoid-
ing foam and reduring the danger of by-passing
the milk.

All the types of holders already described are
being used with very satisfactory results. To
summarize the points which should be observed
in either buying or supervising the operation of
holders of this character:

First.—Any serious loss of heat should be pre-
vented by complete insulation of all tanks and
pipes in which the heated milk is held. Of
these insulations, the hot-water jacket is the most
expensive and perhaps the best. There is a
question whether the added expense secures
enough added efficiency to render the expenditure
wise.

108

FROM THE PRACTICAL VIEWPOINT —

Second.—We should be sure that every particle
of milk is held for the minimum time required.

Third.—The valves for admitting and releasing
the milk must be so tightly fitted that no milk
can by any possibility be discharged before the
proper holding time is completed. It may be pos-
sible for valves to become so worn by use that
annular grooves will be worn around them, thus
allowing milk to be by-passed while the valve is
closed.

Fourth—Make proper calculation to determine
that the cycle of filling, holding and emptying of
the tanks is long enough to make sure that the hold-
ing time is sufficient and in addition to allow for
the filling and emptying of the tanks.

Fifth—Make sure that the inlet valve is never
open into a tank before the outlet pipe is closed.

Siath.—Since the ease and convenience of clean-
ing is an item of importance, as a general propo-
sition it may be said that, other things being equal,
a machine which has the fewest pipes and valves
consistent with efficient operation is the most de-
sirable.

Seventh.—It is desirable that as little foam as
possible be produced in the operation of a holder.

109

THE PASTEURIZATION OF MILK

Whatever form of tank holder is used, it is nec-
essary that it be thoroughly sterilized before use
each day, by the admission of live steam for a
considerable period of time. ‘This sterilization is
of importance not alone for the destruction of the
bacteria contained in it, but also in order that the
pipes and tanks may become thoroughly heated im-
mediately before use. If they are not so heated,
it will be found that the milk first admitted to the
apparatus will be considerably cooled, and will be
discharged at a temperature much below that re-
quired by the regulations, and will so continue until
the hot milk has itself slowly heated the appa-
ratus. This may require fifteen or twenty minutes.
It will be found under such circumstances that the
milk first discharged from a holder contains many
more bacteria than that which flows from it after
the machine is heated.

Another form of holder which belongs to the ab-
solute type is that which is represented by the tank
heaters shown in Figs. 11, 12, 13, 14, 14-B, 15, 16,
and previously described. In these the milk, after
having been heated, is allowed to remain for any
desired length of time, and is then released. This
method of holding has produced very satisfactory

110

FROM THE PRACTICAL ‘VIEWPOINT

results. It has this advantage; that the milk
comes in contact with no new metal or apparatus
between the completion of the heating process and
the time when the milk is cooled. One disadvan-
tage is that since it requires considerable time for
a large tank full of milk to be discharged, the last
milk leaving the tank is held for a period consid-
erably longer than that which first flows from it,
and this long holding tends to interfere with the
proper rising of the cream.

Continuous Holders

The continuous or flow type holders differ from
the absolute holders in that the milk, instead of
being quietly held in retainers for a definite length
of time until the required period for holding is
completed, is simply retarded in its flow. This
period of retardation is so extended that before the
milk passes to the cooler it has retained its tem-
perature for the length of time desired.

There are several forms of continuous holders.
One of the first of these is the so-called Park
holder, invented by Dr. William H. Park, of the
New York City Department of Health, and pat-

111

THE PASTEURIZATION OF MILK

FROM PASTEURIZER.

+
°
(@)
©
°
i
rm”
Pp

ented and given to the milk trade for use by the
inventor. It is shown in Fig. 24, and consists
primarily of an upright cylindrical tank, into

112

FROM THE PRACTICAL VIEWPOINT.

which the milk flows at the top, and from which
it is discharged at the bottom. An inverted goose-
neck attached to the outlet pipe so directs the out-
flow that no milk can be discharged until the tank
has become filled. In theory, the hot milk which
enters at the top becomes gradually cooled as it
flows downward, and so the last milk to enter the
tank will be the last milk to leave it. If this
were entirely true, then the time required for fill-
ing a tank would be identical with the holding
time. In such case the various particles of milk
would pass through the tank like a flock of sheep,
one after another. Unfortunately, there are several
disturbing elements which enter into the problem,
and the particles of milk, instead of resembling
sheep, more nearly resemble a flock of chickens
in their behavior. In the first place, the milk
which is nearest to the outside circumference of
the tank becomes cooled more than that which is
in the centre, and as it cools it increases in weight,
and naturally falls to the bottom and goes out.
This tendency is partly overcome by providing in-
sulating jackets. In some cases, as in Fig. 25,
the jacket is a hot-water covering contained in
the space between the inner and the outer shell.

113

THE PASTEURIZATION OF MILK

Again, it can be seen that if the temperature of
the milk as it enters the tank from the heater is
not accurately controlled, it will frequently occur
that the temperature will drop, and this cooler milk
will fall through the body of milk toward the bot-
tom. It is also true that the force of the milk as
it enters the tank from the heater will, unless this
force is broken, tend to carry the milk deeply into
the body of that already in the tank, and so cre-
ate currents which will interfere with the actual
holding time. This force is broken by placing
some sort of a baffle plate under the inlet pipe.
This baffle is sometimes so arranged that it floats
on the surface of the milk, and rises as the tank
becomes filled. In other cases a flat piece of
metal is placed near the top of the tank, and may
or may not contain perforations which allow the
milk to flow through as well as over the edge of
the plate. It is immaterial what form of spreader
is used so long as the currents are broken up. It
will be seen by referring to the illustration that
the inverted U-shaped pipe for the discharge of
the milk is provided with a by-pass valve, so that
the tank can be emptied when the operation is
completed for the day. It is important that this

114

FROM THE PRACTICAL VIEWPOINT.

U-pipe be provided with a vent at the upper end,
otherwise a syphon will be created and the milk
will all be rapidly drained from the tank.

In plants where a large amount of milk is pas-
teurized, and there is therefore a rapid flow, it is
necessary to install more than one of these tanks
in series, and in some instances three and four
tanks are so installed, each succeeding tank being
a little lower than the one before it, and the valves
so arranged that the milk-flow is from one to the
other through the entire series. This also helps
to equalize any uneven temperature which may oc-
cur as the milk is discharged into the first tank.

With all these precautions to insure a steady
and even flow, it is never safe to assume that the
holding time is correct unless a test is made. Only
two feasable means of so testing the tanks have
developed. One is the color test and the other
the temperature test. Neither are absolutely ac-
curate, but are sufficiently so for practical pur-
poses.

In the color test, the tanks are filled with water,
heated to the same temperature as is the case when
milk is pasteurized. The time of filling having
been observed, a solution of some intense color,

115

THE PASTEURIZATION OF MILK

preferably methylene blue or uranin, is allowed
to flow into the tank with the heated water. The
time is observed between the time of its introduc-
tion and the time when the first trace of it appears
at the outlet. In order to make the test as ac-
curate as possible, care should be taken that a com-
plete solution is made of the color, otherwise small
particles of solid color may fall through the liquid
and deceive the observer. The solution of any
color is of course slightly heavier than the liquid
in which it is dissolved, and the tendency is for
it to fall after its introduction. Therefore, the
solution should be made as nearly as possible of
the same specific gravity as the water in the tank.
If it can be made slightly less in weight than the
water the result of the test will be rather better.
Even with the greatest care, it seldom happens that
two tests of the same apparatus will bring iden-
tical results. Unless the speed of flow is accu-
rately gauged, the results will differ.

The temperature test is sometimes used to de-
termine the efficiency of these holders. When this
method of testing is employed it is the practice to
fill the holders with water in the same manner as
with the color test. The temperature of the water

116

FROM THE PRACTICAL VIEWPOINT |

as it leaves the heater is then suddenly raised
5° to 10°, and the time at which the rise takes
place is noted. A careful watch is then kept at the
outlet of the holder to determine when any rise in
temperature occurs at this point. The elapsed time
indicates the time of holding. The temperature,
instead of being raised, may be lowered a given
amount at the heater, and the corresponding drop
in temperature at the outlet noted.

The inaccuracy of this method of testing is due
to the fact that during the long holding period
there is a natural tendency for the changed tem-
perature to become diffused throughout the sur-
rounding liquid. It can also be seen that when
the temperature is raised the natural tendency is
for the hotter liquid to remain on top of the tank,
while if the temperature is dropped, the tendency
is for the cooler liquid to settle toward the bot-
tom of the tank. A graphic chart can be made
showing the result of these tests very clearly.
Using the upright gradations of the chart to indi-
cate changes in temperature, and the horizontal
gradations to indicate periods of time, the sudden
rise at the heater will be clearly shown by an al-
most perpendicular line. The line showing the

117

THE PASTEURIZATION OF MILK

rise of temperture at the outlet will be compara-
tively gradual in its rise and will not reach its
highest point for a considerable time. It will also
be found that the proportional rise in temperature
at the outlet will not be as great as at the inlet
of the holder. When the temperature of the inlet
is dropped instead of being raised, it will be found
that the change of temperature at the outlet occurs
in a much shorter space of time.

In choosing between the color test and the tem-
perature test, it can safely be said that for the
Park holder the color test is the more accurate.
When the tubular holder is used, which will be de-
scribed later, it is probable that the two tests are
nearly equal in accuracy.

When two or more tanks are employed in series,
it is desirable that the piping be so arranged that
the lowest tank can be filled with milk first when
the process of pasteurizing is commenced for the
day, and then when the lower tank is full the up-
per tanks should be filled and the process contin-
ued in this manner. The milk will then flow
through all the tanks in succession from the high-
est to the lowest. The reason for filling the lower
tank first is as follows: When each tank is first

118

FROM THE PRACTICAL VIEWPOINT

filled, the milk of course falls from the inlet pipe
at the top to the bottom of the tank, and afterward
onto the surface of the body of milk in the tank as
it fills up to the level of the outlet pipe. In conse-
quence there is considerable agitation of the liquid
and currents are created. This may cause the last
milk which enters the tank to be the first to be
discharged, and our holding time becomes a mat-
ter of uncertainty. If, however, the lower tank is
the first one filled, we are then sure that all the
milk in this tank is held for at least the time re-
quired for the other tanks to fill.

This method of filling may be effected in either
of two ways: First, a pipe may extend along the
top of the tanks in such a way that by opening the
proper valves the milk may be directed into either
tank at will. Second, the pipe may be arranged
at the bottom of the series in such a way that
either tank may be filled, if the proper valves are
opened and closed. Both arrangements of pipes
are shown in Fig. 24.

It has been found by tests that this form of
holder never holds the milk for a period of time
as long as that which is required for them to be
filled. Depending upon the form of the tanks and

119

THE PASTEURIZATION OF MILK

the method of construction, the percentage of hold-
ing time to filling time is from 25 per cent. to 70
per cent. It is usual to estimate the time as 60 per
cent. of the filling time. It is true that tanks which
are tall and of comparatively narrow diameter are
more efficient than are short and wide tanks, the
reason probably being that with long, narrow tanks
the movement of milk is comparatively rapid, and
there is less diffusion of the milk than when the
movement is slow, as in the wide, short tank. Tests
have been made which indicate that when the rate
of flow is twelve feet or over a minute, there is
very little diffusion of the liquid.

In all tanks of this character it is desirable, and
indeed almost a necessity, that some sort of an
insulating jacket be provided in order that there
be as little loss of temperature as possible during
the holding process. The reason for this, as be-
fore stated, is that the cooling of the milk which
is near the outer circumference of the tank causes
downward currents. Thus the milk which falls
to the bottom on account of these currents is car-
ried out of the tank before it has been held for the
proper length of time.

The insulation may be provided by means of

120

FROM THE PRACTICAL VIEWPOINT

jackets of asbestos, cork or felt, or a surround-
ing tank of water may be provided, as in Fig. 25.
By means of the insulation, if properly applied,
the heat will be retained and the milk as it flows
from the tank will have a temperature but little
below that at which it enters. When the hot water
insulation is used, as in Fig. 25, the initial tem-
perature of the milk may become somewhat in-
creased during the holding period. This addi-
tional heating, it can be seen, has a tendency
to cause the milk which may enter the tank below
the average temperature to become heated and rise
toward the top of the tank, thus increasing the
time for which it is held. As a matter of fact, the
water-insulated tanks have shown a good percent-
age of holding time as compared with the filling
time when the color test has been applied. The
test of their efficiency as measured by the destruc-
tion of the bacteria contained in the milk is also
good.

This Park type of holding tank has been some-
what modified by various manufacturers in this re-
spect, namely, by introducing the milk at the bot-
tom and allowing it to flow out at the top instead
by the reverse method of flow. When the inlet

121

THE PASTEURIZATION OF MILK

pipe from the heater enters the tank at the centre
of the bottom, and the milk is forced upward till
the tank is filled, the color tests made have indi-
cated that their efficiency percentage was small.
Especially was this true when the outlet pipe was
at one side and near the top of the tank. It can
be seen that the force which is necessary to impel
the milk in at the bottom against the weight of
the superimposed milk in the tanks must of neces-
sity create currents. This will be more noticeable
if the milk is forced through the heater by means
of a pump. The impulses will create a somewhat
uneven flow and the resulting currents will be
greater. The discharge of the milk from one side
of the top also tends to cause currents and an
uneven overflow.

One manufacturer has so constructed his tanks
that the inlet pipe enters at the top through the
cover, is carried down through the body of the
milk in the tank to the bottom, and then dis-
charges the milk into the tank by means of an
enlarged perforated foot somewhat resembling a
sprinkler head on a watering can. In the plants
where this apparatus is used the milk flows by grav-
ity and there are thus no pump impulses. The

122

FROM THE PRACTICAL VIEWPOINT |

force is broken up by the descent of the milk
through the body of that in the tank. It can be
seen that when the milk as it enters the tank is be-
low the average temperature, the tendency will be

123

THE PASTEURIZATION OF MILK

for it to remain at the bottom, and so be heated
before it is discharged. In this holder, also, the
outflow is from the top, but the flowage into the
discharge pipe is from many points at the surface
into a gathering pan. In this way surface cur-
rents are avoided.

One of the disadvantages of the upright tank
holder is that when it is of large size it is rather
difficult to clean. It becomes necessary for the
workmen to get inside the tank in order to thor-
oughly clean it. Some upright tanks are being
made which are mounted upon trunions in such a
way that when the pipes are disconnected the tank
may be turned into a horizontal position, and the
cleaning can then be more easily performed.

A second form of continuous or flow type tank
is so constructed that a long horizontal tank, which
opens at the top, is divided by cross partitions into
several compartments. At the top of each of these
partitions is a gathering trough, extending along
the upper edge of the partition. A tube attached
to the centre of this trough extends to near the
bottom of the next succeeding compartment. This
is shown in Fig. 26.

In operation, the milk enters into the compart-

124

FROM THE PRACTICAL VIEWPOINT

Fic. 26

ment at one end of the tank, and when the com-
partment is full, the milk flows into the gathering
trough and is carried by means of the tube to the
bottom of the succeeding compartment. Here the
same routine is repeated till all the compartments
are full. Then the flow becomes continuous till
all the milk is pasteurized. When all the milk has
left the heater, of course the flow from the holder
stops. The tanks are at this time all full, and
it is then necessary to remove the plug which is

125..

THE PASTEURIZATION OF MILK

near the bottom of each compartment in turn
till all are emptied. Since these plugs are re-
moved by hand, it is necessary to place the hand
and arm into the empty compartment at each
operation. The danger of contamination is thus
evident.

When the partitions are low it has been found
that the milk flows over the tops of all of them,
and there is thus but little holding time possible,
since the milk flows almost directly from the inlet
to the outlet pipe. Even with the best of con-
struction, tests have shown that the percentage of
holding time to the filling time is small, sometimes
being as low as 10 per cent. to 15 per cent.

The third form of continuous flow type holder
now used quite extensively is shown in Fig. 27. It
consists of a series of large-size tubes arranged in
a box-like structure. These tubes are connected
one with another at the ends by suitable hinged
heads, so that the milk which enters the top tube
of the series flows forward and backward through
all of them and is discharged from the lower tube.
The discharge pipe is carried upward in the form
of an inverted U tube in a similar manner to that
shown in Fig. 24. This gives assurance that no

126

FROM THE PRACTICAL VIEWPOINT:

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127

THE PASTEURIZATION OF MILK

milk will be discharged until all the tubes have
become filled.

In this form of holder, the flow of milk through
the apparatus is comparatively rapid. As before
stated, this rapid flow tends to prevent diffusion,
and the holding time more nearly approaches the
time required to fill the apparatus than in any
other form of flow-type holder. In some respects
it is rather difficult to make a satisfactory color
test upon this holder on account of the fact that
the air, which of course fills the holder when the
filling with milk is commenced, is not all forced
out as completely as is desired, and thus air pock-
ets are formed. It thus occurs that some milk is
forced from the discharge tube before the appara-
tus is completely filled. Thus it is difficult to ob-
tain the exact time required to fill the tubes. It
is claimed by the manufacturers that when it is
operating under the most favorable conditions the
milk will be held for 98 per cent. of the time re-
quired for the apparatus to become filled. The
tests observed by the writer indicate that the hold-
ing time is from 80 per cent. to 90 per cent. of the
filling time, which is a greater percentage than
with other holders.

128

FROM THE PRACTICAL VIEWPOINT

The same difficulty which is experienced in
emptying the tubular heater is observed with rela-
tion to the tubular holder. This is due to the very
slight inclination or pitch of the tubes from the
horizontal. In some cases it has been the prac-
tice to force the last milk out of the tubes by fol-
lowing it with water. The possibility of adul-
terating the milk unless great care is exercised is
apparent. In the later machines made, the tubes
are given a greater pitch, and the objection due to
slow drainage is at least reduced.

It should be noted that unless the tubes are very
thoroughly heated by means of hot water or steam
immediately before use, the first milk entering the
holder will be so cooled that its temperature at the
discharge will be below that which is required.

This form of holder can be easily cleaned, since
the tubes are large, and can be readily opened.
It is thus easy to force a suitable brush through
the pipes, and it is not difficult to see if all dirt
has been removed. It is of course necessary that
the cleaning be performed with great thorough-
ness in order that it be effective in the destruction
of bacteria.

Whatever form of holder is used, whether it be

129

THE PASTEURIZATION OF MILK

of the absolute or the continuous type, careful
sterilization should be practised, not only directly
after the apparatus is washed each day, but also
immediately before its use on the following day.
The reason for this is due to the fact that any
organic matter which may remain in the apparatus
after washing may contain spores of bacteria
which are not readily killed by the heating to
which the apparatus is usually subjected. These
spores may develop into active bacteria during the
time that the apparatus remains idle. Especially
would this be true if, as usually occurs, consid-
erable moisture is allowed to remain in the machine.
For this reason the holder should be thoroughly
sterilized before use each day. It may here be
noted that there is even a greater necessity for
sterilizing the cooler, pipes, bottling machine, etc.,
with which the pasteurized milk comes in contact
after leaving the holder. Any recontamination at
these points is not afterward corrected and may
be a source of danger.

It should here be noted that a feature which
has been introduced into some milk plants con-
sists in a brief superheating of the milk after it
leaves the holder. This is accomplished by allow-

130

FROM THE PRACTICAL VIEWPOINT

ing the milk to flow in a thin layer over pipes
which are heated to about 162° to 165°. The milk
is then immediately cooled. It is claimed that bac-
teria which are resistant to 142° temperature are
nevertheless considerably weakened by this heat-
ing, and are completely destroyed at the brief
heating of 162°. It is also claimed that the cream
rises in a more satisfactory manner when the ad-
ditional heating is employed. The feature of ap-
plying a brief superheating temperature to milk
already pasteurized has been covered by a patent.
It must be evident, when a little thought is
given to the matter, that in order for any con-
tinuous holder to be reliable, the rate of milk flow
must be uniform. In very few forms of appara-
tus is there any attempt to properly control the
rate of flow. When milk flows by gravity, the
rate at which it flows into the heater will depend
partly upon the volume of the fluid in the tank
which feeds the machine. When a pump is used
to supply the heater, its rate of delivery may be
influenced by the steam pressure, or by the degree
to which the steam valve is opened, or by the con-
dition of the valves and pistons. In places where
a gravity flow is employed, it is not a difficult mat-

131

THE PASTEURIZATION OF MILK

ter to arrange a feed cup which will make it cer-
tain that no more than a definite amount of milk
can reach the heater per hour. When a pump is
used, a float valve in the tank which feeds the
heater can be made to shut off the intake pipe to
the feed tank. This increases the milk pressure
upon the pump and the discharge pipe, and by
means of a suitable valve this increased pressure
is made to close the steam valve which supplies the
pump. This method of controlling the flow of
milk to the heater is in successful operation in
several pasteurizing plants.

132

CHAPTER IV
TEMPERATURE CONTROLLERS AND RECORDERS

In order that uniformly good results in the pas-
teurization of milk may be obtained, it is abso-
lutely necessary that the temperature to which the
milk is heated be controlled in such a way that
there will be no great variation. In order to con-
trol this properly, three things are necessary—
first, a uniform, even flow of milk; second, a steam
pressure which does not vary; and third, that the
steam which is admitted to the heater be so con-
trolled that whatever variations there may be in
the temperature of the inflowing cold milk may be
met by varying amounts of steam, admitted to the
heater. This control will, of course, also prevent
any excessive heating which would follow if too
much steam entered the heating apparatus.

The matter of an even milk flow has been dis-
cussed in the previous chapter.

The control of steam pressure may be accom-
plished in various ways. It is, of course, necessary
that there be sufficient boiler capacity to insure
that the steam pressure does not fall below a cer-

133

THE PASTEURIZATION OF MILK

tain minimum amount. One of the simplest meth-
ods of steam pressure contro] is by an instrument
constructed like the safety valve of a boiler. A
movable weight upon an arm regulates the pressure
which is desired. When properly set any increase
of pressure above the desired amount lifts the arm
and shuts the steam valve connecting with the pipe
leading to the heater. Other more complicated
forms of apparatus are on the market, the details
of which it is not necessary to describe.

In the matter of the control of the temperature
at which the milk leaves the heater, it is, of course,
possible to do this by hand. This method makes it
necessary that a man constantly watch the ther-
mometer attached to the outlet milk pipe, and at
the same time open or close the steam valve to ad-
just the steam flow to the varying temperature of
the milk.

If the speed of milk flow, and also the steam
pressure is well controlled, it is possible for a care-
ful workman to regulate the milk temperature with
good success. If, however, these factors are con-
stantly varying, it is nearly impossible for even a
careful man to obtain good results. It is, of course,
more economically efficient to arrange for auto-

134

FROM. THE PRACTICAL VIEWPOINT

matic temperature control than to depend upon
man power, provided, of course, that the machine
works as it is intended to work.

The machines designed to control temperatures
are operated in two ways. In one machine the
bulb which is inserted into the milk is filled with
some volatile liquid like ether and is connected
by means of a capillary tube with a pressure coil,
which in turn regulates the flow of compressed air
to a valve. The compressed air is employed as a
motive power to operate the valve which regulates
the admission of steam to the milk heater. Such a
system involves the installation of an air pump
and a tank for the storage of compressed air. To
one unfamiliar with the apparatus the description
may appear involved and the operation compli-
cated. Fig. 28 shows this system.

In another form of controller, electricity is em-
ployed as a motive power in operating the steam
valve instead of compressed air. The bulb which
enters the milk contains two metals, which are so
fastened together that the difference in expan-
sion makes and breaks the electrical connection
and the steam valve is operated by this means.
This is shown in Fig. 29. This method can, of

135

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THE PASTEURIZATION

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course, be employed only where an electric current
is available. This current, however, may be fur-
nished by a small inexpensive dynamo, which can
be operated at any plant where power is available.
Both these forms of control work in a satisfactory
manner. Of course, they are somewhat delicate

137

THE PASTEURIZATION OF MILK

in adjustment, and careful handling is necessary.
Kither form will control the milk temperature
within 2°, as indicated by the temperature re-
corder.

A method of temperature control which was
proposed by the writer some years ago had for its
basis a principle which has been made use of
in this connection to a limited extent only. This
consisted in this, namely, that the temperature of
the heating medium be so controlled as to remain
constant, and that the milk which flowed out of
the heater be kept at a uniform temperature by
varying the speed of flow of the milk through
the heater. This reverses or inverts the present
practice, in which the speed of milk flow is con-
stant, while the temperature of the heating med-
ium varies. The proposed method would have
this advantage, that no part of the milk could ever
be heated higher than the temperature of the water,
and if this water temperature were controlled by
a thermostat no scorching of the milk would ever
result. It is evident that with a uniform heating
medium the milk which flows through the heater
will take up more of this heat if the speed of flow
is slow than it will if the milk moves rapidly over

138

FROM THE PRACTICAL VIEWPOINT

the heating surface. A thermostat attached to the
milk outlet pipe from the heater could be made
to control the steam which supplied the milk
pump. This would vary the speed of milk flow.
If milk flows by gravity to the heater, the ther-
mostat might be made to open or close a valve in
the feed pipe.

The nearest approach to the use of this prin-
ciple occurs in some plants when the heated water
is kept at a uniform temperature by a thermostat,
and the milk flow is also constant. The heating
surface of the heater is so very large compared to
the amount of milk heated, that the water is never
more than 3° or 4° hotter than the milk, and
there is therefore no possibility of scorching the
milk. In these plants also the efficiency of the re-
generative principle is carried as near the theo-
retical limit of perfection as it seems possible. The
water leaving the heater is within a few degrees of
the temperature of the cold milk entering the ma-
chine. This cooled water is conveyed to the milk
cooler, where it is used for cooling the hot milk.
It becomes so heated when leaving the cooler that
it is but a few degrees lower than the hot milk.
It can be seen that but little steam is required to

139

THE PASTEURIZATION OF MILK

again raise the temperature to the desired point.
The increased amount of heating and cooling sur-
faces required for this form of pasteurizing ma-
chine calls for careful cleaning and sterilization.

Automatic Recorders

The automatic recording of the milk temperature
is desirable, and in most cities where the pas-
teurization of milk is subject to public control it
is required. The milk company which is really
anxious to put out a safe product wants an office
record which will indicate whether the work is
being properly performed. With health authori-
ties, such a record is necessary, since it is impos-
sible for inspectors to be at pasteurizing plants all
of the time to watch their operations. A correct
automatically made record is the best substitute
for personal inspection. To be of ideal value, such
a record should show, not only the temperature, but
also the time of holding. When the tank or batch
heater is used, the single recorder attached to the
tank will show these items with fair accuracy, but
the observer must note whether or not the cooling
is either wholly or partially done in the tank itself.

140

FROM THE PRACTICAL VIEWPOINT

If such cooling in the tank does take place, then
the length of time for which the recording mark
remains at the highest point is a correct indica-
tion of the time for which the hot milk is held.
If the cooling is performed entirely outside the
holding tank, then allowance must be made for the
time necessary for the milk as drawn from the
tank to fall below the point where the thermome-
ter bulb is inserted into the milk. It is plain that
the making of the record by the recorder pen will
continue as long as the bulb remains in the hot
milk. Thus, if the highest temperature were re-
corded for forty-five minutes, and it required twen-
ty-five minutes for the milk in its discharge to fall
below the recorder bulb, then the actual holding
time for all of the milk would be but twenty
minutes.

When the continuous holding process is used, it
is desirable that a recorder be attached to the out-
let of the heater, and that another be placed in the
outlet pipe from the holder. If the charts on these
two recorders are both set at the correct hour of
the day then it is easy to calculate the duration
between the time of the first discharge of hot milk
from the heater and the first discharge from the

141

THE PASTEURIZATION OF MILK

holder. If one recorder only is in use, it is more
important that it be placed at the holder outlet.
It is evident that if there is a serious loss of heat
during the holding process due either to imper-
fect insulation or to insufficient preliminary heating
of the holder, then the milk would not be satisfac-
torily pasteurized, since some of the dangerous
organisms originally in the milk may escape de-
struction. The holder recorder indicates this.

The various recording instruments upon the
market differ in this one particular, namely, that
in one form ether, or a similar volatile fluid, is
used in the thermometer bulb and capillary tube,
while in the other, the bulb and tube are filled with
mercury. One of the former is shown in Fig. 30,
while the mercury bulb is shown in Fig. 31. There
is a variation also in the method employed for
regulating the recording arm. In a form of re-
corder not shown, another form of adjusting screw
is attached to the recording arm, and an improved
device is used for securing the paper chart to the
face of the instrument.

In the selection of a recording instrument, one
of the most important points to consider is its sen-
sitiveness to rapid or frequent changes in tempera-

142

FROM THE PRACTICAL VIEWPOINT

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ture. If it is slow in responding to such changes,
there is a possibility that there may be a wide
fluctuation of temperature, which will not be shown
upon the recording chart. The manufacturer of
each instrument claims that his machine is very
sensitive to rapid temperature changes.

It should be borne in mind that a temperature

144

FROM THE PRACTICAL VIEWPOINT |

recorder is in reality a pressure recorder only in
which the changes in pressure due to varying tem-
peratures are so graduated as to indicate with
fair accuracy the temperature of the milk. With
the ether instrument, the amount of movement of
the arm for, say, a ten degree rise, changes as the
higher temperatures are reached. So the grad-
uations on the chart are not of the same width all
the way across. In the mercury instruments this
is not true, but the degree graduation lines are
equally distant one from the other. There are cer-
tain inaccuracies in these instruments which must
be taken into account. Thus it can be seen that
the temperature of the room in which the recorder
is placed must have an effect upon the pressure
coil. In the instrument shown in Fig. 30 an at-
tempt is made to correct this by attaching to the
arm a compensating coil. This coil also contains
mercury, and is so placed that it moves in a di-
rection opposite to that of the coil to which the
capillary tube is connected. The recording arm
is attached to both coils. When, therefore, both
coils move as the result of the room temperature,
no effect is produced upon the recording arm, but
it remains stationary. Any increased pressure in

145

THE PASTEURIZATION OF MILK

one due to the temperature of the heated milk will
move the pen and cause it to make a proper rec-
ord. The same effect may be produced in another
way. In this case the compensating coil is con-
structed of two different metals, and the differences
in expansion cause it to move, but in a direction
opposite to that produced by the ether coil.

It must also be borne in mind that the recorder
does not register absolute temperatures, but only
relative changes in temperature. Thus inaccurate
adjustment of the arm may produce a record which
is deceptive. For this reason it is necessary to
provide some means of adjusting the arm in order
to secure an accurate reading. In some instru-
ments the arm has a flexible joint which can be
moved by hand. This is rather difficult to accom-
plish, without danger of breaking the recording
arm, and fine adjustment is not easy. There is
also the danger that the joint will be uninten-
tionally moved when placing the chart upon the
face of the dial.

In one recorder a post is so placed that it can
be turned by means of a clock key. After the
proper adjustment has been made, the post may be
held in proper position by sealing it to other rigid

146

FROM THE PRACTICAL VIEWPOINT

posts beside it. This form is of value to the in-
spector, since by placing his seal upon it he can
be sure that no change is made in the recorder
during his absence.

In other instruments other means of adjustment
are provided. If, as in some forms, the coil is so
placed that its axis of rotation is the same as that
of the recording arm, then no movement of the arm
at the joint can affect the relative temperature
valves of the varying degree spaces upon the chart.
With this form there appears also to be less lia-
bility to vibrate with the vibration of the walls of
the buiding in which it is placed. This form also
has the advantage that the knob or screw which
holds the chart to the face of the dial is so ar-
ranged that the chart cannot be left loose upon the
apparatus, but must either be securely fastened
or left off the instrument altogether. It is also
very easy to fasten the chart to the clock face.

It has frequently been found by inspectors that
instruments were not accurately adjusted. This
may be due to a defect in the instrument itself, or
it may be due to an intentional false adjustment
by the man who is operating the pasteurizer. He
may wish to indicate upon the chart a higher tem-

147

THE PASTEURIZATION OF MILK

perature than is actually employed in the pas-
teurization of the milk. For this reason those in-
struments whose adjustment is under the control
of the inspector alone are desirable. They should
be frequently tested. This frequent checking is of
advantage to the honest milk dealer as well, since
if a recorder by any means shows a temperature
lower than it should, there may be trouble with
the cream line due to an unsuspected high tem-
perature in the pasteurizer.

Health authorities must be alert in watching the
temperature records which are kept on file by the
dealer. It is, of course, possible for a dishonest
dealer to make false records. These may be made
in various ways. Instances have been known
where the entire record has been made by hand,
an ordinary pen being used. This requires more
skill than the average dealer possesses, if he is to
deceive the wideawake inspector. It is possible
to put a chart upon a recorder dial and leave it so
loosely attached that it does not revolve with the
clock. Then, when the desired temperature is
reached, the chart may be turned by hand and a
beautiful even line be drawn upon it. When the
first milk from a holder has a temperature lower

148

FROM THE PRACTICAL VIEWPOINT |

than required by law, some dealers wait until the
proper temperature is attained, and then, by plac-
ing the thermometer bulb in the milk, they get a
record which indicates an immediate rise of tem-
perature to the highest point, and then a uniformly
even line. Any record which indicates that the
temperature has been raised at once to the maxi-
mum point, and then continues with no variation
during the entire run, should be looked upon with
suspicion. Inspectors with a little experience soon
learn to detect false records, by evidences not al-
ways easy to explain, and they are able to gain
from dealers the admission of irregularities which
are at first denied.

149

CHAPTER V

CLEANING AND COOLING THE MILK—CLEANING
CONTAINERS——-HOME PASTEURIZATION, ETC.

It is of course needless to say that all milk
should be clean when it arrives at the plant where
it is to be pasteurized. That is, there should be no
visible dirt in the milk. It is also desirable that
all dirt which is not readily detected be absent.
While visible dirt and bacteria are not identical,
still it is true that visible dirt is almost always ac-
companied by bacteria in large numbers. Dealers
should therefore make every effort to induce the
dairymen to be so cleanly in their methods that
very little dirt will find entrance into the milk.
The sediment test when properly used is an ex-
cellent method of finding out whether or not the
dairyman is cleanly in his methods. If, however,
the producer is allowed to strain his milk before
bringing it to the shipping station, then the sedi-
ment test simply tells the dealer whether or not
the farmer has strained the dirt out. Or rather,
let us say it indicates either that the farmers’
methods of caring for the milk are cleanly, or that

150

FROM THE PRACTICAL VIEWPOINT

the evidence of his uncleanliness has been strained
out. It seems wise to advise dealers to prohibit
the straining of milk at the farm. This may
seem like radical doctrine, but a little thought dis-
closes its wisdom. If the milk is unstrained, then
the sediment test becomes of real value to the
dealer in directing his attention to those dairymen
who need attention from the inspector. Then,
again, after the dirt once gains access to the milk,
the straining simply removes that part of the dirt
which is the least objectionable, namely, the in-
soluable part. If milk is poured over a strainer,
the dirt remains upon the surface, and the milk
which may be afterward poured through the
strainer helps to carry through those soluble por-
tions which may have at first escaped solution.
This soluble portion, of course, contains most of
the bacteria.

The removal of the dirt at the shipping sta-
tion or the pasteurizing plant may be accom-
plished by straining as it is received, or since the
straining of cold milk is difficult, it may be strained
while hot from the heater and before it enters the
holding apparatus. There is no objection to this,
since whatever bacteria are carried through into

151

THE PASTEURIZATION OF MILK

the holder are destroyed during the holding
process.

Clarification

The centrifugal clarifier is used to a large ex-
tent, and removes not only the dirt which is ordi-
narily seen in milk, but also the pus cells, blood
cells, etc., which usually escape detection. The
clarifier, as is well known, is made in a manner
similar to a separator, the difference being that
the cream is not separated from the milk, but the
dirt, pus, etc., is thrown against the outer por-
tions of the revolving shell, and is there collected.
Of course, this material contains a great many bac-
teria, which are carried along with the heavier ma-
terial. Tests, however, made by the plating
method, do not show the great decrease in the
number of bacteria which might be expected, and —
in many instances the apparent number is in-
creased. This is probably due to the fact that the
clumps of bacteria are broken up and so produce
more colonies upon the plate than results when
they remain bunched together in the original milk.
One of the clarifiers is illustrated in Fig. 32.

One objection to the clarifier has been the

152

FROM THE PRACTICAL VIEWPOINT

THE PASTEURIZATION OF MILK

tendency which there was to create foam, espe-
cially if the milk were cold. This foaming is due,
of course, to the entrance of air into the milk dur-
ing the process. Milk which has been previously
pumped seems more likely to foam than when
pumps have not been used. Machines are now
made by which the air is excluded, and no foam,
or almost none, is produced when they are oper-
ated, even when the milk is cold. It is generally
held that the clarification of milk by a centrifugal
machine is a good thing. It is claimed that the
pus cells, leucocytes, etc., which are in the milk,
tend to form a covering for the bacteria contained
in the milk, to such an extent that they are some-
what protected and are not so readily destroyed
by heat. It is claimed that the removal of this
covering by means of the clarifier therefore assists
in the complete destruction of the bacteria. This
claim has not been fully demonstrated to the knowl-
edge of the writer.

It is the practice of some dealers to strain the
pasteuried milk as it enters the bottling machine.
This is to be condemned unless the strainer is
completely covered and is sterilized at the same
time that the final sterilizing of the bottler occurs.

154

FROM THE PRACTICAL VIEWPOINT |

In fact, any straining after the milk leaves the
holding apparatus is undesirable, and seems to be
useless if the milk has been well cleaned before
pasteurizing.

Coolers

The rapid cooling of heated milk has been held
to be an important factor in the satisfactory pas-
teurizing of milk. It was claimed that the sud-
den chilling had a destructive effect upon the bac-
teria, which had been already weakened by the
heating. Investigations made by Ayers and John-
son, however, seem to indicate that when the cool-
ing is accomplished, during a period of two hours,
there is no noticeable increase in bacterial growth.

There are three general types of milk coolers
in use:

First: The open cooler or aerator. This consists
of a series of tubes, made usually of copper and
well tinned. These tubes are arranged one above
another, and are so connected at the ends that cold
water or brine is forced through the entire series.
The water flow is into the lower tubes and up-
ward through the series, so that the coldest water
comes in contact with the coldest milk. This form

155

THE PASTEURIZATION OF MILK

Fic. 33

of cooler is shown in Fig. 33. The cooler is usu-
ally arranged in sections. Through the upper
section cold water, frequently well water, flows,
while the lower section contains ice water or brine.
This form of cooler is very effective in rapidly

156

FROM THE PRACTICAL VIEWPOINT |

cooling the milk when it is made large enough to
take care of the milk which is to be treated. They
are made by various manufacturers in forms which
vary somewhat in details. Some are so arranged that
the regenerative principle is made use of. In most
of these the hot milk from the holder is allowed
to flow over pipes through which the incoming
cold milk flows. This is a means of saving heat
units, but such coolers are rather difficult to clean,
and there is a danger that the pressure of the cold
milk on the inside of the pipes will find openings
through which the milk will be forced into the pas-
teurized milk on the outside. The contamination
which results is not corrected by repasteurization.
Some one may say that the same danger exists when
the cooling medium on the inside of the pipes is
water. This is true, but it must be remembered
that the water pipes do not need to be taken apart
for cleaning, while the milk pipes must of neces-
sity be opened for cleaning daily, and the danger
from loosened joints is therefore greater.

Another objection which has been urged to the
use of the open cooler is that the milk is exposed
to the air, and that there is great danger from
air contamination. This is true when the air is

157

THE PASTEURIZATION OF MILK

full of dust or foul odors. In most milk plants,
however, the air is so moist that little dust is flying
about, and recent investigations by Ruehle and
Kulp * of milk contamination by stable air indi-
cate that even under unfavorable conditions the air
contamination is not as serious a matter as we have
supposed. Of course, milk coolers can be en-
closed by tightly fitting metal covers, or they may
be located in separate rooms or compartments, and
so be protected from contact with air which is
questionable. If a separate room is provided,
suitable ventilation should be secured for carrying
off steam, and the opening for the admission of air
should be so protected that the incoming air will
be filtered.

Since it is difficult to clean and sterilize metal
covers for coolers, it seems more desirable that the
milk be protected by enclosure in separate rooms.

The complete sterilization of this open type of
cooler is a rather difficult matter. The reason for
this is that the cooling surface cannot be subjected
to the action of steam under pressure. The usual
method employed is to direct live steam from a

*Bul. 409. N. Y. Agricul. Exp. Sta.
158

FROM THE PRACTICAL VIEWPOINT |

hose against the outer surface of the pipes, after
the washing has been completed. It is well known
that steam when relieved of its pressure rapidly
cools, and a person can hold his hand a short
distance from an open steam pipe with no incon-
venience. It often happens that not all the parts
of the cooler receive the benefit of even this re-
duced temperature. The tubes, of course, must
be empty of the water usually contained in them
before they are steamed. |

It might be feasible to provide covers for these
coolers which would be sufficiently tight to allow
the pressure of the steam to be retained to some
extent before it escaped into the outer air. Some
covers are now made which are fairly tight.

The best way to sterilize this form of cooler is
to have the tubes of sufficient strength so that
steam may be admitted on the inside under pres-
sure. In such case the sterilization is from the
inside. If, while the pipes are hot from the en-
closed steam, water is allowed to trickle over the
outside, this is heated, and is itself converted into
steam, which helps to cleanse the pipes.

Care should be taken to be assured that the
steam which rises from the milk while being cooled

159

THE PASTEURIZATION OF MILK

does not become condensed upon any unclean sur-
face, such as the ceiling or a metal covering over
the cooler, and from thence fall back into the milk.
If this occurs, very serious contamination may
result.

Open pipe coolers should not be made very long
in relation to their height. It can be seen that
the water flowing through long pipes will become
warmed on the inner surface of the tubes, while
the central more rapidly flowing core may still be
cool. More effective cooling is obtained where this
milk flow is broken up by frequent turns as the
water is returned from one pipe to another.

Second: The cooling may be accomplished in
the same apparatus in which the milk is heated
and held. This can be done when the tank sys-
tem of pasteurization is employed, as illustrated in
Figs. 12, 138, 14, 14-B, 15, 16. When cooling is so
carried on, the cold water or brine takes the place
of the hot water in the pipes, by means of which
the heating was originally done. It is found in
practice that when the same coil is used for the
brine as well as for the hot water, there is dan-
ger that careless workmen may allow the brine and
the water to become mixed. There is therefore a

160

FROM THE PRACTICAL VIEWPOINT —

loss of brine. Some heating tanks are now made
with double coils, one of which is used for heating
and the other for cooling. If the cooling is done
in tank pasteurizers there is the advantage that
the milk comes in contact with no additional metal
surface or other material after it is placed in the
tank till it is drawn into the final containers.

The principal objection to the tank cooling is
that usually a long time is required to reach the
desired low temperature. As stated in the chap-
ter on heaters, the time is frequently from an hour
to an hour and a half. Large coils and a rapid
circulation of brine will decrease this cooling time
greatly.

In country plants at a distance from the point
of milk consumption, the time of cooling is an im-
portant consideration from the dealers’ point of
view, since the time between the receipt of the milk
from the farmer and the departure of the milk
train is limited.

The change in temperature from the high heat
necessary to pasteurize the milk to the cold re-
quired for rapid cooling produces a considerable
strain upon the pipes of the coils, and the joints
are apt to become weakened.

161

THE PASTEURIZATION OF MILK

Third: The tubular cooler is being used to a
considerable extent. In this form of cooler the
pipes through which the hot milk flow are en-
closed by other pipes, through which cold water
is forced in a‘ direction opposite to the flow of
the milk. These coolers are exactly similar to
the tubular heaters illustrated in Figs. 7, 10,
and 11.

This form of cooler is effective and rapid; it has
this advantage, that sterilization by steam under
pressure can be made complete. There is the same
difficulty in emptying the tubes which was noted
in describing the tubular heater and holder, and
whatever advantage there may be in exposing milk
to the air in order to get rid of bad odors, ete., is
absent from the tubular cooler. |

The regenerative principle is made use of in the
tubular heater and cooler, as already described,
and there is little danger of the milk becoming
contaminated by leakage of the water, since the
joints of the water pipes do not come in contact
with the joints of the milk pipes.

One of the most efficient forms of apparatus to
use from the point of view of economy of heat
units is probably that shown in Fig. 11. The

162

FROM THE PRACTICAL VIEWPOINT

great amount of piping, however, renders it diffi-
cult to keep clean.

Washing of Containers

It is of course important that containers in
which pasteurized milk is placed shall be thor-
oughly cleaned and sterilized. There can be little
advantage gained in the proper pasteurization of
milk if it is to be immediately placed in contain-
ers which are not free from all dangerous bacteria.
The relative importance which the cleaning of cans
and bottles has in the bacterial content of milk
has not been recognized to the extent which it
deserves.

Cracks and open seams, especially in milk cans,
may harbor particles of milk which are heavily in-
fected with bacteria, which in many cases are of a
type which are difficult to destroy by ordinary
methods. Especially is this true if the cans or
covers contain moisture, since this aids in the de-
velopment of the bacterial life.

It is undoubtedly true that the methods em-
ployed in washing bottles are generally much more
satisfactory than those in use in handling the cans
and covers. Bottle-washing machines of various

163

THE PASTEURIZATION OF MILK

makes are on the market which perform excellent
work. Some of these employ revolving brushes,
which are automatically forced into the bottles, in
which a strong washing solution has been placed.
In others, the cleaning is accomplished by inject-
ing under high pressure jets of washing solution
into the inverted bottles. This type of machine is
that which is in the most general use at the pres-
ent time.

As usually constructed, this washing apparatus
is a long machine, in which are placed several
tanks for containing the washing and rinsing
fluids. One tank contains a strong washing solu-
tion, another contains water for the first rinsing,
and a third contains clean water for the final rinse.
Over these tanks are placed plates having a sur-
face area of about the same size as that of the top
of a bottle case. These plates are perforated, and
powerful pumps force the liquid in the tanks
through these perforated plates in such a way that
the liquid is forced upward into the bottles, which
are inverted in cases over them. An automatic
feed pushes the cases from plate to plate along a
track made for the purpose. The bottles thus get
first a cleaning with the fairly hot washing solu-

164

FROM THE PRACTICAL VIEWPOINT |

tion, then a rinsing with hot water, after which
clean water is forced into them, which is near the
boiling temperature, and sometimes a final jet of
live steam is forced into the bottles. If the final
rinse water is clean and hot, and the steam is ap-
plied long enough, the bottles leave the machine
at a temperature of from 150° to 170°, and are
reasonably free from bacteria.

Several points are to be borne in mind in using
a machine of this kind. In the first place, no ma-
chine can be depended upon to fully clean an
extremely dirty bottle, particularly those which are
returned from the bottle exchanges and the dumps.
Such bottles should first be washed by hand upon
revolving brushes, where they can be clearly seen
by the workman. They should then be washed again
in the regular jet-washing machine. Another im-
portant point is that the perforations in the wash-
ing plates are liable to become clogged either with
particles of dirt, or with rust, or it may be with
deposits which are thrown down from water which
is very hard. If these openings are stopped up
it will mean that some bottles are not washed as
it is intended they should be, and dealers may be
unable to account for an unusually large number

165

THE PASTEURIZATION OF MILK

of dirty bottles which they find from time to time
upon their routes.

Another important item is the temperature of
the rinsing water. Unless this temperature is con-
trolled by a thermostat, it may be easy to care-
lessly let the temperature drop below the steriliz-
ing point. Workmen who have to take away the
washed bottles from the machine and store them
find that it is uncomfortable to handle bottles which
are extremely hot, and these men may, therefore,
allow the steam supply to the rinsing tank to be
cut down to such an extent that the bottles do not
get sterilized. A thermostat attached to this
rinsing tank will automatically keep the tempera-
ture up to the desired point. If, in addition to
this, a temperature recorder is also attached to this
tank, a record will be kept which a dealer may
keep on file as an office record. This will enable
him to keep in closer touch with the work which
is being done in his washing-room.

Another important matter is to make sure that
the water which is used for the final rinse water
is fresh, clean water, and that it is not used over
and over in the final rinse tank. Most of the
newer machines are so arranged that the water

166

FROM THE PRACTICAL VIEWPOINT

which is forced into the bottles for the final rinse,
instead of falling back into the tank from which
it is pumped, is carried back into the tank behind
it. From here it can be properly used for the pre-
liminary rinsing of the bottles. The use of fresh,
clean water for final rinsing is somewhat expen-
sive when a public water supply is used, and also
a good deal of steam is required to heat it, but in
order to obtain sterile bottles it is necessary. For
heating this water use can be made of the exhaust
steam from engines and pumps, and thus heating
expenses may be cut down.

There is one form of automatic washing ma-
chine in which the bottles which are being treated
are forced down into successive tanks of water, and
the inverted bottles are pushed over fingers from
which water is forced in a direction somewhat
tangent to and also at right angles to the inserted
finger. ‘The water as it is forced into the bottle
has therefore somewhat of a scouring action. This
is of advantage in removing dirt which has ad-
hered to the glass. In this machine, also, the
water which is used for the final rinse is heated
under pressure, and as a result, when it is forced
into the bottle, its temperature is frequently above

167

THE PASTEURIZATION OF MILK

the boiling point. One feature of this machine
is unique. ‘The machine is so constructed that,
when the final rinse water falls below a definite
temperature, of say 180°, it refuses to operate,
since the bottles will not be lifted from the rinse
tank, but will remain submerged. The machine
thus becomes its own thermostat. This effect is pro-
duced in the following manner: The platform
upon which the cases are placed, and by means of
which they are lowered into and lifted from the
rinsing tank, is so counterbalanced that when the
bottles are full of water the weight is too great
for the case to be lifted. If the water which is
forced into the bottles is hot enough so that as re-
leased from pressure it is converted into steam,
then the water is forced out of the bottles, and they
have sufficient buoyancy to enable the counter-
weight to lift the entire case out of the tank.

The older method used in washing bottles, even
when large quantities were handled, was to pro-
vide means for soaking the dirty bottles, then to
wash them by hand on revolving brushes, and
finally to sterilize them in separate rooms, or in
tanks into which live steam was discharged for a
considerable time. ‘This method is still in use to

168

FROM THE PRACTICAL VIEWPOINT

a considerable extent and is effective, but is more
expensive than the machine method. This added
expense is principally due to the amount of labor
involved in the many handlings of the bottles
which is necessary. Various soaking machines are
in use. Some of them are so arranged that it is
not necessary for the workmen to put their hands
into the soaking solution, since an endless con-
veyor carries the bottles into and out of the soak-
ing tank. The solution is made so strong that all
foreign matter, even the bottle caps, is disinte-
grated. After being removed from the soaker, a
rinsing by means of a machine which forces hot
water into them renders them sterile.

Some method of thorough hand washing with
subsequent careful sterilizing probably gives bet-
ter results than does machine work, provided the
men who do the washing are careful to see that no
dirty bottles get by them. This is an expensive
method of cleaning bottles.

Whatever method of washing is employed, care-
ful attention should be given to proper inspection
of the washed bottles. Probably no one thing can
do more harm to a milkman’s business than for his
customers to frequently find bottles which have

169

THE PASTEURIZATION OF MILK

dirt adhering to the inside of them. Even though
the dirt may have been sterilized by the steam
treatment and be therefore harmless, the custom-
er’s sense of cleanliness is offended and the dealer
may lose his trade.

A practice which has been adopted by some
dealers commends itself to the careful milkman.
This is the practice of restirilizing the bottles after
they have been inspected and all dirty ones re-
moved. Any contamination which may have re-
sulted from the handling of the bottles by the
workmen will thus be remedied.

After treatment, washed bottles should be stored
either in an inverted position until they are used,
or else they should be protected by suitable cov-
ers or by placing them in separate rooms where no
infection can occur. If a cold-storage room is
provided, for the washed bottles, there is a cer-
tain advantage. When it is remembered that the
mass of glass in a milk bottle nearly equals the
mass of the milk contained in it, it can be seen
that if the bottle is warm, before it is filled, the
temperature of the milk will be raised to a con-
siderable extent. When empty bottles are stored
at room temperature in the summer, they may

170

FROM THE PRACTICAL VIEWPOINT |

have a temperature of 65° to 70° when the milk
goes into them. If milk is cooled by the cooler
no lower than 50°, it will, by coming in contact
with the warm bottle, be warmed to a temperature
of from 55° to 60°. Bacteria troubles may fol-
low, especially if the cases of bottled milk are not
immediately iced, or if they are placed in a cold
room without ice being placed in contact with the
bottles.

It is a known fact that milk either in cans or
bottles will be very slow in cooling if the con-
tainers are placed in dry air, even though the tem-
perature of the air is considerably below that of
the milk. Milk containers, however, which have
ice placed upon them, will become cooled in a short
time. :

Dealers and others have not realized to what an
extent unclean cans and covers may, and in fact
do, affect the bacterial content of the milk. Un-
til comparatively recently, no effective can wash-
ing, sterilizing and drying machines have been
placed on the market, and even now comparatively
few milk dealers are using them to the extent to
which their merit entitles them. It is usually found
that in milk-handling plants, both in those where

171

THE PASTEURIZATION OF MILK

the milk is pasteurized and in those from which the
milk is shipped in the raw state, the sterilizing is
very inadequately done. Usually the cans are
washed by hand with a brush, and are then placed
over a single jet of rinsing water and then over a
single jet of live steam. The time occupied in
both rinsing and steaming is usually but a few
seconds. It often happens that the can covers are
not steamed at all, but are simply rinsed in water
which is not over clean. When the cans which
are to be returned to the patrons are washed, the
steaming which the cans receive is so brief that it
is almost negligible. This is not altogether the
fault of the man who is washing the cans, for
when milk is being delivered rapidly to the plant
there is little time for long steaming. As a matter
of fact, the cans require a more careful cleansing
and sterilizing than do the bottles, since they are
more likely to contain crevices and uneven sur-
faces than are the bottles. If for any reason it is
not feasible for a dealer to install an automatic
can washer, it is still possible to obtain satisfac-
tory results. An apparatus which is comparatively
inexpensive may be constructed by providing a long
table or runway of iron plate on which there are

172

FROM THE PRACTICAL VIEWPOINT:

installed two or three jets of water for rinsing cans,
and also three or more jets of steam. Each jet
should be provided with an automatic valve which
will be opened by the weight or pressure of the
can as it is placed over the jet. If flanges of iron
or sections of gas pipe are so attached to the table
that they will engage the flare of the can mouth
as it is inverted over the table, it will be impos-
sible to remove the can until it has travelled entire
length of the table and has thus received the
influx of water and steam from each of the jets.
It is possible to so arrange the table that both
cans and covers will be treated at the same time on
the same table. This is accomplished by install-
ing two sets of gas-pipe guides, one of them to
hold the cans in place and the other of them to be
just above the covers as they are pushed along the
table, with the open end down. The cans referred
to in this connection are the standard forty-quart
cans used most largely in the East.

Various machines are on the market which are
so arranged that the cans, after having been well
steamed, are also dried by means of a blast of
heated air. This drying is important for two
reasons. First, because the moisture which may

173

THE PASTEURIZATION OF MILK

be left in the can renders the condition favorable
for the growth of bacteria which have escaped de-
struction, and second, because cans which are not
dry are much more likely to become rusty. Rusty
cans are hard to clean, and frequently become a
loss to the owner because they soon wear out and
are discarded. One form of can rinser, steamer
and dryer is rather ingeniously arranged. The ex-
haust steam, after having been used to operate a
turbine-driven fan, is employed to sterilize the
cans. The steam pipe which supplies the fan tur-
bine passes in coils through an air chamber, and
thus is used to heat the air which is forced by the
fan into the cans after they have been sterilized.
There is thus a very economical use of the steam,
and the apparatus is also very compact.

Cans, after they have been treated, should be
stored in an inverted position until they are used
for containing milk. If, however, they are thor-
oughly dry, there seems to be no objection if the
covers are tightly placed upon them and they are
then stored without inverting.

In determining what test to apply in order to
ascertain whether or not milk containers are ster-
ile, or sufficiently so for practical purposes, it

174

FROM THE PRACTICAL VIEWPOINT

should be remembered that we are not dealing
with laboratory conditions, and that therefore ab-
solute sterility is not necessary, however desirable
it may be from a theoretical standpoint. Our milk
itself is not sterile, and if we can be assured that
the containers are sufficiently clean so that they
will not add any appreciable amount of bacteria to
the milk, and that those which may be added are
not of a pathogenic character, then health authori-
ties should be satisfied. Remembering that a quart
of milk contains about one liter of fluid, or 1,000
cubic centimeters, it seems reasonable to allow the
washed bottles to contain 1,000 bacteria. This
would add but one bacterium to each c.c. of milk
contained in the filled bottle. In like manner,
40,000 bacteria in a washed can might add the
same amount of bacterial contamination to the
forty quarts of milk contained in the filled can.
If none of these were of the coli group, it is proba-
ble that no danger would result. As a matter of
fact, with methods of cleansing which may be easily
secured, the bacterial content of the containers will
be much less than the allowable amount above re-
ferred to.

175

THE PASTEURIZATION OF MILK

Bottle-Filling

The filling of the bottles is more an economic
problem than a sanitary one. Of course, the care-
ful cleaning and sterilization of the apparatus is
necessary, no matter what kind of filler is used.
Any failure in this respect may cause the milk to
gather up bacteria while it passes through the
bottling machine. This may cause annoyance, at
least, when tests are made which indicate a high
bacterial content. If, however, the cleaning is
earefully done, the items which most interest the
milk men are the questions of expense and of efli-
ciency in operation.

If a machine is operated by hand power, there
is the question whether human power is cheaper
than machine power. If automatically operated
by outside power, either electric, steam or hydrau-
lic, then the matter of bottle breakage, case dam-
age, and loss of milk from broken bottles is an
important consideration. A power-driven machine
may or may not be slower in operation than hand
power. The conditions surrounding each plant
must be considered and decisions made in accord-
ance with them.

176

FROM THE PRACTICAL VIEWPOINT

The rotary filler and capper is coming into quite
extensive use, with many features about it which
appeal strongly to the milkman.

Bottle-Capping

It is important that milk, after having been
pasteurized, shall not be recontaminated in any
way. If containers are properly cleaned, the great-
est danger of such reinfection lies in the practice
of capping bottles by hand. When this method of
capping is employed, the caps are frequently kept
in open boxes beside the bottling machine, and they
are sometimes kept in the pockets of the workmen
who are capping the bottles. There is thus con-
stant danger that the caps will become infected by
dust in the air, by milk which is spattered upon
them or by means of the hands of the persons who
handle them. Men who handle bottle cases and at
the same time work about machinery cannot easily
keep the hands clean. The milk caps then suffer.
If any germs of disease are about these employees
then the danger becomes apparent.

Some form of capping machine is desirable. Sev-
eral such are on the market, and many of them

177

THE PASTEURIZATION OF MILK

are doing satisfactory work. It is not necessary to
describe the characteristics of each. Those are
most desirable which fulfil the following conditions:

First: The caps used should be stored in sterile
containers or tubes before they are inserted in the
machine.

Second: A very small percentage of the bottles
should be missed in capping.

Third: They should be so constructed that they
can be readily taken apart for cleaning, and they
should have no concealed pockets or spaces where
milk is likely to collect and become sour or decom-
posed.

_Fourth: They should be strongly constructed in
order that they may stand without breakage or dis-
arrangement, the rather rough usage to which they
are subjected.

It is very desirable that milk bottles be sealed
after they are filled. By sealing is meant that
they be so protected that they cannot be opened
without the fact being readily detected by the con-
sumer. The desirability of this sealing process
gets its force from two reasons:

First: To prevent the drivers or others from
opening the bottles and adulterating the milk.

178

FROM THE PRACTICAL VIEWPOINT.

Instances have been known where the drivers of
rival companies have opened the bottles belonging
to their competitors, and have fouled the milk in
order to cast discredit upon the milk delivered by
the rival concern. Other drivers have taken cream
from the tops of bottles, and have filled the bot-
tles with water. The cream they have sold for
their own profit. Bottles which were effectively
sealed could not be treated in this way.

Second: To prevent possible contamination of the
milk by means which are unintentional. The use of
the usual paper plug cap leaves a space above the
cap where dust and dirt and ice water from melt-
ing ice, etc., can collect. Unless this is carefully
washed off before the bottle is opened, it is likely
to fall into the milk. If a bottle of milk which
when filled has a temperature of say 50° to 55°
is then placed in a case and covered with ice, the
milk is cooled to perhaps 35° to 40°. This causes
the milk to contract. The air in the space above
the milk also contracts, and a suction is thus cre-
ated. The water which collects on the top of the
cap is then drawn into the bottle around the edge
of the cap, taking with it some of the dirt which
may have collected there.

179

THE PASTEURIZATION OF MILK

The drivers of retail delivery wagons who han-
dle the reins, care for the horses and then in de-
livering milk grasp the bottles by the neck, are
particularly likely to leave some dirt or contami-
nating material upon the lips of the bottles over
which the milk will be poured. Serious infection
may result. Caps which are real seals and which
at the same time protect the neck and lips are on
the market, but are rather expensive. They are
used by dealers upon special grades of milk, such
as Certified, Grade A, etc., but are as yet too costly
to be used upon the lower or common grade of
market milk. A great many attempts have been
made to devise a safe seal which shall be protec-
tive and shall be inexpensive, but none have been
very successful. A fortune awaits the man who
can produce a satisfactory seal of this character.

Paper Bottles

For fifteen years or more various sorts of paper
milk bottles have been upon the market. They
have been made in various forms. Some were
made of pulp which was formed into the shape of
an ordinary bottle. Some have been crimped into

180

FROM THE PRACTICAL VIEWPOINT |

a bottle form from a single sheet of heavy paper.
Others have been made of heavy waxed paper,
through which the cream was visible. Some have
had straight parallel sides. They have been made
round and square; have been filled from the top,
and have been filled from the bottom, but the suc-
cess which has attended them has not been very
marked, especially in the East. There are some
firms in the western part of the country where
their use has been rather extensive and where seis
are said to be satisfactory.

The objections to their use has been—1st, the
expense. They are more costly than are glass
bottles, when it is considered that the glass bottle
is used repeatedly, while the paper one is used
but once.

2nd. Many of them are not strong enough to
endure the heavy icing and rough handling to
which they are subjected.

3rd. Customers have been accustomed to seeing
the cream in the bottle, and object to bottles where
the cream is out of sight.

4th. The constantly increasing cost of paper
renders it questionable whether the equipment for
using paper bottles may not prove to be available

181

THE PASTEURIZATION OF MILK

for a short time only, and its expense thus
wasted.

5th. There is always uncertainty concerning the
cleanliness of the bottles as delivered by the manu-
facturers for use, and also as to whether or not
the material used in the paper may affect the milk.

There are undoubted advantages in the use of
the paper container, among which are:

Ist. That the expense of handling and trans-
portation will be lessened, on account of the lesser
weight of the paper.

2nd. The expense of washing returned bottles
will be saved, since the paper container will be
used but once.

3rd. The possible danger which exists through
the return of bottles from the public dumps, and
from houses in which there are communicable dis-
eases will be lessened if the single service container
is used.

4th. The danger from broken glass, which occa-
sionally finds its way into the milk, will be ob-
viated, and the wounds which are inflicted by
broken bottles upon workmen who handle and wash
them will be prevented.

182

FROM THE PRACTICAL VIEWPOINT

Home Pasteurization

Many physicians who thoroughly believe that
milk should be pasteurized for infant feeding, also
recommend that this pasteurization be performed
in the home, and that the pasteurized milk be
fed as quickly as possible after the heating is
completed. This method eliminates the possibil-
ity of recontamination which may occur when milk
is handled under commercial conditions, and it also
insures that those bacteria which are not destroyed
during the pasteurization process will have little
opportunity for growth and increase between the
pasteurization of the milk and its consumption.

It is not the purpose of the writer to here de-
scribe the various methods employed for home pas-
teurization. Such information may be obtained
from the pamphlets which are distributed by those
responsible for maintaining the various infant-feed-
ing stations located in our cities. Some of these
stations are maintained by the municipalities and
some by private individuals. Dr. Rosenau, in his
book on “The Milk Question,” discusses this phase
of pasteurization quite fully.

Whatever method of home treatment is employed,

183

THE PASTEURIZATION OF MILK

care should be taken that the heat is high enough
and is maintained for a sufficient time to reach all
parts of the milk, and so kill the pathogenic bac-
teria. The heating medium should not be hot
enough to cook or change the chemical characteris-
tics of the milk or to impart to it a disagreeable
odor or taste.

184

CHAPTER VI
EFFICIENCY OF VARIOUS APPARATUS

During the writer’s experience in the actual
operation of pasteurizing plants, a great many sam-
ples of milk have been taken which have been ex-
amined for their bacterial content in order to de-
termine the efficiency of the various pasteurizing
plants in the destruction of bacteria. These results
have been tabulated, showing the bacterial content
before, during and after pasteurization. In these
tables the kind of apparatus are indicated by fig-
ures only, no name of apparatus or of the manu-
facturers being given. The dealers at whose plants
the tests were made are indicated as “A,” “B,”
“C,” ete. Thus at a plant operated by dealer
“A,” for instance, a heater illustrated by Fig. 00,
a holder like Fig. 00, and a cooler like Fig. 00 may
have been employed.

Lest the reader be misled as to the efficiency
of certain definite forms of apparatus, and lest cer-
tain manufacturers be led to feel that results ob-
tained have failed to give justice to the apparatus

185

THE PASTEURIZATION OF MILK

handled by them, the reader is warned that effi-
ciency tests are sometimes misleading. It should
be remembered that at least four factors enter into
the causes which produce the effects indicated.

Ist. The character of the apparatus itself.

2nd. The carefulness with which the plant is
operated by those responsible for it.

3rd. Whether the apparatus is thoroughly
cleaned and sterilized.

4th. The character of the milk treated.

It is, of course, understood by all those familiar
with bacteriological work that these are factors of
error in the results which can never be entirely
overcome.

If apparatus is so constructed that the heating
and holding and cooling are true to their indicated
capabilities, then the results will be good—if the
machine is properly operated and if it is clean.
These factors being reliable, the results can be
taken at their face value if the milk is of normal
quality and does not contain, we will say, certain
forms of bacterial life which are difficult to destroy.

When results are good, it undoubtedly means
that both the apparatus and its operation are sat-
isfactory. If the results are bad, it is not always

186

FROM THE PRACTICAL VIEWPOINT -

easy to say whether the machine, its operation, or
the milk is at fault.

In regard to the milk itself, there are many fac-
tors which must be taken into account when de-
termining the efficiency of any apparatus. Esti-
mates of machine efficiency based upon the
percentage of bacteria destroyed are frequently
misleading. It can be readily seen that if the bac-
terial content of the raw milk is high, any good
pasteurizer will kill a large percentage of the
germs in the milk. For instance, if the original
milk contained 5,000,000 bacteria per c.c., and
after being pasteurized contains 100,000 bacteria,
there would have been a reduction of 98 per cent.
of the bacteria in the original milk. Milk contain-
ing 100,000 bacteria per c.c. would not, however,
be considered to be an entirely satisfactory prod-
uct to place upon the market, especially if it con-
tained organisms of the coli type.

Again, let us suppose that the original milk con-
tained 10,000 per c.c., and that by means of the
pasteurizing process this number was reduced to
1,000; such a milk would undoubtedly be a proper
milk for consumption, although the percentage of
reduction had been 90 per cent only. It is there-

187

THE PASTEURIZATION OF MILK

fore plainly seen that the efficiency of pasteuriz-
ing machinery, when expressed in percentage re-
duction of bacteria only, must be taken with a
great deal of reserve. It is necessary to know the
character of the raw milk, and also to know if coli
types are all destroyed. In speaking of the de-
struction of coli, it should be remembered that
germs of this group are not necessarily all danger-
ous. In this connection they are used as indicators
only. It is known that they are more difficult to de-
stroy than are any of the pathogenic or disease-pro-
ducing bacteria. If, therefore, the coli are all
killed, it is safe to assume that no dangerous mi-
crobes remain alive. While, if the coli are present
in the finished product, there is a possibility that
disease germs are also present. It is known pretty
definitely that if milk is heated to 142-145° for
thirty minutes, all coli will be destroyed.

The following tables are compiled from very
many tests made. When these tests were made
there were three or four samples of milk taken at
each point of examination; for instance, four sam-
ples of raw milk were taken at the same time.
When these were examined, the average of all the
counts was determined. In the same way there

188

FROM THE PRACTICAL VIEWPOINT

were four samples taken at the outlet of the heater,
the holder, and so on. In the tables herewith com-
piled, only the average counts are indicated, in or-
der to avoid any bewildering mass of figures. It
should be therefore borne in mind that bacteria
counts here indicated are averages.

In figuring out the percentage of reduction,
the relation between the bacterial content of the
raw milk and the milk as it leaves the holder is
considered. It will frequently be found that the
number of bacteria in the milk leaving the cooler
is higher than when it leaves the holding appara-
tus, and that this number is again increased when
the milk enters the bottles and cans. Usually un-
clean coolers, bottling machines and bottles are
responsible for this increase.

Not all of the types of apparatus which are
illustrated and described in this book have been
tested by the writer as to their efficiency in the de-
struction of bacteria, and any omissions which may
be observed in the tables are not due to any inten-
tion on the part of the writer to slight any of them,
or to any desire to call attention more forcibly
to one kind of machine than to another. It simply
means that the results of tests are not available.

189

OF MILK

THE PASTEURIZATION

. 6% a SF = StL ial 2 0s BCC Amat Acar duay,
%$6' 66 CLE‘6 ose's 0¢3‘T OSS‘TS 000‘0S9‘T «°° ***0°0 sad “yoeg
§31d9g PLE
aieaccaveue = eaiacce «108 9 681 olS1 obF ye ar orececass 0°
LG 6 OOL‘S 0083 OSI‘T PSLEI eoscle er °0 god “joeq
satlag pug
é L¥ a aaaeneie (6ST 388 | een oe ‘dura y,
%SG' 36 Cie. ee *S9 008 O0S: See od Jad "yor
uorjpNpsy jo sapqyog Jsjooy JoploFY = dJoyzeoRy STN $avlag 78]
ose UI010g uy wmoLy LC A | Woy MOY
Il ‘Sq stale; mub/\e. b..8 6 ereNelele@, 6.9 aie, 6) 6.6. ce ele. a ete ae mC) Coleg)
08 1 As | we) e668 es a lale, 6. ple 8: ieee cee: eeve here ué"eoao we ts JoploH
(pegrpoun) a re A § weld hak ata Nane, @ ue. ee dumle (6) uae eee: si eece e008 ete ReMUE) 8 |

«Vs UTIVAC AO INVId ONIZIYNALSVd

o

19

FROM THE PRACTICAL VIEWPOINT

oL® o9F 9 OFT eevee o8F ee duay,
%I18 00s‘ OST Oe. ee OSL o°0 Jad “yoeg
SOLOS Pas
0 OF 00% o FFL = eee |) aceasta et Si. dua,
%1L'86 99F'E 008 995'T --00FL = 999°L6 o°o Jad “yoeg
' slag pug
o0F 088 061 ERE. wh oto reat eee dua,
Ys" 66 O1‘6F O09TI 008 oss‘¢ oos‘98T O70 tad re
moIpNpey jo s9}j0G JOO JOpPfOFY = JozeoTT AMAL $aVsag IST en
288] U9010g Uy WoL mol] MoLy MEY
EE “BI e | ee J9J00R)
03 Fl asf ed JoppoH
rs "SI ci J2}v0F]

«fH, UAIVAG JO INVId DONIZIYNALSVd

OF MILK

THE PASTEURIZATION

i + . : OF - Stl és CFI - OF Curt eriercac) «Ot ta dwmoy,
%LO' 66 OSs *F O9F 0063 00908 O0S*LIS ""' 9°90 Jed "yoeg
S919 PUG
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%bl 66 00¢ OST 009 00s9 oos‘éol “""""" 9°90 Jed *yoeg
moIpNpsy jo sayWog JejooD Jepjoy, = JoyvoRT SIMA 891d9G IST
ose UI0I0g uy WO1 W101] WO1 MOY
Il "Si PS et ee ea al te ee te Peseta re ee eS ae ae NE Tat a, J9]00)
03 ‘Sly Sc 5X) (ST eLeHAe GOL a ss eee, alee eens Ah ew eles JoplOH
7 si Ce REMC) 8 |

«Js UAIVAG JO LNVId DNIZTHOALSVd

192

FROM THE PRACTICAL VIEWPOINT

oft 08h oft oSbl DF iiaiwle C568 one: anise duray,
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sawagy pug
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%9eo’ 96 009TL 00F'9 0086S 009°L89 O00‘9ST® «****" oo rad “qoug
Fa no ay EE SY SAE ROT EL oe CREAN DN STE AMEE ASIEN BS Dien
dorpnpey Jo sayj0g = JOO )§=6DpORR «eIVOR YN Saray 1ST
938100019 g uj wo1g mol wOd, MBY
€& 1 € | oe ere eee meee rere eee ees ee ereseese Iajooy
(yuR} 19) TA i ts | eee ees eer ee ere r ees eeeserereesene JoploH
rsd "BL ee ee 19} eof]

«Gd, HAIVAd FO LNVId DNIZIYNALSVd

193

OF MILK

THE PASTEURIZATION

o0¢ 0 0G 9 09T SOL 5 OF mies Mabeebecey (05 |p

°%86' 66 oor’s 00t 00 000 O00°¢9§ °°°** ‘90 Jad “poRg
suey saiiag uit
o SF oS? o SFI o IST oP aC CLA rs rer ° ‘duay,
PS’ 66 o0r‘'¢ 009°E 008 008‘SL O00FLT °° °° *'9'0 sad ‘yoeg
sawag pg
ofF eel ce ok¥E GiGi sictg-c Ue roetceas <P 8 oe *dutay,
%L6° 66 oos‘oL o008‘¢ 000‘L OSO‘9T O000°00FL °°" oo Jad *qoeg
Saag pug
oSP olF o SFL (0ST o8P Se aniaicaie io ueniniianese lin dua J, =
%68' 66 0S3‘9T 000°L 000‘0L 008°93L 000‘Sss‘s “°°” ‘o'o gad “peg
TOTP N psy jo s9f}0g nt) (elel@) Jop[OF 19}C9 FL FAL sailay ST
988}U9010g uy WOL yy mol HL mol cI MEY

SoNUIUA OF ‘9WI} SUIP[OHL

68 “BI Ser anemoneienensWarieneMeceaeheNede- (sua tngia's iofaite ne Gas *Jgjoo)
£S ‘BIq GeO SO MORCMORT tt Gas OSE DAD VE) ACCT OL ce PDE EN atitet JOp[OH
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«<a, UAIVAG JO LNVId DNIZIUNALSVd

FROM THE PRACTICAL VIEWPOINT

° PP ° oP ° PPL ° SFI
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ne ae of91 oPLI
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oF eee es
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5, bee sot 242%
%13° 6 091s tel Sl | RE aa

UoIpNpey jo sopj0g
23%}U9010q uy

JaJ00D
wOo1y

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mol

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SoyNUIUA Gg ‘aUIIT} ZUIploF]

bi Paes os ose
3 ‘sigs °c: Risen? Rue ee

TG ee eS ee

089 acetal talasio! | 5:1
000‘SEI STC YL rod ‘peg
saLlag yg
o bh sete eereateti ad 8h. 5 2
000‘6S3 Sashtesieat gery aad *‘qoeg
sawag Ynt
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000‘89T cee eae 2°20 rod ‘peg
891lag plg
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000‘883‘S see eee yt) rod ‘peg
eae PUR
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THA satay IST
MEY
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OF MILK

THE PASTEURIZATION

339 E ¢ LP 4 LPL . SFL : eae Baka ee dutay,
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uorpnpey jo seqoqg JfooD JepjpoRH = 10} BOF] SIAL savlag 187
238} U9010q ul WoL] WoL wooly MBY
IL st eee er eee eee eee eee eee eee sere eresere IajooD
13 rol | er er ee ee Jop[poH
IL rl | eos ee ere ee eee er eee e eee eee eee eeeee Rea) 8 |

«D,, HATIVAdG AO LNVId ONIZTYNALSVd

196

FROM THE PRACTICAL VIEWPOINT

o8P o8P o PPL eee ee o8P Cle CPs ei eles 8 i 0

%1s' 66 C38‘L . OOF ee eee 0008S Bias, Nera ayers qod ‘qorg
sarwag yIy
o8F o8P o PPL ce «6 o fF cece eee Sey,
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89a Y PLE
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sardagy pug
obP o PP o9SL 0 OFL 0 SP ew eve Wak “net is S
%8l'S6 0008 000°08 008‘8 000‘00L 000°03T °“""** ‘oo god “yoeg =
————————————— Eee
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Aep Joy snyeredde y3no1mqy yt ysI1q

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«H, UAIVAG dO INVId DNIZIMNALSVd

OF MILK

THE PASTEURIZATION

o vb oF o 861 oOFL 086 :
%1¢' 86 o°s*6 00SFL = 00rF Oc6'L¢e 000°S63 ~

uorjeiedo ZuLmMp J97e] Yue} Ysnosyy Suissed FIP

o0F . 988 oOFL ofFl 0 8& :
%Iv' $8 00V O¢L'T oos'zg 006% o0csss -

SOMUIUL YF ‘9UI} SuIP[OFT
Aep 10} yu} Ysnoiy} Suissed yO 4s11 7

o6¥ olP 066 oOFL o9F
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o 8¥ o9F o 61 oOFL of¥ ;
% 63° $6 ooo'Tss o008s‘s 000°ZT 000°28 000°SS6 -

Siig. homoge ‘duay,
+++ e99g god “peg

savdagy 474

ee eeee eevee ‘dway,
‘+ s999 rad peg

sa1ag pag

re ‘dua y,

Sapa 9°90 Jad ‘~eT co
sauagy pug D>
eee nee cesar dura y,

doTpNpey jo soyog Joo Joppoy, sJsyeoxY ATW

28e}U9010g ul WOL WoL WO] MEY

SOMUIM YF ‘OUI Surpjloyy

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3 Pd A | Cee Det iat ee a eee 4 6.0 @ 6.68 eee Aree we JOpjoH
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«Ll, UAIVAd AO INV1d ONIZTHONALSVd

salad IST

FROM THE PRACTICAL VIEWPOINT

088 oP o SPI o PFI o GF C20 Woe ay8 eee ene ie dua,
%08' 86 oss 0OT L9G OOL'SI O9s‘ss “"°°** 9°90 Jod "youg
sadag pug
oft). 6 OF 0081 00ST S|: a a al duay,
%OL' $6 091s CLE‘SL §=— 00 ¢ 008‘9L O00‘°08I °*°°': 0°90 Jed ‘yorg
uorjonpey jo seqjog = Jajoo WploH ss Ao} BOTT IA 8919S 1ST
o3¥]UI0I0g uy TOL WO y WOL MOY
L SI A Stet et it SM UBT iC ior a Ne ein in Oe CR eae Iajooy
S “SI a ee PLS PCO CS? Wa ie os ae Tg oe a JaploH
Z BI ci Pe) SEONG Ou aS S LM Oli ee Bee Tees) wae aoe teeta ielie ce RCRM:C) 8 |

«f,, WATVAG JO LNVId DNIZIMOALSVa

19

OF MILK

THE PASTEURIZATION

o OF 088 o9FI o SFL o9F Nye Ses Se
%¥6 66 003— o00l— 009 O0OS‘LL 000‘638 °°" °° *0'2 dod “yoeg
sodas Yt
SoyNUIUT YF ‘OUI, SuIploFL
oL¥ oP o SFT o OSL ol pe <0 Ras One
%86' 66 490% ¥S6 L9¢'‘T 000°036 000‘Ss9'L ******9°0 rad “yoRg
sa1lag P4E
sSopnUia OT ‘aul SuIplpoH
o9F oP oOFL oLFT o8P See he eT
%86' 66 992°9 099°S OOFT O008‘sIS‘T 000‘S8e"L ******9°0 Jed “youg
eoH0g PUG
oS¥ ol¥ of FL o SFI oh Seas hn ae Q
%L9°96 683 OFS oor oss’s 000‘'8F = °° 0" aad “joug

worpNpey jo sowog JaooQ JoppoyR, = JoVOHY 3A
9389010 q uy WoL] WoL] WO1y MEY

SoyNUIU OF ‘eWty ZUIP[OF{

(OA1}e19UaZAL) rR NS hag a a aa a ace vga attra | (0.9 |
CN Go (ie ieee tne <p: ea eenee ie arene) 80.8) |
TPs fF ONe Se Ate BP ECE TA ele eee

«M,, ULIVAG JO LNVId DNIZIUNALSVd

$91dag IST

FROM THE PRACTICAL VIEWPOINT

obF oFF o MFI o LF oFOT een’? GUST,

%L6° S6 996 OOT‘S 006‘F 00rs O000I9 °° ***‘9'0 Jed “poeg
saiag yit

obG ofS o OFT oSFl o S01 He Satta se dua],

%El° 66 000°StL 00806 000°S6 008‘893 O0S‘Z90°IIT' °°" ** oo Jed “yoeg
saa! Pag

ofS 089 o SFL o MFI SOOL2 ee dua],

%19° 66 009'FS 00003 00083 009°L9 000‘008‘¢ °° °° **"0 Jed *yoeg
sadag Pug

ofS obo o OFT o SFI 9801 ieuptees =>" dw,

%t6' 66 00091 006 0083 00FSS 000‘0FS'S “°° 90 aod “joeg
uorjonpey jo soyog Joop JepjpoxRY = JoyeVOH] ATA sarag IST

988] U9010g uy wWoly WO1 WoL], MEY

SOMUIU YF ‘9UII} SUIP[OH

(aaryei19uasel) 6S cb See ame V6 a. 8 Ot e6 eae Kayes TOO?)
es See hee ann OP ee eae
fo eee eee ewes nner Cy) = |

«I, YATIVAG AO INV Id ONIZIYNALSVd

QR

OF MILK

THE PASTEURIZATION

50S (0S o98l 9681 o8F ores a treo. duay,
%oso' Lh 00L'T 6&9 OOL‘SOL O009°FT O00%L0G “"**" o°0 Jed “joeg
Sa1lagy pug
(0 o6F oLeT (OFT 099 BOER OSTEO Cuan, Oa duay,
% 08" L8 006s sLeT o00s9 o0s's 0086h """""' o°o Jad “joug
uoIjonpey jo seyjog JeJ00ODQ JOppo_, JO NTN SIS IST
ose ]UI010g ul WHOL, WO1 WOI MEY
SOMUIU GT ‘oUIT} SUIP[OF{
cc rod A | Ce Jajooy
(jUe} 19) Ta ‘SL CC a JOp[loH
8 “Bq Pitan Oh Oe eth tet h Ce ONOat eOn Mt hcier trary Om teretyeCier (wcrc Jo} eo FT

«AN, UAIVAC FO LNVWId DONIZTHOALSVd

202

FROM THE PRACTICAL VIEWPOINT

(OF 098 ial o MFT 088 LVI Se Cvs. a! e' extn e ee dua,
%6h 66 009‘S 009‘T 000‘F 000°TS 000‘68L °*°**:9°0 aed -yoeg
sailag yny
o OF 098 0 OF o LPI 088 ais 7 aNwy wire, ear arts ‘dua y,
%O1l’ 66 000‘99 000'F 000‘S 000‘FI o00‘sss “"""** 9°90 Jad “peg
$91IT PLE
5 0¢: 5 OF o LF o SFL 50S ee Le ri ees ‘dway,
%bS' $6 000°F9 0008 O00‘9II O0S‘SIL O00‘9TL‘T °°° °° 0°90 Jad “youg
S9llAd Pug
i<\a)
o8F OFS o SSL (0ST P| Aa a Ee *+*sduray, =
%9S' 86 000‘86 000°S8 00006 000°69 000‘9F¢ °°" *: o'0 Jad "yorg
a er a Se ek
dorpn psy jo s9[}10q Jal[oorn J9p[9oH 19}89HL FATAL satay IST
23809010 q Uy mol wmoly Woody MOY
G ‘Si . om eh Wiese . i e (6\e n6 erie tate) 6) 6.6 “*** "Tajo
88 “BI ag ene @ elle. « 6 \e ee . . o Pe ae "eo 3 we ee we) 8) (0)
c "By . Ew eee a Ce erlaante ee Miah e¥iny wee ere we Joyeo FT

«Ns, HATVAG JO LINVId DNIZIMNALSVd

OF MILK

THE PASTEURIZATION

o9P oS o 881 o SPL olf CSC ae is eae ‘duay,

%+96'66 999 09T 00 000°SF 000‘°9K%S “""*: o°0 Jed “joeg
sa1lag ynt
o8P o SP oLSl ofFL = OF eran Wf
%9' 66 SSP 001 999 0098 00082 °'''' ‘a0 Jed “~oRg
S9UAY PLE
ae eee) pny ea, o SFL o SFL o SP anle R eM (a0 ee te renee duo],
%$' 66 © e.eneite a alte “arte 00S‘I eee ee 000‘°108 a Lg Yr Jod “‘porg
salag Pug
s
pad Cups ee one o SFI (OST oSt Pe eh areca ‘dua y, =
%$9° 66 CR ec SPornCar 000‘T were URE 000‘0L2 oreraevere a) aod *‘qyoeq
uoTjoNpey jo sey}jog Jojooy JepjoxRY = JezyeOH AINA $atLad JST
ose ]Us0I0g uj W017 wmoly WO1 MEY
Gaia: * >? Cat YN) Ove) a nnene be 6 %e.e evesene. le "eee" IQI00D
(S00. T) es Sa ee emake e ee) 8.6 ane? TOOL
re ale i a aol Rn aee've © e 6 0 seve Jo} 80 F]

«O,, WATIVAdG AO INVId DNIZTHOULSVd

FROM THE PRACTICAL VIEWPOINT

50S o OF o MFI o SFI ESL ec he ee ee dua J,
%18° 86 000‘6T 00F SS 000‘8T 000‘901 000‘S60‘T ~°°°** o°0 rod “preg
sawlag Y1h
eee & ol ole o Stl a) Nore ronoees Salata
%96' 66 009‘0L 000‘8 000‘T 008631 000‘0SS‘S °° °° **a°d aad “preg
SII PLE
o9F 088 o OPI o SPL 019 Eel ena teeters ote dua y,
MFI 66 000‘T 000‘F 00¢S 00O‘LT 000°%63 °°" 20 aed “peg
sailag pug
o LP eee o OPI Sebel es dua,
%Sb BS 000‘9SS O000‘0LI 000‘¢8 000°606 000‘S66 “°° "° °0 rod “preg
uorpnpesy jo sei}yog dJajoog JoploH 19 eo] AINA saidag IST
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207

CHAPTER VII

CHANGES IN THE CREAM LINE DUE TO THE
PASTEURIZATION OF MILK

Dealers who have had experience in the pas-
teurization of milk know that from time to time
they have trouble with what is known in the trade
as the “cream line” upon bottled milk. This may
mean that the line of demarcation between the
cream in the bottle and the skim milk just below it
is indistinct and faint, or it may mean that no
cream at all is visible and the contents of the bot-
tle has the same color all the way through. Again,
it may mean that the apparent amount of cream
upon the milk is lessened. Either one of these
conditions is a reason for complaint on the part of
the customers. Dealers are therefore anxious to
obtain as great a volume of cream as possible upon
the milk sold by them, and are also anxious to get
the line of division as distinct as possible. Deal-
ers are sometimes at a loss to know why milk will
at one time show a good cream line, and at another
time, when the conditions are apparently the same,
the cream will be disturbed.

208

FROM THE PRACTICAL VIEWPOINT

In 1914, when the writer was connected with
the New York City Department of Health, the
Board of Health adopted certain modifications in
the regulations which had been in force concerning
the pasteurization of milk. Among these changes
were different rules concerning the temperature to
which milk must be heated and the length of time
for which it must be held at this temperature if
it was to be officially recognized as pasteurized
milk.

Prior to that time, the rules allowed a somewhat
wide variation in the heating temperatures, and a
corresponding variation in the length of time for
which the milk should be held. Thus milk which
was heated to 140° must be held at least twenty
minutes, while milk heated to 158° need be held
but three minutes. Between these extremes other
temperatures and holding times were allowed. This
sliding scale, as it might be called, allowed such a
latitude that milkmen who sold milk in cans only,
and were thus not much concerned with the cream
line, could heat the milk to a high temperature and
hold it for a short time. On the other hand, those
dealers who sold bottled milk, and who were desir-
ous to obtain as great a volume of cream as pos-

209

THE PASTEURIZATION OF MILK

sible, could and usually did heat the milk to a low
temperature and hold it for a comparatively long
time.

A desire for uniformity of methods in the treat-
ment of milk led the authorities to adopt regula-
tions, in accordance with which one standard for
pasteurization only was applied, in all cases when
milk was heated for market use. The rules thus
adopted required all pasteurized milk to be heated
to 145° for thirty minutes.

Dealers who endeavored to comply with this rule
complained that they found the cream line was
affected, and that they could not comply with the
public requirements without injury to their busi-
ness.

In an effort to ascertain to what extent the
strict enforcement of the regulations would affect
the commercial quality of the milk, the writer made
an investigation.

This investigation was not made with the inten-
tion to determine what form of apparatus would
do the best work, nor to make any extended or ex-
haustive tests of any one form of apparatus un-
der varying surroundings and conditions. The ob-
ject was to see if it was possible and commercially

210

FROM THE PRACTICAL VIEWPOINT

practicable to heat milk to 145° and hold it for
thirty minutes with the machines in use in the city
without seriously affecting the cream line. Any

results and data secured do not warrant the con-
clusions that the experiments indicate the essential
superiority of any of the apparatus described.

A little thought on the part of the reader will
make it clear that so many factors enter into the
problem that such conclusions would be unwar-
ranted.

In the same way that percentages of bacteria
reduction mean little unless we possess all the
data connected with the handling of the milk,
so likewise percentages of cream upon _pas-
teurized milk are not alone of ultimate value as
showing that one apparatus is more satisfactory
than another.

A series of tests was made at several of the .
pasteurizing plants in New York City at which
different forms of apparatus were being used, the
milk in these various plants being subjected to dif-
ferent degrees of temperature for varying lengths
of time. Samples of milk were taken to determine
the amount of cream which appeared upon the
bottled product. At the same time, the conditions

211

THE PASTEURIZATION OF MILK

surrounding the handling of the milk were noted
in order to determine if other factors aside from
the temperature and holding time had any effect
upon the cream line.

In making the tests, the samples of milk taken
were set in standard cream gauge glasses and the
actual percentage of cream showing upon the milk
as indicated thereon was carefully noted. These
tests were made during the early part of Decem-
ber, 1914.

First Trest.—The first test was made at a plant
in which the pasteurizing apparatus consisted of
three tanks of the type shown in Fig. 13. Each
tank had a capacity of about forty cans of milk,
and after being filled the milk was heated by
means of a revolving coil of pipe extending through
the tank, through which coil hot water and steam
were forced. After the milk reached the proper
temperature, the steam was shut off in this coil
and the milk was held at the same temperature
for the desired length of time. It was then dis-
charged into a cooler consisting of a tank in which
were revolving disks, which is not here illustrated,
and immediately cooled. Since it required con-
siderable time for the tank to be fully emptied

212

FROM THE PRACTICAL VIEWPOINT |

after the discharge was commenced, it is evident
that a part of the milk was held in the tank for
a considerably longer time than was that which
was first discharged from the tank. In making the
test, one tankful of milk was heated to a tempera-
ture of 142° and was held thereat for about thirty
minutes. The exact time of holding was not as-
certained on account of the fact that the milk was
being discharged from the tank at the time the
inspection began. A sample was taken from this
milk and placed in a cream gauge, which was then
packed in ice and allowed to stand for four hours,
at the end of which time 15 per cent. of cream ap-
peared upon the cream gauge.

A second sample was taken from one of the
tanks in which the milk had been heated to a tem-
perature of 146°, and held thereat for thirty-four
and a half minutes. The sample here taken was
allowed to stand packed in ice for four hours, at
the end of which time 13 per cent. of cream ap-
peared upon the gauge. A third sample was taken
from the same tank, but it was taken from that
milk which was last discharged from the tank.
This milk, therefore, had been held in the tank for
one hour and twenty-three minutes. This sample

213

THE PASTEURIZATION OF MILK

was also set in ice for four hours and showed 8 per
cent. of cream upon the gauge.

A fourth sample was taken from a second tank
in which the milk was heated to a temperature of
146° and held thereat for exactly thirty minutes.
This milk showed 15 per cent. of cream upon the
gauge. |

The method of handling the milk at this plant
should be noted. Milk was poured from the cans
into a dumping tank on the ground floor. It was
then pumped to a small tank upon the third floor
of the building, thence flowed through a centrifugal
clarifier, such as shown in Fig. 32, and then flowed
directly into the pasteurizing tanks.

Seconp Trst.—A test was also made in another
milk plant in which the same form of pasteurizing
apparatus was installed. In this plant, the milk
was pumped from the receiving vat on the gound
floor into a tank upon the second floor, from which
the milk flowed through a clarifier and was then
discharged into a mixing vat, from which it flowed
into the various pasteurizing tanks. ‘The opera-
tion of this plant was similar to that in the plant
previously described, except that, in the first in-
stance, the water which was forced through the

214

FROM THE PRACTICAL VIEWPOINT 3

heating coil of the tank was heated by means of a
steam jet, injecting steam directly into the water
pipe, whereas, in the second instance, water was
heated in a tank outside of the pasteurizing tank
and was pumped, after the heating, directly into
the heating coil, it being the belief that if the
water was heated in this manner there was less
danger of the milk becoming scorched on account
of the water coil having been heated to a tempera-
ture which was excessive

At this second plant the first sample was taken
from the raw milk before it had passed through
the clarifier. This sample was allowed to stand
in ice for eleven hours, at the end of which time
191% per cent. of cream appeared upon the gauge.
A Babcock test was made of this milk and it was
found to contain 3.8 per cent. of butter fat. A
second sample was taken, which was as nearly as
possible from the same milk, after it had passed
through the clarifier. This sample, after standing
for eleven hours, showed 17 per cent. of cream on
the gauge. This milk also contained 3.8 per cent.
of butter fat. A third sample was taken from one
of the pasteurizing tanks in which the milk was
heated to 145° and was held in the tank for thirty-

215

THE PASTEURIZATION OF MILK

three minutes, at which time the temperature was
found to be 142144° F. This sample, upon being
set, showed 12 per cent. of cream in the cream
gauge and contained 3.8 per cent. of butter fat.
The fourth sample was taken from the same tank
of milk, but when the tank was nearly empty.
The milk had been standing in this tank for one
hour and twenty minutes. It had been, however,
cooled to a temperature of 60° F. by means of
cold water pumped through the revolving coil.
A sample of this milk, upon setting, showed 15
per cent. of cream in the cream gauge and con-
tained 3.8 per cent. of butter fat.

_ It was thought possible that the speed of cool-
ing of milk might have an effect upon the cream —
line. Therefore two samples of milk were taken,
one of which had a temperature of 135° F. This
sample was allowed to stand un-iced until cooled
by air contact to a temperature of about 40° F.
The second sample of milk was taken from the
same batch of heated milk, but this sample was
taken after the milk had been quickly cooled in
the cooling apparatus to a temperature of 32° F.
After setting, these two samples showed no appre-
ciable difference in the cream content. ‘This indi-

216

FROM THE PRACTICAL VIEWPOINT

cated that the speed of cooling had little or no
effect upon the rising of the cream in the milk.

The tests made at these two plants indicated
that it was entirely possible to heat milk to 145°
F. and hold it for thirty minutes without materially
affecting the volume of the cream contained in the
bottled milk, and that milk heated to 145° F.
showed the same amount of cream as that which is
heated to 142° F. |

Tuirp Test.—A test was made at another plant
where the same form of apparatus for pasteuriz-
ing was in use. During this test a sample was
taken from a tank in which the milk was heated
to a temperature of 141° and held there for sixty
minutes. This sample, after standing a sufficient
length of time, showed a cream content of 15 per
cent. A second sample was taken of raw milk
which had already been passed through the clari-
fier, and this milk was found to contain 15 per cent.
of cream. A third sample was taken from a tank in
which the milk had been heated to 145° and held
thereat for sixty minutes. This milk, after stand-
ing, showed no cream at all upon the cream gauge.

The results here obtained did not correspond
with those obtained at the two other plants where

mae

THE PASTEURIZATION OF MILK

the same apparatus was in use. No apparent rea-
son could be seen for the variation. Milk at this
plant, as received from the patrons, was allowed
to flow from the weigh vat into the mixing vat,
from which it was pumped to a vat upon the sec-
ond floor, thence it flowed into a clarifier, from
which it was discharged into a large mixing vat on
the same floor. It then flowed by gravity to the
pasteurizing vats on the first floor.

Fourtu Trest.—A further test was made at an-
other pasteurizing plant, in which the milk was pas-
teurized by means of a heater and holder, shown
in Figs. 5 and 22. In this heater the milk was
forced between two concentric cylinders, in each
of which hot water was contained, having a tem-
perature of 159°. The milk while being heated
was kept in agitation by the rapid revolution of
one of the cylinders above referred to. After
heating, the milk flowed by gravity into a series of
insulated tanks, in each of which it was held for
twenty-four minutes. On account of the fact, how-
ever, that milk as discharged from the heater
flowed first into a tank from which the various
holding tanks were filled, and on account of the
added fact that when these tanks were discharging

218

FROM THE PRACTICAL VIEWPOINT

the milk, it flowed into a second tank before being
conveyed to the cooling apparatus, it is probable
that the milk was actually held at the highest tem-
perature for a period of at least twenty-seven
minutes.

A sample was taken from the raw milk before
being clarified. This milk, upon setting, was found
to contain 15 per cent. of cream and to have a fat
content of 3.9 per cent. A second sample was
taken from milk which had been heated to 145°
F., and, after holding, was set and found to con-
tain 1014 per cent. cream and 3.9 per cent. butter
fat. A third sample was taken from milk which
was heated to 144°, and was found to contain 8
per cent. of cream and 3.9 per cent. butter fat. A
fourth sample was taken from milk which was
heated to 142°, and was found to have a cream
content of 8 per cent. and 3.9 per cent. butter fat.

These results indicated that the milk which was
heated to 145° contained a greater percentage of
cream, by volume, than that which was heated to
142°. The reason for this was not apparent. The
milk pasteurized at this plant was received from
the railroad in cans which had been shipped from
the country. The milk was dumped from these

219

THE PASTEURIZATION OF MILK

cans into a large dump vat, from which it was
pumped to a receiving vat upon the second floor
and was thence allowed to flow through a clarifier,
from which it was discharged into a large mixing
vat and thence flowed directly to the milk heater.

Firtu Trest.—This test was made at a plant at
which the milk was pasteurized by means of a
heater somewhat similar to that shown in Fig. 3.
The holder was like Fig. 21. In this heater the
milk is forced between two water-heated cylin-
ders, in one of which the water was at a tempera-
ture of 165°, and in the other of which the tem-
perature of the water was nearly at the boiling
point. The milk, while being heated, was kept in
agitation by means of a revolving arm, which was
so arranged that it moved between the two heat-
ing surfaces. The milk, after heating, was held
in a series of eight water-jacketed tanks, the water
surrounding the tanks being kept at a temperature
of from 145° to 150° F. The milk, while in this
holding tank, was kept in agitation by means of re-
volving metal stirrers.

A sample was first taken from one of the hold-
ing tanks in which the milk was heated to a tem-
perature of 143° F. and held there for thirty

220

FROM THE PRACTICAL VIEWPOINT |

minutes. This sample, when set, was found to
have 11 per cent. of cream in volume, and the but-
ter fat content was 3.7 per cent. A second sample
was taken from a holding tank in which milk had
been heated to a temperature of 147° and held
for thirty minutes, the temperature of the milk at
its discharge being 146°. This milk showed 4 per
cent. of cream and a fat content of 3.8 per cent.
A third sample was taken from a tank in which
milk was heated to 145° and held for thirty
minutes. This milk, when set, showed 7 per cent.
of cream and 3.7 per cent. butter fat. A fourth
sample was taken from milk which had been heated
to 146° and held for thirty minutes. This milk
showed 3 per cent. of cream and 3.9 per cent. but-
ter fat.

These results indicate that with this form of ap-
paratus the cream line was seriously interfered
with, even at a temperature as low as 143°. The
milk, as received in this plant, was poured from
cans into a receiving tank upon the upper floor
of the building from which it flowed to an appa-
ratus on the floor below in which it was preheated
to 60° F. It then passed through centrifugal
clarifiers from which it was discharged into a large

221

THE PASTEURIZATION OF MILK

tank upon the receiving floor. From this tank it
flowed by gravity to the pasteurizers on the floor
below.

Sixtu Trst.—This test was made at a plant in
which the milk was heated by means of an appa-
ratus shown in Fig. 11, where the milk is heated
by means of what is known as a Multitube Heater.
In this form of heater a series of large tubes are
so arranged that several smaller tubes extend
through them. The milk is forced through the
inner tubes, while hot water is forced through the
large surrounding tubes. After heating, the milk
is discharged into a series of eight holding tanks
similar to those described in test No. 5. The water
which is used to heat the milk in this apparatus is
itself heated in a tank outside of the milk heater
and is kept at a temperature varying between 144°
and 163°, the temperature rarely exceeding 154°.
From this tank the water is pumped to the milk-
heating apparatus.

The conditions at this plant were apparently fa-
vorable for securing good results. The fact that
the temperature of the heating water was carefully
controlled, made it impossible to superheat or
scorch any of the milk. The first sample of milk

222

FROM THE PRACTICAL VIEWPOINT

was taken from raw milk before it was clarified.
This sample, when set, showed 1314 per cent. of
cream and 3.4 per cent. butter fat. The second
sample was taken from one of the holding tanks
in which the milk was heated to a temperature of
146° and held thereafter for thirty minutes. This
sample, when set, showed no cream whatever on
the cream gauge, the fat being evidently evenly
distributed throughout the entire body of the milk.
This milk contained 3.5 per cent. of butter fat.
A third sample was taken from one of the holding
tanks in which the milk was heated to 143° F.
and held for thirty minutes. This milk showed,
upon standing, 10 per cent. of cream and 3.7 per
cent. butter fat. Sample No. 4 was taken from a
tank in which the milk was heated to 146° F. and
held for thirty minutes. This sample showed 5
per cent. of cream and 3.35 per cent. butter fat.

The results here obtained indicate that with this
apparatus if the milk was heated above 143° the
cream would be seriously affected.

Seventu Trst.—A test was made at still an-
other plant in which the milk was heated by means
of the pasteurizer shown in Fig. 9. In this appa-
ratus the milk is forced through a series of pipes

223

THE PASTEURIZATION OF MILK

which are enclosed in a large chamber which is
filled with hot water. The apparatus somewhat
resembles the tubular boiler. After heating, the
milk is held in three upright cylindrical Park hold-
ing tanks, the milk passing through the entire se-
ries. In this holding apparatus tests previously
made indicated that milk is held for from thirty-
five to forty minutes.

In making this test, the first sample was taken
from the raw milk. This sample, when set, showed
14 per cent. of cream and 3.8 per cent. butter fat.
A second sample was taken from milk which was
heated to a temperature of 143° and held for from
thirty-five to forty minutes. This sample, when
set, showed 14 per cent. of cream and 3.8 per cent.
butter fat. In order to vary the experiment the
temperature of the milk entering the holder was
then raised to 145°, at which temperature the milk
was maintained until the process of pasteurizing
was completed for the day. The milk in the filled
holding tanks was allowed to stand for thirty
minutes and a sample was taken from that which
was being discharged from the holding tank, which
showed, on standing, 14 per cent. of cream and
3.85 per cent. butter fat. A fourth sample was

224

FROM THE PRACTICAL VIEWPOINT

taken from the milk which was last discharged
from the holder. This milk had been in the holder
for exactly sixty minutes. Upon standing, this
milk showed 9 per cent. of cream and 3.7 per cent.
butter fat.

These results indicated that milk could be heated
to 145° and held for thirty minutes without any
injurious effect upon the cream line being pro-
duced, but that if the milk was held for an hour,
the cream line was considerably affected.

EientH Trst.—A further test was made at a
pasteurizing plant in which the milk was heated
by means of the heater shown in Fig. 7, and held
in the holder illustrated in Fig. 27. In this appa-
ratus the milk is forced through a series of pipes
which are themselves enclosed in a larger pipe
through which hot water is forced. The holding
apparatus consists of a series of large tubes
through which the milk is allowed to flow. It re-
quires about thirty-five minutes for the milk to be
discharged through the holding tubes.

A sample was taken from the raw milk, before
clarifying. This was found to contain 1514 per
cent. of cream and 3.5 per cent. butter fat. A sec-
ond sample was taken from milk which had been

225

THE PASTEURIZATION OF MILK

clarified, and this was found to contain 12 per cent.
cream and 3.6 per cent. butter fat, there being an
apparent reduction of 314 per cent. of cream vol-
ume due to the clarifying process. A third sam-
ple was taken from milk leaving the holder at a
temperature of 142°. This was found to contain
8 per cent. cream and 3.7 per cent. butter fat. A
fourth sample was taken from milk leaving the
holder at a temperature of 145°. This showed 7
per cent. of cream and 3.6 per cent. butter fat.

The results here obtained indicated that milk
which is heated to 145° shows about the same
amount of cream, by volume, as that which is
heated to 142°, but the milk heated to either tem-
perature showed but little more than half the
amount of cream which was found in the raw
milk,

The milk at this plant was received in the
dumping tank on the first floor, from which it was
pumped to a tank upon the pasteurizing floor, and
thence flowed through a centrifugal clarifier into
the mixing tank. From this tank it was pumped
through the heater and holder, and after being
discharged from the holder was again pumped
through the cooler.

226

FROM THE PRACTICAL VIEWPOINT |

Summary of Results

All the tests made indicate that when milk is
cleaned by a centrifugal clarifier, the volume of
cream in the milk suffers a reduction of 2 per cent.
to 3 per cent.

The number of tests made was probably not
sufficient to warrant the drawing of absolutely
definite conclusions. It was evident, however, that
the volume of cream in bottled milk was influenced
by various factors, some of which are apparently
little understood. These factors include:

(1) The temperature to which the milk is
heated.

(2) The length of time for which milk is held
at the high temperature.

(3) The temperature of the heating medium
with which the milk comes in contact during the
heating process.

(4) The clarification of the milk.

(5) The type of apparatus used in treating the
milk.

(6) The amount of agitation to which the milk
is subjected, especially while hot.

This last factor has a greater influence upon

227

THE PASTEURIZATION OF MILK

the cream line than is ordinarily appreciated. It
has been stated to the writer, that in one instance
where the cream line was materially reduced dur-
ing the pasteurization process, the experiment was
made of reducing the speed of the agitator which
kept the hot milk in motion. After the speed had
been so reduced it was found that the cream line
upon the milk resumed its normal character.

It will also be noted from the foregoing descrip-
tion of the various methods of handling milk that
in those plants where there was most agitation of
the milk, and especially where the pumping of
hot milk was practiced, the most difficulty with the
cream line was experienced. There are possibly
other factors which affect the cream line, among
which may be:

Ist, the age of the milk before pasteurization.

2nd, the grade of cows from which the milk was
produced.

8rd, the fact that milk has or has not been frozen
before being treated.

The tests made proved that it is entirely pos-
sible, under the most favorable conditions, to heat
milk to 145° and hold it for thirty minutes without
producing any injurious effect upon the cream line.

228

“

FROM THE PRACTICAL VIEWPOINT

It is also doubtless true, however, that with some
types of apparatus in use by the milk dealers and
with some conditions under which milk is handled,
a real difficulty is experienced in obtaining satis-
factory results.

The chart shown in Fig. 34, drawn by Dr. North,
indicates graphically the temperatures and holding
times within which it is safe to heat milk without
affecting the cream line. Such a chart cannot show
the other factors which also affect the results, such
as the amount of agitation, etc.

If the milk is being heated and an attempt is
made to keep the milk at a temperature no lower
than 145° F., it is almost certain that the tempera-
ture will at times reach from 146 to 148° or higher,
and that it will at times be held longer than thirty
minutes. It is almost mechanically impossible to
so control the temperature of milk while heating
that there will not be considerable variation.

The agitation probably has the effect of break-
ing up the fat globules into smaller masses. Since
each globule of fat is surrounded with a film of
casein or skim milk, which is heavier than the fat, it
is evident that as the mass of fat becomes smaller,
the proportional amount of the surrounding skim

229

THE PASTEURIZATION OF MILK

FAHRENHEIT

TEMPERAT URE

TIME AND TEMPERATURE FOR
176° MILK PASTEURIZATION.

ser)

C.F North, 1912.
10° 20 30° 40°
TIME IN MINUTES

Fic. 34

230

50 60

FROM THE PRACTICAL VIEWPOINT

ae

milk becomes greater, till we reach a point when
the buoyant fat cannot lift the heavier envelope,
and our balloon of fat stays down.

Just why the high heat and the long holding
seatters the fat permanently through the body of
the milk is not so clear. It may be due to chemical
changes which occur.

In the pasteurizing equipment described on
pages 124 and 131 it is claimed that the superheat-
ing of the held milk has a beneficial effect upon
the cream lines.

The tables following show graphically the re-
sults of the tests made. They indicate the varied
conditions under which milk was handled in the
various tests and the percentage of the cream upon
each sample as well as the percentage of butter fat
which was determined by the Babcock test.

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239

CONCLUSION

In conclusion, it may not be amiss to say that all
the indications lead to the conviction that the pas-
teurization of milk is not, as some have claimed, a
fad. It is coming more and more into use, as a
recognized sanitary measure, which is at present
necessary. Whether a time may come when it will
be safe for large communities to consume their
milk unheated is a question which at present is not
a subject for practical consideration. The South
and West, which have been slow to recognize the
value of pasteurization, are coming into line, and
the teaching of practical methods of handling ap-
paratus used in pasteurizing milk is a wise thing
for the dairy schools to take up. Practical meth-
ods of controlling the actual operation of pasteuriz-
ing plants should be taught, and instruction should
be available for inspectors employed by munici-
palities, as well as for those who are to become
such inspectors, in order that they may be equipped
to render the most useful service to the com-
munities when they assume their duties.

240

THE PASTEURIZATION OF: MILK:
Le a Eee RE SEES ARES: eR

Other methods may be discovered by which milk
may be rendered safe with less trouble and ex-
pense, but none such are now in sight, and until
they appear our towns and cities must depend upon
the proper application of heat to render milk safe
as food.

It is due to the citizens that the actual treatment
of the milk be so intelligently supervised and con-
trolled that it will in reality be as safe as the
people have a right to expect.

241

INDEX

A
PAGE
Puiteration of Milk ...:66 6605s es eee 5, 6
mericutural Department... 2... :i +3): 2
imteet. 5.5 oe. net at Fee sieges cals 11
Rae MMA DECSSORS: 6. ws sw ois ka eee 135
myers and Johnson) ..... 256.22. «- 9, 86,155
B
Heards of Food Control’... .. 02032. ses 2
PERE OCRIDINE ot. 8 os SUS e ls Paw A 8 177-180
Pee PEARIO Oo. 8 Koss eddies alee 163-175
a IUNI ns is Guy sporti Mp Flew Was 176
Ree CAGED ue 5 a ace ee eg eves arate ee 180-182
eve 1 whereniosis: 6. SS See 18-22
C
POMREMIREE ESGEEIOS. 6S Sw gL vise ee ee te oe 177-180
eiemeeal: Chants. 5. se Ss wn ee 27
Cleaning and Clarifying .............- 150-155
RE oS ey eS Rha Atala ela ial 115,116
eememtOED AIR cise choo nls, knee Ries 135
PERE 5.5 Sion 5d se WOR ay Cac ae 240

INDEX

PAGE

Containers, Washing of ...'..... <./..5 208 163-175

Control (Official) of Pasteurization..... 32-34

Controllers, Temperature .......... 27, 133-140

Cooling... 4 45 SAS ee a 155

Coolers, “Open: 05:66) ics Pos PORE 155-160

Vande) 202 idee ssp cee be ee .. 160-161

Tubolarc3 i654 6$i 03 at ose 162

Cream Tambo.) On. eee ae 21, 29, 208-239
D

Department of Health, Reprints........ 9

Mow Work City 2460s iah ean 27, 43, 94, 209

Piet 66505 3 ees oho 2 11,
E

Efficiency of Apparatus .........¢sn06en 185-207

Electric. Process sbi cac So 2 eee 90, 91

EGayUles ©. ooo cn sa eee 3 Peete 30
F

Filling Bottles .). .oee 3240500 176

PESOS iy s oss Te SO ee Ce ee 11
G

Geneva Experiment Station ........... . 19,1758

244

INDEX

H
PAGE
@emita Department... oc. ok oc 2
Brew York City .......4. 9, 27, 43, 94, 209
Se Soret soon ing hc a cleeole eee 43
Re PME ei. oy eS Fe Bess ee - 44-47
eee PHC Sy sc oa eee 47-56
Ee ie Sale 15. Se oe 56-65
MRR AES EHD oe id ane ava: Sea we 65-77
Pan Dye. cca ei. Ce A 77-89
Holding Time, Method of Calculation... 96, 103
So IIR See ee Mage) = oe 94-107
EMP LONG 3. be ls oe ee 94-111
Points to be Observed in....... 108, 109
Continuous or Flow Type.......... LlI-—132
Disturbances of Holding Time. .113, 114
Itemaonial ‘Tank «60... pawns 124-126
Be AR AS oa a aig Ew ee 111-123
Testing of Holding Time...... 115, 116
ERS 0 5 ep Ble Grete 126-129
Pema s aBbeurination .......266.66.cae. 183, 184
I
Remmeemenare Of Wilk os ae wy 4, 5, 18-22

| PAGE

JaCODE 0 EVEN Se? Meee ee eee 13

Johnson 9s 2226 O54 3a eee 9, 86, 158
K

Kulp. os. cscs dhe ees cass ay, be 158
M

Milk Dealers’ Organizations ........... 6,7

Milk, Changes Due to Pasteurization.... a7

Methods of Official Control............ 32-34
N

New York City ..... 9, 15, 27, 43, 94, 209, 258
O

Ozone Treatment: :. 6.601} . 4 cee 92
P

Parke oe 20, 23, 111

Pasteur’. 605i ose Ca Oa 10

Paper Bottles... 60056 66.0 0 eeeeee 180-182

INDEX

PAGE
Pusteurization in General ............. 1-42
Pasteurization Literature ............. 9
pestcarizgation, Home . .... 2th Sess 6 183, 184

DN THORE ooo bea Mies oe oe 27
Pasteurized Milk, Requirements for Secur-

me Gond. Resilte: 22. 16s. cen $1,. 32
Meermtiser. Danish ....:425..). .ao0 8 = wens Lt. F2
Pasteurizing Plant, Requirements for Sat-

istactory Equipment... ,..... 5...) 36-42
Pasteurizing in Vacuum Pans .......... 89, 90
Percentage of Bacterial Reduction....... 185-207
Publis, Health Reports 2.6.0... 0... ds 18
De ee be be a ev oy ee 39

R
Hecorders—Temperature ..........-. 4: 140-149
aia aia kg x same u 8-8 Sw nen kw 11
a ee aa eee 9. 29, 23; 25, 183
Meme MAH UG) oe ON ee tle Casein ole 158
S

I a8 nk eRe ow no ate jana wr ecakee pa |
Pepimare “Throat... sos isaccie ese ee dm 6 17,18
as Br es a a Gus Sa enn es 10

INDEX

PAGE

Sohxlet . 06 os axe as soe eee 13

Storch : Test. (si... 635 oe 32

Superheating of Milk .........ii%.)) eh 131
i

Temperature ‘Controller .. 0.2.22 2 27, 133-140

Temperature Test, Holding Tanks..... 115, 116

Temperature Recordefs'. +). :... 29a 140-149

Testing Cleaned Containers ........... 174, 175

Testing of Holding Time |. .'°:). S323 115, 116

Thermal:Death Point). 22)... se 27

Taberculosis: 2. 0450 ea cen ee Re 12, 18-21

Pyphoid | Fever: .,.. 002.2 toe ee 17
U

Ultra, Violet Rays >... . 650 53.05 cGy 92
V

Vaeuum Pans (2... 2.08%... <5 3 a eee 89, 90
W

Washing of Containers ............+: 163-175

Winslow +... 065 oe ed Se 18.

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