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BULLETIN No. 342

Washington, D. C. Issued January 8, 1916; revised October 10, 1922

THE PRESENT STATUS OF THE "ASTAURIZATION.
OF MILK. i ‘ ; > & V
399

By S. Henry AYERS, te} NO Va i¥2Z
Bacteriologist, Dairy Division, Bureau of, Aqinal Jydustw.« aghoultere

errr ey eer Se Lk

CONTENTS.
Page. Page
Meaning of the term pasteurization_ 1 | Handling milk after pasteurization_ 15
Valse of Pasreuriza tion <— | -_-_ 2 | Cost of pasteurizing milk. 2. 16
Electrical and ultra-violet-ray treat- Bacteria which survive pasteuriza-
OVE Tc RCO) 1k ee ee ee 4 OW Sod Fen Aes Gee ge SGA OS 16
Extent of pasteurization in the The colon test for efficiency of pas-
Limnbed Esietlesee et Se ee SS TT ye Hi) teurizalion 22722 <3 Sey. See 20
Methods of pasteurization________~- 7 | Past and present theories of aataae
Advantages of low-temperature pas- PZE OI OG a es ee 20
‘Males hintyi es ree eee eee eee a 10 | Pasteurization and vitamins_______ 22
Temperatures and methods most suit- The necessity for pasteurigation____ 24
able for pasteurization__________ aft | References to literature___________ 25
Supervision of the process___-______ 13

MEANING OF THE TERM PASTEURIZATION.

The term “pasteurization” originated from the experiments of
Louis Pasteur, in France. From 1860 to 1864, in experiments on the
“diseases” of wine, he found that heating for a few moments at
temperatures of from 122° to 140° F. was sufficient to prevent abnor-
mal fermentations and souring in wine. A little later he found
that by a similar heating beer could be preserved from souring.
The applicaticn of the process gave rise to the term “ pasteurization.”
As applied under commercial conditions, pasteurization is the process
of heating for a short or a long period, as the different processes
demand, at temperatures usually between 140° and 185° F. As ap-
plied: to milk for direct consumption, pasteurization should mean
a process of heating to 145° F. and holding at that temperature for
30 minutes. The process is followed by rapid cooling.

Jt is believed that the term pasteurization should be applied only
to. the process of heating at 145° F’. for a period of 30 minutes.

107148°—22—__1

Z BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.
VALUE OF PASTEURIZATION.

From a sanitary standpoint, the value of pasteurization is of
greatest importance when market milk is under consideration. The
pasteurization of milk, when the process is properly performed,
affords protection from pathogenic organisms. Such disease-pro-
ducing bacteria as Bacillus tuberculosis, B. diphtherie, B. typhi,
and other organisms of the typhoid-paratyphoid group, and the
dysentery bacillus, when heated at 140° F. for 20 minutes or more
are destroyed, or at least lose their ability to produce disease.

Occasionally results are reported, such as those of Twiss (30),2
which again open the question as to the destruction of certain patho-
genic organisms by pasteurization. Using test organisms of the
typhoid-paratyphoid group, she obtained results which indicated
that there was not a complete destruction of these organisms when
heated in milk at 140° F. and even at 149° F. for 30 minutes. Krum-
wiede and Noble (24), however, using some of the same test organ-
isms of the typhoid-paratyphoid group as used by Twiss, found that
_ they did not survive heating for 10 minutes at 140° F. They further
pointed out that the apparent heat resistance of the strains used by
Twiss was due to the method of determining their thermal death

point.

_ According to Mohler (25), pasteurization offers protection against
foot-and-mouth disease. He makes the following statement:

Milk which has been pasteurized for the elimination of tubercle and typhoid
bacilli will not prove capable of transmitting the disease (foot-and-mouth) to
persons or animals fed with it.

In view of the outbreak of foot-and-mouth disease in this country
a few years ago this statement is of importance.

The abortuslike bacteria in the udders of healthy cows which were
demonstrated by Evans (15) may also be considered in a discussion
of pasteurization. Although their sanitary significance has not been
definitely established, it is interesting to observe that it was found
by Evans (16) that both the pathogenic and lipolytic varieties could
be destroyed by heating to 125° F. for 30 minutes or to 145° F. for
30 seconds.

Within recent years several epidemics of septic sore throat have
been traced to milk. In some of these epidemics it was found
possible, by pasteurization, to destroy streptococci which were iso-
lated from throats of infected people and which were believed to
be the infective agents. Pasteurization, properly performed, seems
to protect against epidemics of this kind, but until the organism

1See References to literature.

ce ee

eee oe eee es ae Pee

STATUS OF PASTEURIZATION OF MILK. 3

which causes the disease is definitely known it is impossible to say
that it affords absolute protection.

Since it is quite generally believed that the streptococci are the
causative agents of septic sore throat, the ability of certain of this
group of organisms to stand temperatures above that of pasteuriza-
tion naturally presents a grave situation. If pathogenic streptococci
are able to survive the usual process of pasteurization, the value of
the process, from a sanitary standpoint, is materially lowered.

Experience with the use of properly pasteurized milk and the de-
termination of the thermal death point of pathogenic streptococci
by various investigators indicate very clearly, however, that the
thermal death point of these organisms is relatively low and that
they are readily destroyed by proper pasteurization. Thus Ham-
burger (17), who studied the epidemic of septic sore throat in
Baltimore in 1912, traced this epidemic to a certain milk supply.
Advice was given to boil all milk, and the dairy connected with
the epidemic raised the temperature of its flash pasteurization to
160° F.; then it changed to the holder process by which the mill
was heated to 145° F. and held for a period of 30 minutes. The
cases of sore throat that followed were neither so severe nor so
numerous and did not follow the milk supply, but appeared to
have been transmitted from individual to individual. Hamburger
(18) also found that a streptococcus isolated from a patient having
a case of sore throat was killed by heating in milk at 145° F. for
30 minutes.

Again, Capps and Miller (12) who studied the Chicago epi-
demic of septic sore throat, traced it to a dairy where the milk was
pasteurized by the flash process at 160° F. On certain dates they
found that there was a pronounced failure to pasteurize and follow-
ing these dates there were outbreaks of septic sore throat. These
authors believed that the final responsibility for the epidemic rested
on the inadequate and unreliable pasteurization. They state that
the absolute protection of the children of the Michael Reese Hos-
pital from infection by efficient pasteurization demonstrates this
point. Bray (11), who studied an epidemic of tonsillitis of tuber-
culous patients, traced the epidemic to a milk supply of one farm
where a carrier presumably infected the milk. Forty cases of
tonsillitis resulted among 400 people. As soon as the epidemic
broke out the milk was pasteurized, and from that time only 1
case appeared.

From the results achieved from the proper pasteurization of milk
it seems evident that the thermal death point of pathogenic strep-
tococci, which cause septic sore throat, is relatively low. This belief

4 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.

is borne out by the results of the studies of Davis (13), who found
that streptococci isolated from cases of sore throat were readily killed
by heating at 140° F. for 30 minutes. He also found that none of 24
strains of pathogenic hemolytic streptococci of human origin resisted
heating at 140° F. for 30 minutes. He makes the following statement:

I know of no evidence that strains of streptococci pathogenic to man can resist
the usual temperature of pasteurization, 145° F., for 30 minutes.

Further evidence that pathogenic streptococci are destroyed by
proper pasteurization was presented by the results obtained by Ayers,
Johnson, and Davis (7), who found that 27 strains of these organisms
were always destroyed by heating at 140° F. for 30 minutes.

Epidemics of scarlet fever have been traced to milk supplies, and
in such cases pasteurization has been resorted to, with apparently
satisfactory results, as a means of safeguarding the public health.

Pasteurization is of value from a commercial standpoint so far as
it increases the keeping quality of the milk and assists in preventing
financial losses by souring. As practiced at the present time, commer-
cial pasteurization, with reasonable care, destroys about 99 per cent
of the bacteria (this percentage varies, depending upon the propor-
tion of heat-resistant bacteria in the milk), and while it does not
prevent the ultimate souring of milk, it does delay the process. At
the present time pasteurization is the best process for the destruction
of bacteria in milk on a commercial scale.

ELECTRICAL AND ULTRA-VIOLET-RAY TREATMENT OF MILK.

Many attempts have been made to destroy bacteria in milk by
means of electricity, but no process has been devised which has been
commercially applied to any great extent.

Alternating currents have been most extensively worked with, be-
cause direct currents were found to produce undesirable chemical
changesin milk. While the proper application of suitable alternating
currents has resulted in bacteria reductions similar to those produced
by pasteurization, it appears to be an open question as to whether
the action of the electric current is due to the heat generated or to
the direct action of electricity on the bacterial cells. |

Thornton (28), who studied this question in England, came to the
conclusion that the destruction of bacteria must be regarded as due
largely to thermal changes rather than electrical, but thought his
results indicated some electrical action on the molecular structure of
the bacteria. Beattie (8, 9), also working in England on the same
problem, came to the conclusion that heat was not the principal fac-
tor in the destruction of bacteria by electricity, but found that to
obtain satisfactory results the temperature should not be below 145°

‘
3
-*
¥

STATUS OF PASTEURIZATION OF MILK. 5

F. In the United States an electric process has been investigated by
Anderson and Finkelstein (1). Their conclusion as to the cause of
the destruction of the bacteria is as follows:

The destruction of bacteria in the “ ” process is apparently due to
the heat produced. by the electric current rather than to the electric current
itself. The ‘“ ” process furnishes a method for producing a very
sudden high temperature for a brief period of time.

It seems evident from a review of the literature that in the use of
electricity, as it has been applied, sufficient heat is generated by elec-
tricity, or a combination of steam and electricity, to raise the milk
to the pasteurizing temperature.. Since the temperatures reached
are in themselves destructive to most nonspore-forming bacteria,
the problem of determining whether the effect of electricity is due
to heat or direct electric action is a difficult one.

The use of ultra-violet rays for the destruction of bacteria in milk
has not proved to be of value as a commercial process. Experiments
with these rays carried on by Ayers and Johnston (5) showed that
while the rays cause great destruction of bacteria in milk, when ex-
posed under suitable conditions, the process in its present state of
development can not replace that of pasteurization on a commercial
scale. It is difficult to obtain the proper exposure of milk to the
rays on a scale sufficient to permit of practical operation and im-
practicable to secure suitable bacteria reductions without seriously
injuring the flavor of the milk.

EXTENT OF PASTEURIZATION IN THE UNITED STATES.

Pasteurization when first practiced by milk dealers in this country
was carried on more or less secretly, and, except as a means of pre-

serving the milk, was regarded by them as a process of no value. As

the practice became more general the subject of pasteurization was
studied, and its value as a means of destroying disease-producing
bacteria was recognized. In consequence of the recognition of the
merits of the process there has been during the last 20 years a rapid
increase in the quantity of milk pasteurized. Jordan (23), in a paper
published in 1913, stated that 10 years previously only about 5 per
cent of the milk supply of New York City was pasteurized; figures
from other sources show that about 40 per cent in 1912, 88 per cent
in 1914, and 98 per cent in 1921 was pasteurized. In Boston very
little milk was pasteurized in 1902, but in 1915 80 per cent, while at
present about 90 per cent is so treated. In many of the smaller cities
there have been corresponding increases in the quantity of milk
pasteurized during the last few years.

The general tendency in this country to-day is toward the pasteuri-
zation of all milk for direct consumption, with the exception of

6 BULLETIN 32, U. S. DEPARTMENT OF AGRICULTURE.

certified or equivalent grades of milk from tuberculin-tested herds.
Some idea of the increase in the extent of pasteurization in the United
States from 1915 to 1921 may be gained by a study of Table 1. The
figures were obtained from a questionnaire sent to health officers. In
1915 the figures were based on 344 replies and 379 in 1921.

TABLE 1.—Eztent of pasteurization of milk in cities m the United States of
more than 10,000 population in 1915 and 1921.

10,001 to 25,000... ... 168 126

It will be noted that since 1915 there has been a great increase in
the percentage of cities in which more than 50 per cent of the milk
is pasteurized. There has been during the same period a marked
decrease in the percentage of cities having no pasteurized milk.

Table 1 does not contain any data from cities of less than 10,000
population, but replies from 88 such cities showed the following
figures: In 22 cities 50 per cent or more of the milk was pasteurized,
in 12 others from 11 to 50 per cent, and in two cities 10 per cent
or less was so treated. Fifty-two of the 88 cities reported no pas-
teurized milk. It seems evident, therefore, that the process of pas-
teurization is being used extensively in this country even in the
small cities.

A study of the available figures on the extent of pasteurization
revealed a few more facts which may be of interest. Im 1915 milk
was pasteurized in about 62 per cent of the cities with a population
above 10,000, and in 1921 in about 80 per cent of such cities. The
increase in pasteurization in small cities, 10,000 to 25,000, is shown
hy the fact that in 1915 about 40 per cent of these cities reported
pasteurized milk compared with approximately 61 per cent in 1921.

Considering these figures as a whole the increasing trend of pas-
teurization is plain.

A good idea of the present extent of pasteurization may be
obtained from Table 2. It will be observed that there is an increas-
ing tendency, which follows their increasing population, for cities
to have pasteurized milk and also to pasteurize a higher percentage
of the supply.

ee a Se ae Se ee ee a, en

STATUS OF PASTEURIZATION OF MILK. 7

TABLE 2.—Proportion of cities having pasteurized milk and average per cent of
their milk supply which was pasteurized in 1921.

Number of | Number of} Percent Average

cities cities of cities per cent
Population of cities. reporting with no with of milk
pasteur- pasteur- pasteur- pasteur-

ized milk. | ized milk. | ized milk. ized.

Morena 500: (00> 24 5 58 oe See, 12 0 100 95
TO OOIT ODO 000M thet aoe an See a eae Ea ruy ay. ts 42 0 100 72
OO COD OOOEE. ees sas >. oc. me, Rep tien BE Oh 15 0 100 68
SOOT O75 UO eee as. oe ee a ea ee Id Sereda ee 2 29 5 85 65
ENE SONG PR a2 So Oo ko sate et tes ts Se 55 7 89 58
MOROCCAN 2 doo cae sae Seth Ose cee oe ab ae 77 49 61 51
LU ESSU ICING 1 Gees See ie eee ee = Fan eet AER yS 36 52 41 53

PAN [ro bees tee aie ees oe I. eee a Re 266 Psu ls Sse Sela oe ee

For those who are particularly interested in the quantity of milk
pasteurized in various cities, Table 3 has been prepared. In it is a
list of 266 cities that reported pasteurized milk and the approxi-
mate quantity of milk pasteurized. The cities are listed in order of
their population given in the 1920 census and include all cities re-
porting pasteurization up to the time the table was prepared. It is
particularly interesting to note the extent to which milk is
pasteurized even in the smal] cities.

METHODS OF PASTEURIZATION.

At present three processes of pasteurization are practiced in this
country. The first is known as the flash, or continuous process; the
second, the holder, or holding process; and the third is known as
pasteurization in the bottle.

TABLE 3.—Approximate quantity of milk pasteurized in various cities as shown
by returns from questionnaire sent in 1921.

Per cent Per cent
Popula- A Popula- :
City. tion, 1920] Of milk City. tion, 1920] Of mile

census. | toutrized. census: | terized.

Wow: York, No Ye foo 85-35. 5, 620, 048 98:\)- Columbus: Onion 4-222. <-5.5: 237, 031 75
lereten Wile e 2,701, 705 98 fl Mouisville: Ky 2. to eS) 234, 891 85
Philadelphia, Pa............- 1, 823, 799 O8iIl St.Paul, Minn i... 92252205: 934, 595 60
Depot, Mich--s_-....-.-..... 993, 678 Osi Micron. OHIO te oie sso 208, 435 98
Cicyeland, Ohio... .-...:...:- 796, 841 BS he Omaha Nebe <2. sett stt es 191, 601 30
DOW S PMO x sao soo osa es 772, 892 92 || Worcester, Mass...........-.-- 179, 754 65
aston, Massoeses 028222252. 748, 060 OO | WO VEACUSC NERY one eee eee ee AAT 66
Ralamoere Md se. 2 222i 25... l | 733, 826 OS RACH mMonG: Vase sen ose 171, 667 97
1B HiG OL EU 3 ees a | 588, 343 95 || New Haven, Conn...........- 162, 537 55
Los Angeles, Calif..........-. 576, 673 86) ||) Memphis;“Tenn== === =222222- 162, 351 50
S52 a 506, 775 100 || Dallas, Tex......-.--.----.--- 158, 976 70
San Francisco, Calif. ......... 506, 676 Shi Dayton. Ohio eas.) 2) saee" 152, 559 95
Milwaukee, Wis.........---.-- 457, 147 98:1 ouston) Text tee. 25.462 53s: 138, 296 50
Washington, "DiC 2. $225..22.- 437, 571 9is|\HartiordlConne-sssscee. 2 see 138, 036 70
GWA KEIN Uma -\scit 2s cess 414, 524 80 || Grand Hapics, Miches= esse: 137, 634 90
Cinemnati, Ohio-2: 5. 2.222... 401, 247 983 ||\patersony NERO... oe secon. © 135, 875 80
Minneapolis, Minn...........- 380, 582 94 || Youngstown, Ohio. ........-- 132, 358 92
Kansas City; Mo......-.-.---. 324, 410 50 || Springfield, Mass......-....-. 129, 614 95
meabhle»Wastt! 22.2 .222222552. 315, 312 85 || New Bedford, Mass.........-- 121, 217 40
eechestersinery 20s. 5.5.2.522- 295, 750 Gol walPRiveriMasss: = pee cee 120, 485 55
Rartlands Oreg.)...$2.5.2-252 258, 288 Hau erentonewNe dee cemecasoe sees 119, 289 60
BenvercCole. . oS. 562222522 256, 491 80 || Nashville, Tenn............-- 118, 342 40

Providence, R.I.........---. 237, 595 60 || Salt Lake City, Utah.......-- 118, 110 88

8 _ BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.

TABLE 3.—Approximate quantity of milk pasteurized in various cities as shown
by returns from questionnaire sent in 1921—Continued.

Popula- | Fer cent |

op i Popula- Per cent
City. tion, 1920) Of milk | City. tion, 1920| of milk
census. | ;ourized. || census. ino esa
MorialkowV ak aeock icc chs kc 115,777 50 || San Jose, Calif... .2252-5.22 39, 642 70
mulpary IN. I¥ias2 ss. scones - 113, 344 60 || Dubuque, Iowa... -....222... 39, 141 50
Eowell, Massc. 20 - c AS.. 112, 759 34 || Brookline, Mass..-........... 37, 748 88
“The Oranges” TaN Jeo eee 111, 958 91 || (Golambia, SaGs ees or aie 37, 524 15
Wilmington, Del........-.--- 110, 168 66°, d,oram, OIG... .2ss5soeeees 37, 295 99
aReniti re Pt 5405. 2S: a Rep 107, 784 96 || Evanston, Ml................. 37, 234 99.5
Kansas City, Kans. .....---.- 101, 177 65 |! Waterloo, lowa...........__.. 36, 230 90
Wanker oN. Yo 365.6) 100, 176 98 || Williamsport, Pa............. 36, 198 75
dgyiin, Mass) 2% 502k. .) ere 99, 148 19.1 Agiborn: Ne Yoss5 5-2 36, 192 15
DBalush Mann, 5 Seek ee | 98,917 46 || Newport News, Va..........- 35, 596 50
Piizabeth Ned ose hseen es | 95, 283 87 || Poughkeepsie, N. Y.-.....__. 35, 000 95
b OTe Peictc 0 Van yg ee a UE 93, 372 10'|| feriden. Conus .-< 22 ee 34, 764 10
Somerville, Mass............. 93, 091 85 || Pontiac, Mich.-_......... 34, 273 50
Pink, Mick. § 2 CET SS 91, 599 80 ll Maston, Pass, 25.2) aoe ee 73
Jacksonville, Fla...........-- | 91, 558 (01 Ochkoshowiss, Sota 33, 162 25 ?
Oklahoma, Okla sissies) =)=im late niet =i = 91, 295 75 Ogden Utah ts A hase ee 32, 804 50 ‘
Schenectady, N. Y....-..-.-- | 88, 723 36 |! Green Bay, Wis..--......-- 31, 017 75 :
Clintons Ohio. 254.._TF | 87,091 30" Negnort fu | ee) peers 90
Evansville, Ind..............- | 85,264 80 |i Goloado Springs, Col "| 30,105 85 |
a= Colorado Springs, Colo........ , '
Honolulu, Hawaii..........-. | 83,327 451! 7 vnchbure, Va 30, 070 40 4
Manchester, N. H............| 78,384 CDN rae eee ag peyiO wal 29, 053 25
Se sosephy, Mo..220 ee ess: | 77, 939 Us ear rie arr i a Pano Po 28, 806 90
LDU ESTA bs Caan a ae 77, 560 33. lines ap VN Ce GE ee 28, 379 40 :
Allentown, Pa..........-..... | 73,502 (bg We enene Ais Se nena so 28, 064 20
South Bend, Ind............. | 70, 983 90 | rar cticld ¢ Glib batt ee 27, 824 80 |
Portland, Me.............---- | 69,272 8 On RE. Nos ee a 27, 700 75 .
@harleston’ 8) @2co, oy | 67,957 100 cna cote) With ich at as 27) 644 75
Jennstowsaiy Pas. ce. oo 222305 | 67,327 50 ayia RE Wee aa ee 26, 341 10
Binghamton, N. Y..........- | 66, 800 75 ae Nig ee eee 26, 224 80
Rueictord Wie 2. cel. | 65,651 92 | Grae Walk Eee 25, 202 50
Little Rock, Ark............. | 65, 142 BO Se ee ee ee 24 057 30
Saginaw, Mich................ | 61, 903 41 || x eee Ohio: ee 23” 504 98
Springfield, Ohio............. 60, 840 Uy cece Uae eres coer 23,197 33
Altoona, Pal 0201200. | 60,331 OF iG TPEn VEO erasa State 22, 307 100
Holyoke, Mass.....-.......:-. | 60, 203 75 SanGusly, Wibal asc (geo i 22,779 30
New Britain,Conn....__....| 59, 316 207 1B aN iO Meee" esas 22) 561 45
Springfield, M1.....22222222277 | 59,183 04 || CHEN Ena a ee 22) 486 90
Waring, Wis... --<1.-..31.1...| 58, 593 B5 | Ee Seer eee 21, 961 50
Chattanooga, Tenn........... 57, 895 80 || Fargo, AN iGo 21,719 15
Hrarsing, Mich. oo... 50.0) oe. 57, 327 0) ope Did See 21, 626 50
Gary tad ek ag Fick: 56, 378 100; || ROGuCs Es aes ene 21, 393 7
‘Wheeling, W. Va.............| 56, 208 15 ee eee as aa 21, 284 80
Berkeley, Calif... .....2..2:2. | 56, 036 82 Below : o Wis ee Swe 20, 906 65
Long Beach, Calif... -.-...1..) 55,593 80 eae ee pant Mao 20, 879 100
Hincolm, Nevres ec ee | 54,948 70 ae ee: ibs > 90) 474 85
Haverhill, Mass.............- 53, 844 25 | yes 20, 299 50
MiawiCasier ea. toes nto | 93, 150 50 SE say Se Ee a 20, 065 50
a TAVIS Fo Cf he Ce eee | 52,548 20 || Mason. ©ivy, nN. Oe 2 ae 19, 861 8
Teaipa tinge 1 6320, | 51,252 ee eA ied ay ae ia 19,653 | 100
Rognoke, Vaulo2i. 50, 842 Re SE Saenger 19, 516 75
Niagara. PalisvN? ¥ J. . 2222252 | 50, 670 95 || Ann Sent Sait cores eeee- 19° 44] 20
Tppeks, Hans secs 50, 022 £0. eS ee 19, 336 15
Winston-Salem, N.C......-.. ' 48,395 50 || Dunkirk, N.Y -------------.- 19. 143 70
Jackson, Mich................ | 48,374 30, || Winona, MUN. 9955-222 2< 2 ae 18, 661 25
Quincy, Mass.......2....-.... | 47,876 Bil Wiousaay Wie ae Les sae 18, 539 80
Cedar Rapids, Iowa......--.- 45, 566 75 || Yakima, | vv Fa a ERT ee 18, 060 8
PimiracN) Ves sce ete | 45,393 33 ae cae Tat Tae 17. 734 90 ,
ivcro Ne eek ee 44, 955 75 || Anniston, Ala. . fi doesneekes 17. 677 100 '
Mow Castile: Bay a ee. tee | 44, 938 45 Hackensack, BS a2 ae ee aes 17. 033 50 :
Presn Os (C alidee sees Sates oe See | 44,616 40 Framingham, BIAS ---< ~~ 17. 004 25 P
isnlveston tex eee bet Ors 44,255 15 || Ithaca, N. ¥..-----------2--- 16. 971 20
Montgomery, Ala.........--.. 43, 464 50 || Gardner, eter 5A eee ero 16. 843 99 :
gE FCN) Pojed 71) Ce aia ak lng ping ee | 43,050 55 || Richmond, Calif-...-......... 15, 820 12 3
Wit. Vernon. aNcoy eos... csc ce | 42,726 100 || Corning, N. Y .-..--.--------- 15, 873 100 ‘
Bdlprat) Masso ot Wek St. | 42,515 60 || Champaign, Ill --...-..-....- 15, 868 10 ~<
Perth Amboy, N.J........... | 41,707 85 || Peekskill, N. Y.-....--.---..- 15, 831 55 '
Bite; Molise sss2 see eee. 41,611 33 || Chillicothe, Ohio. aa pores: = 15. 731 10 '
Lexington, Ky ee a ee 41, 534 35 Marshalltow n, Iowa SS 15. 482 80 §
Pittsfield, Macca =o SRI 41, 534 14 North Tonawanda, N.Y...-.- 15, 462 20
Lima, Ohio ESS OY eS 41, 326 j 50 | Greenfield, Mass Se ae, oe ae 15. 195 95 ~.
Fitchburg, Mass.........----- 41,013 13 || Mishawaka, Ind...-...------- 15, 157 40 ;
Kenosha, j YT shied I is SR ae Sete eeaoiee 40, 472 75 Albuquerque, N. Mex....---- F 100 16 ]
Biockteon satis: cack o32tia 2: 40, 296 90 || Billings, Mont..........------ ” A 50 |
BVOLetL, MASSeuyess fuse cee 40, 120 98 || Piqua, Ohio ek gate oe Sa ee 4 eis 84 '
Wichita Falls, Tex..........- 40, 079 20 || treneva, Ni Ws 34 Se. = y= = 5 a 50
Hamilton, Ohio........-..--- 39, 675 100 || Tiffin, Ohio. Setar wt S SASS SRS a 10
PELIOly WAN aes. ccsem ete ot 39, 671 60 || Bridgeton, N. J............... 14, 323
“The Oranges’? include Orange, East Orange and West Orange, South Orange village, and South ;
Orange township. |
fay
3

STATUS OF PASTEURIZATION OF MILK. 9

TABLE 3.—Approximate quantity of milk pasteurized in various cities as shown
by returns from questionnaire sent in 1921—Continued.

| |
Per cent || | Per cent
Popula- : | Popula- | :
City. tion, 1920 Bare | City. tion, 1920) ue sigs
Census. | teurized. || aDSHS Micnriced:
> Coe PT Pie | Ges Fe neva a ee OP
FUGhPoint.wN. Cp. sg0.t ce. 14, 302 20; || Ashland + ORO x 45.26 so. 9, 249 70
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Bvochester; Minn>..-° 22 =sd2. 13, 722 Soi, Bedtord 5 nd. <2 /s45. = =552542- 9, 076 60
WMonewpranchs Ned's 2 2sss 0. 13, 521 79 ||-Welisville, Ohio... .... 22. --- 8, 849 50
NWatervillo Me... 5.28 oot 4 13, 351 5 || Washington, Ind............. 8, 743 50
COLMAN NG se ee se cock sono 13, 294 1OF||PELanOVeR ha nese sees cen eee 8, 664 30
sab rekag Calif geo. 3s eysk 13, 212 65 |} Mitehell, |S. Daks-.2.2.2.-2%.- 8,478 40
DHEAUO PA NY eee ee ore oe 13, 181 35 |} Manhattan, Kans............. 7, 989 23
Cambridge, Ohio. ............ 13, 104 50 ||.,Die- Kalb, dl. one se sect ae 2 7, 871 75
Marquette, Mich.............. 12’ 718 30 |\sSuleii Ne gates ss ene 7, 435 25
Morristown, N. Jo. .....2:.-.-| ~ 12,548 25 || Marblehead, Mass............ 7, 348 80
Mawrence. Kans*s. 2-2-2924 12, 456 4 CVINIOUT NG se Seen 7, 348 75
GONE sWOwacwe cot cca ee. aoe 12,451 10.}| Niles “Mich. 444-08) $5 <* Sil 75
Asbury bank, "Ne J- == 5.2.2 2s: 12, 400 95 || Painesville, Ohio............. Mahe 56
Benton Harbor, Mich........- 12, 227 @57) | Merincetons Inde ashen eee 7, 132 25
Tuscaloosa, Ala-..-........... 11, 996 75 || Bemidji, Minn............... 7; 096 25
Independence, Kans.......... 11, 920 Geli av Oswell, Ni... Mexans8. 085 2. 7, 062 25
Martins Ferry, Ohio.......... 11, 634 80 || Rumford Falls, Me........... 7, 016 30
ran ktoris ind eee = 11, 585 66: eNewarkeuN Yeo Soe eee oe 6, 964 85
Fairfield, Conn........ Benes 11, 475 Seti eANleyOr OP UU ieee see he Ce 6, 757 50
Arkansas City, Kans ........- 11, 253 “Gy I ARS ROL WESe seesc oe soso se oe ae | 6, 729 10
_ Florence, S.C. 21. 2.222 22.2... 10, 968 17°]! Medina: Na Youre i AV os irs | 6, 011 50
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Plwood; md=.2!/2)2-5.. 2. 10, 790 55} Printeton, Nos 2-22. 2 8k | 5,917 25
Minot, .N; Dak... -¢.55-5¢ 25.2 10, 476 15a EalovAl ion Califa esas oneness 5, 900 55
Bucyrus; Oto. FAL 22h: 10, 425 100 || Fredericksburg, Va....-.-..-- 5, 882 50
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Chickasha, Okla..:......-.... 10,179 20: ||? Delphos, ‘Ohios.- 2222-322 - 5, 745 100
PMOTIgEN oY. iets 10, 169 60,1) ‘St. Marys, Ohio... ..-2.+..-3- 5, 679 100
Whitthe, Indi i22..54 22:2. 10, 145 160 ti Oberlin, Ohio! 22822-2222. 4 4, 236 10
AUsting Manni, = ce... 10, 118 65 || Brookings, S. Dak..........-. 3, 924 50
Connersville, Ind............. , 901 25 || Pullman, Wash.2.. 2.2204 2225. 2,440 45
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The flash process consists in heating rapidly to the pasteurizing
temperature, then cooling quickly. In this process the milk is heated
from 30 seconds to 1 minute only, usually at a temperature of 160°
F’. or above. In view of the previously mentioned requirements for
pasteurized milk this process should not be considered suitable for

. proper pasteurization. Several cities now prohibit the use of the
flash process for the pasteurization of milk.

In the holder process the milk is heated to temperatures of from
140° to 150° F. and held for approximately 30 minutes, after which
it is rapidly cooled. Sometimes the milk, instead of being held at a
certain temperature in one tank for 30 minutes, is merely retarded
in its passage through several tanks or other retarding device so that
the length of time required for the milk to pass through is about 30

SF minutes. In such cases, however, there is not always assurance that
all the milk is held for the desired time. The holder process has
almost entirely replaced the flash process, and is the one most used
in this country.

Pasteurization in bottles is the latest development of the process
to be used on a practical scale. This process, as first practiced, con-
sisted in putting the raw milk into bottles with water-tight seal caps,

107148°—22 2

10 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.

then immersing them in hot water until heated to 145° F. and hold-
ing them at that temperature for from 20 to 30 minutes. The cool-
ing was accomplished by gradually lowering the temperature of the
water until that of the milk reached 50° F.

The advantage of this process is in the fact that the milk after
heating is not exposed until it reaches the consumer, thereby elimi-
nating any danger of reinfection with disease-producing organisms
through handling. For this process to be successful, however, it is
necessary that the temperature of the milk in bottles be measured at
the bottom of the bottle, and that the holding period of 30 minutes’
begin when the temperature at the bottom has reached 145° F. This
is essential, because the milk in the top heats faster than that in
the bottom of the bottle.

The matter of seals is also important. They should be absolutely
water-tight, as the bottles are submerged in water, and during cool-
ing a defective cap might allow infection by polluted cooling water.
The disadvantage of this process is in the increased cost of pasteuri-
zation, caused by the cost of the seal caps. It is claimed, however,
that the saving in milk losses by pasteurization in bottles makes up
for the added expense of caps. It is now possible to pasteurize milk
in this manner without using water-tight caps. This is accomplished
by the aid of devices which fit over the tops and necks of the bottles,
thereby protecting the ordinary paper caps from the water which is
sprayed on the bottles for the purpose of heating or cooling. This
method of protecting the tops permits the use of the ordinary caps
and seems to remove the possible danger of polluted water infecting
the milk.

ADVANTAGES OF LOW-TEMPERATURE PASTEURIZATION.

In general, the trend of pasteurization has been toward the holder
process, and with this tendency the use of lower temperatures has
become more common. As a general rule, when the holder process
is used milk is heated to about 145° F. for from 20 to 30 minutes and
to at least 160° F’. for 1 minute when the flash process is used. From
bacteriological, chemical, and economical standpoints it is highly
desirable that milk be pasteurized at the lower temperature.

From a bacteriological standpoint, pasteurization at 145° F. for
30 minutes gives assurance, so far as we know, of a complete de-
struction of nonspore-forming disease-producing bacteria and at
the same time leaves in the pasteurized milk the maximum percent-
age of the bacteria that cause milk to sour (lactic-acid bacteria)
and only a small percentage of those that cause it to decompose
(peptonizers). When higher temperatures are used, while the total
number of all kinds of bacteria is reduced, the percentage of lactic-

STATUS OF PASTEURIZATION OF MILK. 11

acid bacteria becomes less and less and the peptonizing group in-
ereases until at 180° F., or above, the lactic-acid bacteria are prac-
tically destroyed and most of the bacteria left belong to the pep-
tonizing group. The heat-resistant lactic-acid bacteria which sur-
vive pasteurization at 145° F. for 30 minutes play an important
role in the souring of commercially pasteurized milk.

From a chemical standpoint, the advantage of the lower tempera-
ture is in the fact that milk pasteurized at 145° F. for 30 minutes
does not undergo any appreciable change which should affect its
nutritive value or digestibility. According to Rupp (26), the solu-
ble phosphates of lime and magnesia do not become insoluble and
the albumin does not coagulate. At 150° F. about 5 per cent of
the albumin is rendered insoluble, and the amount increases with
higher temperatures to 160° F., when about 30 per cent of the al-
bumin is coagulated. The heating period in Rupp’s experiments
was 30 minutes.

From an economic standpoint the advantages of pasteurization
at low temperatures is in the saving in the cost of heating and cool-
ing the milk. Bowen (10) has shown that the flash process of pas-
teurization requires approximately 17 per cent more heat than the
holder process. There is, of course, a correspondingly wider range
through which the milk must be cooled, which also adds to the
cost of pasteurization. This is owing to the fact that in the holder
process milk may be heated to 145° F. and held for 30 minutes,
while to obtain the same bacteriological reduction with the flash
process, with one-minute heating, the milk would have to be heated
to 165° F., and even then the complete destruction of disease-pro-
ducing bacteria might be questionable.

TEMPERATURES AND METHODS MOST SUITABLE FOR PASTEUR-
IZATION.

In view of the advantages of the lower temperature for heating
it is believed that the temperature of pasteurization should be
145° F. and that the milk should be held at that temperature
for 30 minutes. It has been found that heating at 140° F.
for that length of time will destroy pathogenic bacteria, provided
all the milk is heated to that point and held the full length of time.
But it has been shown by Schorer and Rosenau (27) that it is diffi-
cult to do this under commercial conditions. These investigators
tested the destruction of pathogenic organisms by inoculating milk
with B. diphtherie, B. typhi, and B. tuberculosis and pasteurizing
it in 100-gallon lots under commercial conditions. They found that

12 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.

sometimes the organisms were not all destroyed, and in this connec-
tion state:

Nothing in our experiments throws any doubt upon the thermal death points
of the microorganisms tested. We are sure that if the milk reaches 140° F.
and is held there for 20 minutes it will kill tubercle, typhoid, and diphtheria
bacilli. Our experiments show that milk pasteurized at this temperature for the
specific time may not always, in practice, reach these minimum requirements.
It is therefore evident that a liberal factor of safety is necessary in the opera-
tion of this type of pasteurizer under commercial conditions.

They state further:

Perhaps the best temperature to meet practical conditions is 145° F. and the
milk should be held from 30 to 45 minutes. This should give sufficient leeway.
If the pasteurizer is set at 145° F. care will probably be taken that it does
not go above 148° F. on account of destroying the cream line, and it is not likely
that the mixed milk in the holding tank would drop below 140° F., which is
the minimum.

Other experiments are reported by Pease and Heulings (in the
Report of the Committee on Milk Supply of American Public Health
Association, 1920), in which the destruction of pathogenic organisms
was tested under commercial conditions of pasteurization. Some of
the pathogenic types were found living after heating to from 140°
to 141° F. and holding for 15 minutes, but none were found alive after
30 minutes’ holding. Here again is evidence of the narrow margin
of safety when milk is pasteurized at 140° F. for 30 minutes, and
the committee expressed the following opinion:

The committee feels that while enough has been done to indicate clearly that
a proper application of heat to a temperature of 140° F. for a minimum period
of 30 minutes will destroy substantially all the pathogenic bacteria in milk,
still they believe, as already expressed, that a margin of safety for biological
reasons calls for the use of higher temperatures of not lower than 145° F.

The United States Department of Agriculture, since 1910, (2) has
advised the use of a temperature of 145° F. for a period of 30 minutes
for the pasteurization of milk. Besides insuring an ample margin of
safety, a temperature of 145° F’. causes a considerably greater destruc-
tion of bacteria in milk than 140° F. when held for the same period
of 80 minutes.

Extensive experiments (3) in the research laboratories of the
Dairy Division have shown that the thermal death point of a con-
siderable number of bacteria lies between 140° and 145° F.; there-
fore an increase of 5° above 140° F’. produces a great increase in the
destruction of bacteria.

There is a marked tendency in commercial work to pasteurize at
or near the minimum temperature requirement necessary to destroy
pathogenic organisms, namely, 140° F. Such seems to be the case
because of the fear of injuring the cream line. In fact, the opinion
is often expressed by milk-plant operators that a temperature of

STATUS OF PASTEURIZATION OF MILK. 13

145° F. can not be used because of the marked loss in cream line.
Harding (19) has studied the effect of temperature on the cream line
in a number of different plants throughout the country, and has come
to the following conclusion:

The data here presented show that the volume of cream on milk begins
measurably to decrease when the temperature of pasteurization rises from 142°
F. to 144° F. As the temperature goes higher, the decrease in the volume of
cream becomes rapidly more pronounced ; at 145° F. it amounts to slightly more
than 10 per cent by volume; at 146° F. it amounts to 16.6. per cent; and at
148° F., to approximately 40 per cent.

It may be said, however, that there are plants in this country, in-
cluding some of the largest, in which milk is successfully pasteurized
at 145° F’., and this temperature is maintained for 30 minutes. It is
also interesting to note that at the 1921 meeting of the International
Dairy and Milk Inspectors’ Association, Pease reported experiments
carried on by Heulings and him which showed that pasteurization at
145° F. for 30 minutes did not decrease the cream line when the milk
was properly heated and cooled.

The method of pasteurization, whether it is the holder or in-the-
bottle process, is not so important provided the process is such that
the milk is heated to 145° F. and that all of it is held for 30 minutes.
The great majority of plants pasteurize by the holder process, and it
is gratifying to observe that the flash process is but little used.
Replies to a questionnaire sent to numerous cities in this country
showed only 33 plants using the flash process in 18 cities out of the
966 which supplied information on this subject. Five cities reported
that the flash process was not allowed, while one permitted its use
but would not allow the milk to be labeled “ Pasteurized.” ?

SUPERVISION OF THE PROCESS.

Intelligent supervision of the pasteurizing process is absolutely
necessary and can not be provided unless there is a thorough knowl-
edge of the primary object of pasteurization and the bacteriological
principles involved.

The primary object is the destruction of any disease-producing
bacteria which may be in the milk and the handling of the pasteurized
milk in such manner that it can not be reinfected. When this object
is accomplished it is found that a large percentage of the bacteria
in the milk are destroyed and its keeping quality greatly improved.

The primary object can be accomplished by heating all the milk to
145° F. and holding it for a period of 30 minutes. It is then only
necessary to cool the milk immediately over thoroughly cleaned and

2For information on pasteurizing equipment the reader is referred to United States
Department of Agriculture Bulletin No. 890, Milk-Plant Equipment.

107148°—22 3

14 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.

steamed coolers, to run into thoroughly cleaned and steamed, or other-
wise sterilized, bottles through a thoroughly cleaned and sterilized
bottle filler, then to cap the bottles with sterilized caps and place the
milk in low-temperature refrigerators.

This process sounds relatively simple, yet at every step problems are
encountered which may defeat the primary object.

First of all, it must be kept in mind that bacteria are too small to
be seen by the naked eye and that they are distributed in the air of
the milk plant, upon the equipment with which milk comes in contact,
and upon the hands of employees. Flies also carry millions of bac-
teria. When milk comes to the plant to be pasteurized the logical
thing to do is to see that it comes in contact only with apparatus
which has been thoroughly cleaned and thoroughly steamed. The
equipment may appear clean, but since bacteria can not be seen
with the naked eye, a clean (to the eye) tank or pipe may contain
many millions. Means must be taken to destroy as many of them as
possible. To do this steam is usually employed, for steam at 205° F.
or above for a period of 2 to 5 minutes will destroy disease-producing
bacteria and all but spores of the harmless types. Equipment so
treated may be called bacteriologically clean, but must be visibly
clean before application of the steam if satisfactory results are to be
expected.

When the equipment is in this condition, the milk can be pasteur-
ized. At this point the object is to heat all the milk to 145° F. and
hold it for 30 minutes. In intelligent supervision many problems
are encountered at this step in the process. They are well dis-
cussed in a paper entitled Pasteurization of Milk, which is a report
of the Committee on Milk Supply of the Sanitary Engineering Sec-
tion of the American Public Health Association, 1920. Briefly, the
principal points are:

1. Heat all the milk to 145° F.

2. Hold all the milk for 30 minutes. (Some continuous-flow systems do
not do this.)

3. Watch for leaking valves, also pipe lines which hold milk below the pas-
teurizing temperature.

4. Have accurate recording thermometers so arranged as to show the total
heating period. Recording thermometers should be frequently checked against
a standard thermometer of unquestionable accuracy.

5. Watch for foam on the milk. This may stay in the vats for hours at a
warm temperature suitable for bacterial development.

After proper heating and holding, the pathogenic organisms have
been destroyed and the total number of bacteria reduced to a mini-
mum point. The next problem is to cool and bottle the milk with-
out reinfection, particularly with disease-producing bacteria.

STATUS OF PASTEURIZATION OF MILK. “5

To do this, bacteriologically clean coolers, bottle fillers, bottles,
and sterilized caps are necessary; and what is of greatest importance
is to see that the pasteurized milk does not come in contact with
human hands, or with apparatus, including bottles and caps, touched
by the hands after being sterilized. The hands of milk handlers
constitute perhaps the most dangerous source of reinfection in the
plant, for they may convey pathogenic organisms. Through such
channel milk may be contaminated by carriers of many diseases.

In order to guard against such possibilities, all employees who
handle apparatus or milk in the plant or during delivery should
undergo frequent medical examination, and any diseased persons
or carriers should be prevented from working in positions in which
they have even indirect contact with milk, milk equipment, or deliv-
ery of the product.

It is perhaps unnecessary to say that flies are also a very serious
menace to the milk supply. They must be kept out of milk plants,
for it is impossible to tell when they may infect the milk. This in-
fection can occur directly by flies getting into the milk or indirectly
through contamination of equipment or containers.

At every step in the pasteurization of milk, one is compelled to
think of the process in terms of bacteria in order to supervise it
intelligently.

HANDLING MILK AFTER PASTEURIZATION.

Pasteurization of milk destroys about 99 per cent of the bacteria;
consequently the milk is not sterile. On account of this fact, pas-
teurized milk is still a perishable product, and must be handled
with the same care as raw milk. This is a point for both the con-
sumer and the milkman to remember.

Milk after pasteurization should be cooled to about 40° F. and
kept at that temperature until delivery. During warm weather it
should be iced on the delivery wagons. From a sanitary standpoint
all milk, whether raw or pasteurized, should be delivered as soon as
possible, in order that the consumer may get it in the best condition.
In the best pasteurized milk, when held at about 40° F., there is only
a slight bacterial increase during the first 24 hours. In many cases
the pasteurization and delivery may be so arranged that the con-
sumer gets the milk before much, if any, change has taken place in
the bacterial content. For the benefit of the consumer the word
“ Pasteurized ” should be printed on the cap, as it is only right for
him to know whether he is using raw or pasteurized milk. Some people
object to pasteurized milk, especially for infant feeding, while others
desire it. It has been the experience of numerous milk dealers that
the labeling of their product has greatly increased their trade.

16 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.
COST OF PASTEURIZING MILK.

The present cost of pasteurization has been estimated by Bowen
from the cost given in his earlier paper (10) on the assumption that
the average price of coal has increased 2.04 times and that milk-
plant labor and equipment have increased 50 per cent over the prices
of 1913, the year in which his paper was written. He obtained the
information from a series of tests in five establishments which were
considered to represent the average city milk plant. The pasteuriz-
ing equipment in each consisted of a heater, a holding tank, a
regenerator, and a cooler. The cost of operation was based on the
pasteurizing cycle, starting with the initial temperature of the raw
milk and raising it to the pasteurizing temperature, then cooling to
the initial temperature of the raw milk. He based the costs on daily
interest at 6 per cent per annum on capital invested in pasteurizing
equipment, and depreciation and repairs per day at 25 per cent
per annum; interest per day at 6 per cent per annum on capital
invested in mechanical equipment for pasteurizing, such as engines,
boilers, etc., and depreciation and repairs per day at 10 per cent per
annum. Other costs figured were labor, coal now estimated at $8.16
a ton, cooling water now estimated at $0.75 per 1,000 cubic feet, and
refrigeration now estimated at $2 a ton. With these new estimates
substituted for the old figures, Bowen calculates that the average
cost of pasteurizing 1 gallon of milk is approximately $0.0049, or a
little less than one-half cent.

BACTERIA WHICH SURVIVE PASTEURIZATION.

It has been stated that about 99 per cent of the bacteria in milk
are destroyed by pasteurization; consequently about 1 per cent of
the bacteria remain alive, and the kinds left depend entirely on the
temperature to which the milk is heated and the number of heat-
resistant bacteria in the milk. From studies of the bacteria which
survive pasteurization, it is possible to show graphically the hypo-
thetical relations of the bacterial groups in raw milk and in milk
pasteurized by the holder process at various Taal under
laboratory conditions.

The bacterial flora of the various kinds of milk is represented in
Figure 1 by columns of equal length divided into sections, which, in
a general way, show the relative proportion of the bactoual groups.

From the figure it may be seen that raw milk contains four prin-
cipal groups of bacteria—the acid, inert, alkali, and peptonizing.
The acid group is divided again into two—the acid-coagulating,
which coagulates milk within 14 days, and the acid group, which
merely produces acid and does not coagulate it in less time than that.
In raw milk the inert group is the largest.

In milk pasteurized at 145° F. the great increase in the proportion

MILK.
of the acid-coagulating and acid groups is plainly shown.

STATUS OF PASTEURIZATION

The per

At this

At 160° F,

the total-acid group is still the largest, but the acid-coagulating

cent of the alkal and peptonizing groups is reduced.
group is made up of bacteria which coagulate very slowly.

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Fic. 1.—The hypothetical relation of the bacterial group to raw and pasteurized milk,

At 170° F. the total-acid group remains

about the same, but the organisms produce acid and coagulate the
The alkali group is practically destroyed although

temperature the alkali group is greatly reduced, and the peptonizing

reduced to the minimum.

milk very slowly.

18 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.

occasionally a sample may show a fairly high per cent. The most
important change is in the peptonizing group. At this temperature
the ratio of this group to the total number- of bacteria begins to
increase. The increase when milk is pasteurized at 180° F. is even
more striking. At this temperature more than 75 per cent of the
bacteria which survive are peptonizers. No organisms of the acid-
coagulating group are found, and only a small per cent of the acid
group. Occasionally a few of the alkali group may be found. At
190° F. and 200° F. the bacterial groups which survive are about the
same in their relative sizes as at 180° F.

It is very evident that when the bacterial flora of pasteurized milk
is under discussion the temperature of the process is of fundamental
importance. From Figure 1 the bacterial groups left in milk pas-
teurized at different temperatures may be seen at a elance. It must
be remembered, however, that the relations of the bacterial groups
represent only average conditions and that the bacterial flora of every
sample of milk must not be expected to conform exactly to these
averages. Variations in methods and conditions in the production of
milk may considerably influence the bacterial group relations of an
individual sample.

The results in Figure 1 may perhaps be better explained in popular
terms. When milk is pasteurized at 145° F. for 30 minutes, most
of the bacteria (lactic-acid) left alive in it are of the kind which
cause it to sour, and there are present only a few bacteria (pep-
tonizing) which cause it to decompose. As the milk stands, the acid
formers grow and cause the milk to sour instead of decompose.
When milk is pasteurized at 180° F. for 30 minutes, however, the bac-
teria (lactic-acid) which cause the souring of milk are practically all
destroyed, and those which are alive (peptonizing) continue to grow
and cause the milk to decompose.

Not only do certain types of lactic-acid bacteria survive pas-
teurization but some also grow at the pasteurizing temperature.
Sometimes upon long-continued heating at 140° to 145° F. for
several hours, milk sours in the holding tanks due to the growth
of these organisms. The ordinary period of holding does not provide
‘sufficient time for their development, so this type of souring 1s not
encountered in milk plants except when there is an interruption
in the pasteurizing process due to some abnormal condition.

SURVIVAL OF STREPTOCOCCI.

Since the general groups of bacteria which survive pasteuriza-
tion have been discussed, let us now consider a more specific group.
It has been the custom of some authorities to consider the presence
of streptococci in pasteurized milk an indication of an ineffective
process, As already pointed out, pathogenic streptococci are readily

STATUS OF PASTEURIZATION OF MILK. 19

destroyed by proper pasteurization. In a study of the subject (4),
however, it was found that certain strains of streptococci are able
to survive pasteurizing temperatures.

The thermal death points of 139 cultures of streptococci isolated
from cow feces, from the udder and mouth, and from milk and cream,
showed a wide variation when the milk was heated for 30 minutes
under conditions similar to pasteurization. At 140° F., the lowest
pasteurizing temperature, 89 cultures, or 64.03 per cent, survived;
at 145° F’., the usual temperature for pasteurizing, 46, or 33.07 per
cent, survived ; and at 160° F., 3 cultures, or 2.16 per cent, survived ;
all these were destroyed at 165° F. The streptococci from the udder,
on the whole, were less resistant and those from milk and cream
more resistant to heat than those from the mouths and feces of
the cows.

Two classes of streptococci seem to survive pasteurization: (1)
Streptococci which have a low majority thermal death point (the
temperature at which a majority of the bacteria are killed), but
among which a few cells are able to survive the pasteurizing tem-
perature. This ability of a few bacteria may be due to certain
resistant characteristics peculiar to them or it may be caused by
some protective influence in the milk. (2) Streptococci which have
a high majority thermal death point, and which, when such is the
case, survive because this point is above the temperature of pas-
teurization. This ability to resist destruction by heating is a per-
manent characteristic of certain strains of streptococci.

These streptococci which have a high thermal death point above
the pasteurizing temperature undoubtedly play an important part
in the occasional high counts found in pasteurized milk. Such
counts are sometimes observed when the count of the raw milk runs
the same as usual. As the proportion of these heat-resistant types
vary in milk their numbers may at times reach such figures that
their survival of the pasteurizing process gives an abnormally high-
count product. The presence and variation of their numbers in milk
therefore is a matter which must be given consideration in connec-
tion with bacteria standards for pasteurized milk. 1

It is evident that certain varieties of streptococci are able to survive
pasteurization, while others are probably always destroyed. Numer-
ous investigators have studied the thermal death point of streptococci
isolated from patients having septic sore throat and have found that
the organism was destroyed by pasteurization at 145° for 20 minutes.
These results, together with the protection which proper pasteuriza-
tion seems to afford against epidemics of that disease caused by milk
supplies, indicate that the varieties of streptococci associated with or
responsible for the disease are among the varieties which have a low
thermal death point.

20 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.
THE COLON TEST FOR EFFICIENCY OF PASTEURIZATION.

In a study (6) of the ability of colon bacilli to survive pasteuriza-
tion it was found that certain strains could survive pasteurization at
145° F. for 30 minutes. On examining 174 cultures of colon bacilli it
was found that at 140° F., the lowest pasteurizing temperature, 95
cultures survived; at 145° F., the usual temperature for pasteuriza-
tion, 12 survived. In each case the heating period was 30 minutes.
Considerable variation was observed in the thermal death point of
the colon bacilli which survived at 145° F. When the cultures which
withstood the first heating were again heated it was found that many
did not survive, and in each subsequent heating different results
were obtained. Colon bacilli have a low majority thermal death
point but on account of the resistance of a few cells, they may survive
the pasteurizing process.

The colon test as an index of the efficiency of the process of
pasteurization is complicated by the ability of certain strains to
survive a temperature of 145° F. for 30 minutes and to develop
rapidly when the pasteurized milk is held under certain tempera-
ture conditions met during storage and delivery. Consequently
the presence of a few colon bacilli in pasteurized milk under ordi-
nary market conditions does not necessarily indicate that the milk
was not properly heated. The presence of a large number of colon
bacilli immediately after the heating process indicates that the milk
has not been heated to 145° F. for 30 minutes and the test properly
applied should be valuable in control work. Fermentation tubes
can be used for making the test, but when gas formation is noted
the presence of colon bacilli should be demonstrated by further tests.
Often anaerobic spore formers are encountered which survive pas-
teurization and give the typical fermentation tube test.

PAST AND PRESENT THEORIES OF PASTEURIZATION.

Pasteurization at present is looked upon with favor by medical
men, sanitarians, dairymen, and consumers, but the art has not been
developed without opposition, and its value is not universally ac-

cepted. Most of the objections to pasteurized milk have been based

on theory or on experiments in which the milk was pasteurized at
high temperatures. In view of our modern theories they are of no
ereat importance. j

One of the greatest objections to pasteurized milk has been that
the heating destroyed the lactic-acid bacteria and that putrefactive
organisms were left, which, when relieved from the restraining action
of the acid-forming bacteria, would develop, forming toxins and
putrefactive products. It was believed that the milk, because it
was not sour, would be consumed in that condition. This objection

< _

STATUS OF PASTEURIZATION OF MILK. 21

was based on experiments in which milk was heated to temperatures
near the boiling point and can not be applied to milk pasteurized at
low temperatures. From the results of many years’ work in the
Dairy Division on commercial pasteurized milk, it has been found
that such milk sours, as raw milk does, but that the souring is
delayed when compared with the souring of the same grade of raw
milk. Pasteurized milk sours in a manner similar to that of a high
grade of raw milk, and there is no more reason to fear the over-
growth of putrefactive organisms than there is in any high-grade
milk. Pasteurization for 30 minutes at temperatures of about 145°
F., as is generally practiced in this country, does not destroy all
the lactic-acid organisms, and those which survive play an important
role in the souring of commercially pasteurized milk.

Another objection to pasteurized milk has been that bacteria grow
faster in it than in raw milk. In spite of several experiments which
seem to prove this point, it has never been thoroughly established.
It has been found that the rate of bacterial increase is approximately
the same when the comparison is made between raw milk and pasteur-
ized milk having about the same bacterial content.

It is often stated that pasteurization, even if it does destroy
bacteria, does not destroy poisonous products of their growth. This
can hardly be considered a real objection, for if they are present in
raw milk they must be consumed with it, and if pasteurization does
not destroy them the pasteurized milk would be no worse than raw
milk.

The question as to whether pasteurization destroys beneficial
enzyms is still an open one. In the light of our present knowledge
of the enzyms in milk and the part they play in the digestive process
it is quite impossible to settle the question of their importance. It
is evident, however, that the low temperatures now in use in pasteuri-
zation have little effect on the commonly recognized enzyms.

The opponents of pasteurization have raised an objection on the
ground of its direct influence on the milk producer. It has been
asserted that pasteurization would cause lax methods of production
on the farm, for the reason that farmers would know that the milk
was to be pasteurized and, therefore, they could be careless in its pro-
duction. There seems to be some basis for this objection, but in any
city where there is any inspection of the raw-milk supply the same
inspection can and should be continued even though the milk is to
be pasteurized.

From a chemical standpoint serious objections have been raised
against pasteurized milk, because the heating produces changes which
render the milk less digestible, particularly in the case of infants.
As has already been stated, however, Rupp (26) has found that milk

22 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.

pasteurized at 145° F. for 30 minutes does not undergo any appreci-
able chemical change. He found that soluble phosphates do not
become insoluble, that the albumin does not coagulate, and that when
higher temperatures are used chemical changes do occur. He also
developed the fact that 5 per cent of the albumin is rendered insoluble
in milk heated for 30 minutes at 150° F., while at 160° F. 30.78 per
cent of the albumin is coagulated. Further evidences that low-tem-
perature pasteurization does not injure the digestibility and nutritive
value of milk are shown by the results of feeding experiments with
babies. According to Weld (31), a number of babies that were fed
raw milk and pasteurized milk showed only a slight difference in
the average net daily gain in weight during the feeding period. The
slight difference was in favor of pasteurized milk. Hess (21), how-
ever, has found that milk pasteurized for 30 minutes at 145° F. may
cause, in infants, a mild form of scurvy, which yields readily to so
simple a remedy as orange juice.

High-temperature pasteurization of earlier days must not be con-
fused with low-temperature pasteurization of the present day. Many
of the objections which have been raised to pasteurization have been
founded on the observation of milk heated to high temperatures.
The fallacy of the objections to pasteurization have been shown,
however, through scientific research in the last few years, and as a
result the value of the process has.been firmly established.

PASTEURIZATION AND VITAMINS.

The discovery of vitamins within recent years has shown how im-
possible it is to estimate nutritive requirements solely in terms of
digestible protein, carbohydrate, fat, and inorganic salts. But little
is known of the real chemical nature of vitamins, except that they are
necessary for normal growth and health. Three vitamins are now
recognized, known as vitamin A (soluble in fat) and vitamins B
and C. (soluble in water). Most authorities now agree that fat-
soluble A and water-soluble B are essential for growth, and water-
soluble C, the antiscorbutic vitamin, may also play a part in this
relation.

Because of the limited character of the infant’s diet the vitamin
content of its food is more important than that of the adult’s, as the
latter has a great variety of foods. Fortunately, milk has been
found to be a food containing the three vitamins and the effect of
pasteurization on the vitamin content is of importance.

Fat-soluble A and water-soluble B have been found to be quite
resistant to heat, and it is agreed that pasteurization has little or
no effect upon them. The antiscorbutic vitamin C, however, is quite
sensitive to heat above 122° F. While the destruction of this vita-

STATUS OF PASTEURIZATION OF MILK. 23

min depends upon the temperature, length, and condition of heat-
ing, as well as the reaction of the material in which it exists, there
seems to be little doubt that pasteurization of milk, under usual com-
mercial conditions, at 145° F. for 30 minutes, weakens the antiscor-
butic property of the milk.

Hess and Fish (20), in 1914, in studying scurvy in children found
that some cases of scurvy developed when milk was used which had
been pasteurized at 145° for 30 minutes.

After further studies on this subject Hess (22) made the following
statement:

Although pasteurized milk is to be recommended on account of the security
which it affords against infection, we should realize that it is an incomplete
’ food. Unless antiscorbutics, such as orange juice, the juice of an orange peel,
or potato water is added, infants will develop scurvy on this diet. This form
of scurvy takes some months to develop and may be termed subacute. It must
be considered not only the most common form of this disorder, but one which
passes most often unrecognized. In order to guard against it, infants fed ex-
clusively on a diet of pasteurized milk should be given antiscorbutics far earlier
than is at present the custom, even as early as the first month in life.

In the course of the development of infantile scurvy, growth both in weight
and in length is markedly affected. Under these conditions weight ceases to
increase, and a stationary plane is maintained for weeks or for months. There
is quick response, however, on the administration of orange juice or its equiva-
lent; indeed supergrowth is thereupon frequently manifested.

PASTEURIZED MILK FOR INFANTS.

A rational view must be taken of the use of pasteurized milk.

Shall the protection against infection, which is made available by
the proper pasteurization of milk, be discarded because of its defi-
cient antiscorbutic property, or shall its protection be accepted and
the deficiency in vitamin C be made up by feeding orange juice or
other antiscorbutics ?
_ Perhaps the feeding of infants calls for even further thought than
is generally given. As Eddy (14) in his recent book points out, there
are two points to be kept in mind in infant nutrition. The first is
that the vitamin content of cow’s or human milk is dependent pri-
marily on the food eaten by the producer of the milk. In other
words, milk is merely a mobilization of vitamins eaten, and if the
diet is to yield a milk rich in vitamins the food eaten must also be
rich. He further points out the fact that cereals are poor in vitamins
and green grasses rich in them, and that this brings up the question
of winter feeding if the milk supply is used for infants, and he sug-
gests that the variability in vitamins A and B in milk may at times
make it necessary to supplement the diet.

The second point brought out by Eddy expresses what appears to
be the most reasonable attitude toward the use of pasteurized milk

24 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.

for infant feeding according to our present knowledge of vitamins,
and it is therefore quoted:

The second point in regard to milk lies in the effect of pasteurization. This
measure is now well-nigh universal and in America at least has played a tre-
mendous part in the reduction of infant mortality, especially in the summer
months. At present, however, we know that this treatment while removing
dangerous germs may also eliminate the antiscorbutie factor. The sensible
attitude then is to recognize this fact and if a clean whole milk is not available
retain the pasteurization and meet the vitamin deficiency by other agents.
Such agents are orange juice and tomato juice, and experience has already
shown that these juices can be well tolerated by infants much earlier than
used to be thought possible.

It seems, therefore, that the only serious effect of pasteurization
on the vitamins is on the antiscorbutic vitamin C, and it is evident
that the feeding of orange or tomato juice, or other antiscorbutic,

readily makes up for the deficiency of this vitamin in pasteurized
milk.

THE NECESSITY FOR PASTEURIZATION.

The need for safeguarding the milk supply is amply proved by
the numerous epidemics traced to milk. Trask (29) reported 179
epidemics of typhoid fever from 1881 to 1907, of which 107 were in
the United States, 51 epidemics of scarlet fever, including 25 in this
country, during the same period, and 23 epidemics of diphtheria
from 1879 to 1907, including 15 in the United ‘States. These were
all traced to milk. He also listed 7 epidemics of sore throat, most
of which occurred in England. Since 1907 several epidemics of
septic sore throat have been traced to milk. Among these may be
mentioned the epidemics at Boston, Chicago, and Baltimore, and
others which have occurred in smaller cities.

The problem of pasteurization is not based simply on the question
of which is preferable, raw or pasteurized milk, but rather upon the
most economical and practical way of producing a safe milk supply.

In connection with the possibility of transmission of disease
through the agency of milk, certain fundamental facts must be
recognized.

1. That such possibilities exist as demonstrated by epidemics of the past.

2. That certain diseases transmitted to man, such as tuberculosis, may come
from diseased animals. The danger from this source can be prevented by the
elimination of tuberculous cattle from producing herds on the basis of the
tuberculin test.

3. That the freeing of the herds from tuberculosis offers no protection against
other diseases, as typhoid fever, diphtheria, and septic sore throat, because the
pathogenic organisms causing these diseases may come from infected water sup-
plies or probably in most cases from human carriers of disease.

The term “carriers” is used to designate persons who carry the
disease-producing bacteria. In the case of diphtheria, carriers har-

STATUS OF PASTEURIZATION OF MILK. 25

bor the diphtheria organisms and discharge them from the nose or
throat. Typhoid carriers discharge typhoid bacilli in their feces or
urine. Diphtheria carriers may become so after having an acute
attack of the disease or from other carriers. Typhoid carriers are
particularly important, because from 2 to 4 per cent of the persons
who have had typhoid fever continue, as evidence shows, to discharge
the typhoid bacilli in their feces or urine or both and become chronic
carriers.

Persons suffering from sore throat are a menace to the milk
supply, and probably the organisms responsible for septic sore throat
are sometimes carried in the throat of apparently normal individuals.

Tt is manifestly impossible to have a medical examination of all per-
sons engaged in producing and handling milk. Yet such examinations
at frequent intervals would be necessary, together with tuberculin
testing and the assurance of unpolluted water supplies on every farm,
in order to safeguard the milk supply of the Nation to the same
extent that is now possible by proper pasteurization. The apprecia-
tion of the need for pasteurization is distinctly shown by the marked
increase in pasteurization in the United States.

REFERENCES TO LITERATURE.

ANDERSON, A. K., and FINKELSTEIN, R.
(1) 1919. A study of the electro-pure process of treating milk. Jn Jour.
Dairy Science, v. 2, no. 5, p. 374-406.
Ayegs, S. H., and JoHNSON, W. T., jr.

(2) 1910. The bacteriology of commercially pasteurized and raw market
milk. U.S. Dept. Agr., Bur. Anim. Indus. Bul. no. 126.

(3) 1913. A study of the bacteria which survive pasteurization. U. S.
Dept. Agr., Bur. Anim. Indus. Bul. no. 161.

(4) 1914. Ability of streptococci to survive pasteurization. Jn U. S.
Dept. Agr., Jour. Agr. Research, v. 2, no. 4, p. 321-3830.

(5) 1914. The destruction of bacteria in milk by ultra-violet rays. Jn
Centbl. Bakt. [ete.], Abt. 2, Bd. 40, No. 1/8, p. 109-131.

(6) 1915. Ability of colon bacilli to survive pasteurization. Jn U. 8.

Dept. Agr., Jour. Agr. Research, v. 3, no. 5, p. 401-410.
and Davis, B. J.

(7) 1918. The thermal death point and limiting hydrogen ion concentra-
tion of pathogenic streptococci. In Jour. Infec. Diseases, y. 23, no.
3, p. 290-300.
BEATTIE, J. M.
(8) 1916. The electrical treatment of milk for infant feeding. Jn Jour.
State Med., London, v. 24, no. 4, p. 97-118.
(9) 1920. On the destruction of bacteria in milk by electricity. Gt. Brit.
Med. Research Committee, Spec., Rpt. no. 49.
BoweEN, J. T.
(10) 1914. The cost of pasteurizing milk and cream. U. S. Dept. Agr.,

Bul. no. 85.

(11)

(12)

(13)

(14)

(15)

(16)

(17)

(18)

(19)

(20)

(22)

(23)

(24)

(26)

(27)

BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE.

Bray, H. A.

1915. A milk borne epidemic of tonsillitis in tuberculous patients.

In Jour. Amer. Med. Assoc., v. 64, no. 14, p. 1127-1130.
Capps, J. A., and MILter, J. L.

1912. The Chicago epidemic of streptococcus sore throat and its re-
lation to the milk supply. Jn Jour. Amer. Med. Assoc., v. 58, no. 24,
p. 1848-1852.

Davis, D. J.

1918. The relation of streptococci to bovine mastitis and septic sore

throat. In Amer. Jour. Pub. Health, vy. 8, no. 1, p. 4046.
Eppy, W. H.

1921. The vitamine manual. Williams & Wilkins Co., Baltimore,
Md.

EVANS, ALICE C.

1916. The bacteria of milk freshly drawn from normal udders. In
Jour. Infect. Diseases, v. 18, no. 5, p. 437-476.

1917. The large number of Bact. aborius var. lipolyticus which may
be found in milk. Jn Jour. Bact., v. 2, no. 2, p. 185-186.

HAMBURGER, L. P.

1912. An epidemic of septic sore throat in Baltimore and its relation
to a milk-supply, a preliminary report. Jn Jour. Amer. Med. Assoc.,
v. 58, no. 15, p. 1109-1111.

1913. The Baltimore epidemic of streptococcus or septic sore throat
and its relation to a milk supply. Jn Bul. Johns Hopkins Hosp.,
v. 24, no. 263, p. 1-11.

HARDING, H. A.

1921. Effect of temperature of pasteurization on the creaming ability

of milk. Univ. of Illinois Agr. Exp. Station Bul. 237.
Hess, A. F., and FisH, M.

1914. Infantile scurvy: The blood, the blood-vessels, and the diet.

In Amer. Jour. Diseases Children, v. 8, no. 6, p. 385-405.
Hess, A..F...

1915. Infantile scurvy. II. A new aspect of symptomatology, path-
ology, and diet. Jn Jour. Amer. Med. Assoc., v. 65, no. 12, p. 1003-
1006.

1916. Infantile scurvy. III. Its influence on growth (length and
weight). Jn Amer. Jour. Diseases Children, v. 12, no. 2, p. 152—165.

JORDAN, E. O.

1913. The municipal regulation of milk supply. In Jour. Amer. Med.

Assoc., v. 61, no. 26, p. 2286-2291.
KRUMWIEDE, C., and Nose, W. C.

1921. On the claim that some typhoid-paratyphoid strains survive
the milk pasteurization. In Jour. Infect. Diseases, v. 29, no. 3, p.
310-812.

Mounier, J. R.

1909. Conditions and diseases of the cow injuriously affecting the

milk. In U. S. Hyg. Lab. Bul. no. 56, p. 501-526.
Rupp, PHILIP.

1913. Chemical changes produced in cows’ milk by pasteurization.

U. S. Dept. Agr., Bur. Anim. Indus. Bul. no. 166.
ScHoreER, E. H., and ROSENAU, M. J.

1912. Tests of the efficiency of pasteurization of milk under prac-

tical conditions, Jn Jour, Med, Research, v, 26, no, 1, p, 127-158.

(28)
(29)
(30)

(31)

STATUS OF PASTEURIZATION OF MILK. 27

THORNTON. W. M.

1912. The electrical conductivity of bacteria and the rate of steriliza-
tion of bacteria by electric currents. Jn Proc. Roy. Soc., London,
Ser. B. Biological Sciences, v. 85, no. B 580, p. 331-344.

TRASK, J. W.

1909. Milk as a cause of epidemics of typhoid fever, scarlet fever,

and diphtheria. In U. S. Hyg. Lab. Bul. no. 56, p. 25-149.
Twiss, EpitH M.

1920. The effect of pasteurizing temperatures on the paratyphoid

group. Jn Jour. Infect. Diseases, v. 26, no. 2, p. 165-170.
WELD, I. C.

1912. George M. Oyster, jr. Baby milk philanthropy, report for the

first 18 months beginning Apr, 24, 1911, and ending Oct, 24, 1912.

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