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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.

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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.

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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 Connellsville; Pace ost. 13, 804 50 || Chippewa Falls, Wis......... 9, 130 50 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 iatesnpre We ne ge oe 10, 909 50. || Greenwich, Conn..........:.- 5, 939 75 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 ae HOH. 5. ee Ee v3 10, 305 (oll ollevaie sO nig N= sass aoe 5, 776 75 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 aitnerson., Nod 2s. ov 9,497 OF lieDavis. Cali 2. oe 1, 500 97 Webster Grove, Mo........... 9,474 44 ||

|

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.

i

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.

17

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

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

OF

STATUS OF PASTEURIZATION

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At this

At 160° F,

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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

é

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.

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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.

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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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