¥ a. - “yr oie, Moet hy 4 Y Piel ta Ae en fit nye «an ees ae } ” ag : Yedda’ he ne - . te 4 ‘ om , rw | ” we, Pa ALBERT R. MANN LIBRARY AT CORNELL UNIVERSITY : FORNELL UNIVERSITY LipRary Cornell University The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http:/Awww.archive.org/details/cu31924062824036 PASTEURIZATION OF MILK Rapes of Commitee on Milk Supply : OF THE _ Sanitary Engineering. Section American Public Health Association - : ‘Committee’ H, A. Whittaker, Chairman H).D. Pease —- S. M.Heulings | A, F.. Stevenson Mayo,Tolman— Ralph E. Irwin (Associate) PRICE 35c, 2 BOSTON _ AUGUST, 1920 - ~PASTEURIZATION OF MILK Report of Committee on Milk Supply OF THE Sanitary Engineering Section American Public Health Association Committee H. A. Whittaker, Chairman H. D. Pease S. M. Heulings A. F, Stevenson Mayo Tolman Ralph E.. Irwin (Associate) PRICE 35c BOSTON AUGUST, 1920 | $ C@IR Wh E. AMERICAN PUBLIC HEALTH ASSOCIATION SANITARY ENGINEERING SECTION REPORT OF COMMITTEE ON MILK SUPPLY I. Inrropuction,. The Committee has limited its activ- ities to certain subjects on the pasteur- ization of milk which have a bearing on public health, and has attempted to bring together certain information on milk pasteurization which will be of service to health officials and others interested in the subject. The mem- bers of the Committee submitted re- ports on the following divisions of the work: The Present Status and Control of Milk Pasteurization, Mr. H. A. Whittaker; The Effect of Pasteuriza- tion on the Composition of Milk, Mr. Albert F Stevenson; The Mechanical Features of Pasteurization Plants and Responsibility of Operation, Mr. S. M. Heulings; The Analytical Control of Pasteurization Plants, Dr. H. D. Pease; and The State and Municipal Supervision of Milk Pasteurization, Mr. Mayo Tolman. These reports were re-arranged and co-ordinated by the Chairman, Mr. H. A. Whittaker. Mr. R. E. Irwin was made an associate member of the Committee in October, 1919, after the present report was pre- pared. He has carefully reviewed the report and offered certain suggestions. II. Tue Present Status or Mitk PASTEURIZATION. Inquiries were sent to all states and territories of the United States and the provinces of the Dominion of Can- ada requesting information regarding the number of pasteurization plants in operation and the control exercised over the pasteurization of milk for human consumption. Sixty-three ques- tionnaires were sent out to which 43 replies were received. (1) Number of Plants in Operation. In regard to the number of pasteuriza- w -cial Control. tion plants, fifteen replied that no rec- ord was available, while twenty-eight provided information which showed a total of 1,750 plants in operation. In view of the fact that the 28 replies were from various sections of the United States and Canada, and might be considered as representative of the entire territory, it may be estimated that there are roughly 4,200 pasteuri- zation plants in operation for, the treat- ment of milk for human consumption in these countries at the present time. (2) State, Territorial, and Provin- The information received on state, territorial, and provincial con- trol of pasteurization showed that ten had either laws or regulations on the subject, while thirty-six had no legal authority. In reply to whether the state, territorial or provincial control was effectual, only two stated that it would be considered satisfactory in their respective jurisdictions. (3) Municipal Control. In response to the question of what attempt was made by municipalities to control the pasteurization of market milk, twenty- five replied that certain municipalities in their state or province were exert- ing control, while eighteen stated that no attempt was made to: maintain any supervision. Information obtained on the control of milk pasteurization di- rectly from twenty-one of the largest cities in the United States showed that nine had milk ordinances, three were governed by state laws, and nine did not have any legal authority. The method of supervising pasteurized milk in the cities having legal author- ity consisted of inspection of the pas- teurization plants at various intervals and the examination of samples of milk. In one instance, the city ordi- \ PASTEURIZATION OF MILK 3 nance required the approval of plans on the building or that part of the building intended for pasteurizing milk or cream. The city ordinances cover- ing pasteurization varied in practically every detail. This was especially noticeable in regard to the tempera- ture and holding period required for pasteurization by the holding method. The temperature requirements ranged from a minimum of 140 degrees F. to a maximum of 165 degrees F., the holding period from 20 to 30 minutes, and the temperature to which the milk should be cooled after holding from 45 to 50 degrees F. (4) Definitions of Pasteurization. A questionnaire was sent to four depart- ments of the United States Govern- ment and to every state board or de- partment of health in the United States asking whether they had officially de- fined the pasteurization of milk. Three of the Federal departments replied that their departments had officially defined pasteurization and’ furnished definitions covering the process. Each department defined the holding method of pasteurization. All of the defini- tions differed as to the wording of the temperature and time requirements which made them substantially at variance when applied to the control of the process. Thirty-seven states ‘replied to the questionnaire, and of this number ten reported that pasteuriza- tion had been defined in their respect- ive states. An analysis of these defi- nitions showed that only two states had nearly uniform definitions while the others varied as to temperature and time requirements. It is apparent from the foregoing statements that there is very little uniformity in the Federal and the state definitions of pasteurization in this country. (5) Apparent Lack of Control and Uniformity of Methods. It appears from the information obtained on the state and municipal control of pasteur- a ization plants, that in general there is very evident lack of supervision from a health point of view. There are some instances where it would appear that active steps are taken towards control, but in many cases, through lack of legal authority, appropriations, or organization, the work is not satis- factorily carried out. In state work there are a number of instances where there is an apparent lack of co-ordina- tion of the activities that make pos- sible the proper supervision of pas- teurization while in many others the public health aspect of the problem has not been given any consideration. The lack of uniformity in the defini- tions of pasteurization throughout the United States leads to needless confu- sion and controversy which could be obviated by establishing a definite standard. (6) Absence of Public Understand- ing of Pasteurization. There is quite an evident lack of understanding on the part of the public regarding the ac- tual meaning of pasteurization at the present time. Investigations, in one state, where an intensive survey of milk pasteurization has been under- taken during the past year, show that many health authorities are generally accepting any kind of heat treatment as a satisfactory health measure, while in many of these instances the process is being carried on to prevent the souring of the milk and for advertis- ing purposes rather than to improve the sanitary quality of the milk. There is a very obvious need for an educa- tional campaign to enlighten the pub- lic on the meaning of milk pasteuriza- tion. III. The Effect of Pasteurization on the Composition of Milk. In the early days of pasteurization, disagreement prevailed among those conversant with the subject, regard- ing the effect of heat on the various 4 THE AMERICAN substances which are present in milk, and also on the value of pasteurized milk as a food for infants. The dis- agreement resulted in a very extensive study of the subject by an eminent chemist who established more or less permanently certain points. (1) Effect of Heat on Milk. The chemical changes produced in milk solids by heating at different temper- atures for varying lengths of time were determined. North published in 1911 a summary of the literature on the subject, together with considerable new work done in his laboratory. This summary appeared in the form of a set of curves, which showed graphically the effect of heating milk on the chem- ical composition of its constituents. This diagram was accepted by the Commission on milk standards of the New York Milk Committee and was published by them in their first and second reports.* It points out that the inorganic solids in milk are very little changed by heating to 169 de- grees F. for 40 minutes or less; that the albumen is much more sensitive ‘than the salts, but will resist a tem- perature of 148 degrees F. for 40 min- utes; that the enzymes are the most easily destroyed constituents of the milk, but are still effective after the milk has been heated to 145 degrees F. for 30 minutes The physical condi- tion of the cream is the most sensitive indicator of over-heating, and the cream line is destroyed before any of the milk solids are chemically affected. In brief, the ordinary temperature and time of heating used in commercial pasteurization, namely, 145 degrees F for from 20 to 30 minutes, seemingly has little, if any, effect on the compo- sition of the milk so far as we are able to determine by chemical analyses. (2) Infant Feeding Experiments. (1) Reports of Commission on Milk Standards ap- ointed by the New York Milk Commiftee. Public Health Reports, Vol. XXVII, No. 19. and Vol. XXVITT, No. 34, August 22, 1918. Pustic Herarttu ASSOCIATION The results of these chemical tests did not satisfy many of the medical pro- fession, who were familiar with infant feeding. They still claimed that pas- teurized milk did not produce the same effect on some infants as did clean raw milk. This criticism of pasteurized milk was, to a great extent, tempora- rily quieted by the experience gathered from the immense feeding experiments conducted by the New York Milk Committee in its infant feeding sta- tions, and by similar work done at milk dispensaries in Washington. The results of these experiments seemed very conclusive. Thousands of chil- dren were fed pasteurized milk daily for three years at the New York sta- tions, and the average daily increase in weight of the babies thus fed was equal to the average increase in weight of the babies of like age fed clean raw milk, and no cases of rickets or scurvy developed. The one objection to this evidence seems to be that these children were not always under ob- servation of the station nurses, and other foods may have been given them, which in some way might coun- teract the effect of the heated milk. Within the last few years the con- troversy has been again reopened and much more definite data has been pre- sented. It has been shown that prop- er food substances contain exceedingly small amounts of compounds which are absolutely necessary for the main- tenance of healthy life. These essen- tial compounds have been styled vita- mines. There are several classes of vitamines. One class is responsible for the growth of organisms, and when absent from the diet of the young, growth is not normal. Another class is absolutely essential for the mainte- nance of ordinary metabolism, and without which deficiency diseases such as scurvy and rickets develop. Any process which breaks up or destroys either of these compounds in an arti- ¢ PASTEURIZATION OF cle of food should be avoided. These vitamines have not been definitely iso- lated from foods, and little is known off them in a pure state. Their presence or absence can only be determined in a food substance by its effect on ani- mals, when used exclusively as a food by them. Experiments have been conducted by a number of scientists to determine the effect of heat on the vitamines con- tained in milk. It has been shown that the growth producing vitamine occurs in the butter fat.* It is very resistant to heat, and is not affected by ordinary pasteurization. The antiscor- butic substance is much less resistant to heat. For this reason its properties have been carefully studied. The best known work along this line was done by Hess in New York.** Since 1912, he has had a considerable number of cases of scurvy develop in infants be- ing fed on pasteurized milk in an in- stitution where the diet could be ab- solutely regulated. At first milk was used which was pasteurized in the hos- pital at a temperature of 165 degrees F. for 20 minutes. ‘During the past year, however, pasteurized milk which has been heated to 145 degrees F. for 20 minutes at the plant of a New York dealer was used. Several children de- veloped mild but recognizable cases of scurvy on this diet, while others in the same ward, fed on an identical diet, did not contract the disease. Raw milk was then substituted for the pasteur- ized, all other conditions remaining the same, and in two weeks the scor- butic symptoms wholly disappeared. Hess, therefore, concludes that pas- teurized milk plays an important role in the production of the disease, but is *McCollum, E. r the Isolation of the Substance in Butter Fat_ which Exerts a Stimulating Influence on Growth.’ Journal Biol. Chemistry, Vol. 19, p. 245. **Hess, A. V., Infantile Scurvy. The Blood, the Bloodvessels and the Diet. Am. Jour. of Diseases of Children, Vol. VIII, Dec. 1914, pp. 886-405. Hess, A. F, Subacute and Latent Infantile Scurvy. Jour. A. M. A., Vol. LXVIII, Jan. 27, 1917, pp. 235-239. V., and Davis, M. “Observation on MILK 5 not the sole factor. There seems to be a sufficient amount of antiscorbutic substance in cow’s milk to prevent the development of infantile scurvy, but _this substance is destroyed to such an extent by pasteurization that it is not safe to feed an infant, solely, a diet of pasteurized milk. This discovery need work no practical hardship and should not be used as an argument against pasteurization. An ounce or two of fresh orange juice or potato water given daily entirely eliminates all chance of contracting the disease for these substances contain the vitamine in considerable quantities. Some such substance should be given, however, to an infant fed on pasteurized milk. Work of a similar nature* has been done by feeding small animals, such as guinea pigs, a pasteurized milk diet. It was found that such animals soon died. Control pigs fed on raw cow’s milk likewise were unable to exist. This work, although much discussed and rather generally used as an argu- ment against pasteurization, is of little value. ready known fact that guinea pigs can- not exist on any form of cow’s milk alone. This work is cited simply to emphasize the fact that feeding expe- riments conducted on children consti- tutes the only reliable source of infor- mation regarding the suitability of any particular diet for infant feeding. (3) Infant Feeding vs. Communi- cable Disease. Hess’ work should not be interpreted in any way as an argu- ment against pasteurization. Parker** summarizes the situation well when he says: “It is now recognized that in our large cities it is not feasible to bring the whole milk supply up to the standard of thaf required for infant feeding. The procuring of a supply *Moore, J. J., Jackson, L., Exp. Scurvy Produced in Guinea-pigs by Milk and Milk Products, Vol. LXNVII, Dec. 28, 1916, p. 1981. **Parker, H. N., City Milk Supply, p. 282. It only substantiates the al-. 6 THE AMERICAN of babies milk is a special problem of city milk supply, and this should be remembered in relation to pasteuriza- tion. Pasteurization protects babies from diarrheal diseases, typhoid fever, diphtheria, scarlet fever, and from bo- vine tuberculosis and if, in the opinion of some physicians, this advantage is outweighed by other considerations, or at least in some cases makes the use of raw milk advisable, it does not fol- low that for these reasons older chil- dren and adults should surrender the protection from communicable diseases that the use of pasteurized milk af- fords.” IV. Tue Process or Mirx Pasteurt- ZATION, The Committee questions whether this is the place to undertake the pres- entation of the origin and development of the heating proceses which have re- sulted in the adoption of the modern systems of the practical pasteuriza- tion of milk. It does not consider it necesary to refer extensively to the entire series of laboratory studies re- sulting in the expression of opinions on the destructive action of heating upon cultures of pathogenic bacteria or their thermal death-points. (1) Holding System Required. The Committee feels that it has been suffi- ciently demonstrated that the so-called “holding” system of pasteurization of milk intended for prompt consumption in the fresh state is so much superior to any other type of method as to war- rant the limiting of its activities to that general system. There are prac- tically two stages or operations in every form of application of the “hold- ing” system, i. e., the heating and the holding. This applies whether the milk is heated in one apparatus and held in another, or is heated and held in the same tank, coil, or bottle. The process of pasteurizing milk consists of four essential parts: (a) Pusric Heartir ASSOCIATION the temperature to which the milk must be raised, (b) the length of the time period for which the milk must be held above the minimum tempera- ture, (c) the time in which the milk must be cooled after the boiling pe- riod, and (d) the temperature to which the milk must be cooled. To the temperature and time re- quired must be added either tempera- ture or time, or both, as a factor of safety against irregular functioning of the apparatus used to pasteurize the milk. Some types of apparatus re- quire a far greater factor of safety than others. Regardless of the means em- ployed to apply the pasteurizing treat- ment to the milk, each and every drop of milk must be raised to or above the minimum temperature. The holding time must be as long or longer than the minimum time fixed for the hold- ing period. No averaging of temper- ature or of the holding time can be permitted—that is, if some of the milk is heated to a higher temperature, the remainder must not be ,heated to a lower temperature, or if some of the milk is held beyond the holding time the remainder must not be held for a shorter time. (2) Pasteurization Process Defined. As the pasteurization of milk is a pub- lic health measure, that determination of time and temperature which insures the greatest protection from any possi- ble pathogenic infection is the standard to be fixed for milk for public con- sumption. The Committee believes that the process of pasteurizing milk for human consumption should consist of subjecting the milk to a temperature not lower than 145 degrees F. for not less than 30 minutes. It feels that the scientific evidence already presented from studies on the process of pas- teurization justifies the requirements above stated for pasteurized milk, and that by fixing only a minimum temper- ature and time, sufficient latitude is ( PP PASTEURIZATION oF MILK 7 allowed for any fluctuation above the minimum points that may be required in commercial practice. There are many other factors other than temper- ature and time requirements that enter into the problem of the efficient pas- teurization of milk which are discussed under other subjects in this report. V. Tue MEcHANICAL FEATURES AND THE OPERATION OF PASTEURIZ- ING PLANTS. The material included under this subject is limited to pasteurizing ap- paratus and its operation; the matter of the building, and of can fillers and cans, bottle fillers and bottles, can washers, bottle washers, sterilizers, cap sterilizers, bottle inspection, cap storage, etc., forming important parts of milk pasteurization, are not consid- ered. Owing to the wide range of ca- pacities and importance of local condi- tions, it is impossible to make any specific lay-out that would apply to even a majority of pasteurizing plants. There are, however, certain general conditions that apply to all plants and all plant operation, to all pasteurizing apparatus and the machinery co-ordi- nating therewith, to the sterilization of containers, to the treatment of the milk, and to the handling of the milk after treatment, in order that the out- put of the plant may be entitled to be sold under the marking or label of “PASTEURIZED.” (1) Methods of Pasteurization. Milk may be pastuerized in the bottle or have the treatment applied by means of apparatus, which may be of what is known as the batch or inter- mittent type, or as the open or closed continuous type. The apparatus gen- erally used for applying the pasteuriza- tion treatment is either of the vat type, that is, (a) a vat in which the milk is heated, held and cooled, or (b) a combination of a heater, a vat of series of vats for holding the milk static and a cooler, or (c) a combina- tion of a heater, a series of vats for holding the milk flowing and a cooler, In any of the above mentioned types of apparatus the treatment may be ap- plied, and pasteurization effected by a competent operator, providing the ap- paratus is free from inherently danger- ous defects. It is entirely practical. to construct the intermittent or continuous type of pasteurizing apparatus so that every drop of milk and every particle of foam developed by the movement of the milk will have passed through the complete course of the apparatus, and that when milk is supplied to such an apparatus at the proper volume per time period, and the necessary tem- perature maintained, the milk delivered from the discharge outlet will have had pasteurizing treatment. (2) Pasteurization in the Bottle. Milk that is pasteurized in the bottle must have the full minimum treatment applied, and care must be used in tak- ing the milk temperature so that the instrument is not affected by the hot milk at the top of the bottle, or by the heating medium. The time of the holding period does not start until all of the milk in all the bottles is at the minimum temperature. This temper- ature must not be lowered until the end of the holding period, and the hold- ing period must not be shortened. If any temperature recording instrument is used, care must be taken to see that the heat of the apparatus does not cause a higher reading than the actual temperature of the milk. If water is used in cooling, care must be taken to prevent it from being drawn into the bottle by the contraction of the milk. Bottles used for milk to be treated therein must be washed and sterilized before being filled with milk, as the pasteurizing temperature is not suffh- cient to sterilize the bottles that have been returned to a milk plant, often 8 THE from dumps and rubbish heaps, and frequently containing very objection- able and highly dangerous material. (3) Pasteurization with Intermit- tent and Continuous Flow Apparatus. Regeneration in a pastcurizer is an ¢x- change of temperatures between the hot and the cold milk, and is obtained by an apparatus that either brings the flow of hot and cold milk on either side of the metal surface whereby the hot milk is cooled by the cold milk and the cold milk is heated by the hot milk, or by an apparatus that circulates water first through the cooler, which becomes heated by taking up the heat of the hot milk. This water, after the addition of the steam required to bring it up to a temperature necessary to heat the milk, is circulated through the heater and raises the milk to the pasteurizing temperature. The eco- nomic advantage of regeneration is ap- parent, when it is considered that water at 38 degrees F. may be run into a cooler and be discharged from the cooler at 120 degrees F., all the steam then required to heat the milk is that necessary to raise this water from 120 degrees to 150 degrees, at which tem- perature the water will heat the milk to 145 degrees. ,To accomplish this it is necessary to have properly con- structed and proportioned apparatus. This system is of advantage only in milk plants that have a run of several hours’ duration. If milk is being held in the holders for thirty minutes for the first half hour of the run, there is no milk to cool, and on the last half AMERICAN PUBLIC ~ of the run, there is no milk to heat. Regeneration is an economic advan- tage only, and of no advantage to the milk. It is a decided disadvantage, when the apparatus is so constructed, that the milk is forced through an ex- tra device that has gasketed closures or troublesome cleaning features. Ap- paratus in which any possible mixing by leaks or seepage between the hot HeALTH ASSOCIATION milk and the cold milk in the milk channels of the apparatus is improper in construction and may destroy the effects of pasteurization. In a continuous flow pasteurizing ap- paratus, it is important to have the supply of milk flow to the heater at a uniform predetermined rate per hour, proportionate to the capacity of the apparatus, in order to maintain the holding time, the heating temperature and the cooling in co-ordination with uniform flows of the heating and cool- ing mediums. This uniform supply flow cannot be properly maintained by a pump, for, owing to the variations in slippage and varying quantity of air in the milk, a pump will not always dis- charge the same amount of milk when running at the same rate of speed. (a) Flow Controllers. A device termed a “flow controller,” consisting of a small metal tank about thirty inches in diameter by twelve inches deep, with the milk supply pipe pro- jected through the side and having a float to maintain a constant depth ‘ot milk in the tank and a fixed outlet of proper area to discharge the amount of milk wanted per hour, will maintain a constant flow when the supply is suf- ficient. The fixed outlet must dis- charge into an open connection to pre- vent syphonage. In the pasteurizing installation the “flow controller” is placed above the heater to which the milk flows by gravity. (b) Heaters. It is important to have the heater for the milk contain the necessary heating surface to raise the temperature of the milk to 145 degrees F., when running at full capacity and using water not more than five or six degrees higher as the heating medium. With such a heater, overheating can- not take place when the temperature of the water is properly controlled, even if the flow of the milk is reduced for a time, as is often the case in plant operation, A heater with a relatively PASTEURIZATION OF MILK 9 small surface in proportion to the ca- pacity claimed for it must utilize a heating medium of much higher tem- perature in order to heat this quantity of milk. While such a heater will dis- charge milk of apparent uniform tem- perature, it is actually only an aver- aging temperature and the cream of that part of the milk that is over- heated will not raise in the bottle. When possible, the heater should be installed above the holding tanks, so that the milk may flow by gravity. Milk heaters should have, if any, as few joints or loose parts as possible, for joints and unions are likely to leak and cause loss of milk. A deposit from the milk forms on the heating surface that must be removed every day: there- fore. the use of a device for heating milk that cannot be scrubbed clean should be prohibited. The instrument for controlling the temperature of the milk discharged from the heater and the instrument for recording the same are hereinafter re- ferred to. (c) Holders. The reliable opera- tion of the holding device of the pas- teurizing apparatus is most important if efficient treatment is to be obtained. In the systems using a vat or series of vats in which the milk stands dur- ing the holding period, a part of the milk may be held much longer than the holding period; while this is no disad- vantage, it is a condition often over- looked. The foam on the top of the milk in the tank may’ lower in tem- perature, or the draw-off valves may leak and allow seepage. of the not: fully heated milk. If the heating sur- face of these vats is supplemented by coils, these coils are troublesome to clean, and if the coils rotate, stuffing boxes are inevitable. In the vat sys- tem it is important to have either suf- ficient insulation of the heat main- tained by circulation of controlled tem- perature water, to prevent the lower- ing of the temperature of the milk and the foam. It is also necessary to have a safety outlet in the discharge pipe from the vats that will permit any milk that may leak through the valve before the end of the holding period to run out onto the floor. In the system using a series of hold- ing tanks for continuous operation, there should not be less than three tanks to the series and set vertically. They must be insulated except when provided with controlled temperature water jackets. One and _ one-half inches of well-packed hair felt between metal castings is sufficient insulation. These tanks must be provided with a teeder that will distribute the inflow- ing milk into small streams at right angles to the vertical flow of the milk in the tank and a collector for the out- going milk that will collect the milk through several orifices. The milk from the heater is supplied to the first tank of the series, from the first tank to the second, and so on throughout the whole series. The milk content of the series of continuous flow holders should be the same as the maximum hour capacity of the heater; this will give with 50% efficiency a net holding time of thirty minutes. A theoretical holding pe- riod of one hour, and with an efficiency of 75%, will give a net holding time of forty-five minutes, an excess holding of 50%, or fifteen minutes over the mini- mum holding time of thirty minutes. An excess holding time only requires an increase in the size of the tanks, which adds but little to the original cost and the additional cleaning is very small, with no extra cost for op- eration. This excess holding time over the thirty minutes’ minimum is a fac- tor of safety in pasteurization that may well justify its general adoption on all The drain outlet from the bottom of the continuous flow holders must not be connected directly to the pipe lead- . 10 THE AMERICAN ing to the cooler, but should be con. nected to a “flow controller” same as hereinbefore described that will not permit the milk being drawn off at a more rapid rate than the rate of fill- ing. This “flow controller” must not have a connection with the cooler dur- ing the continuous operation, so that in case any of the valves in the dis- charge of the holding tanks should leak, which is likely to happen at any time, the milk that is seeping through would not pass to the cooler and infect the finished product. After the con- tinuous operation of the milk flowing direct from the holding tanks to the cooler is finished, the ‘flow contrviier” at the discharge of the holding tanks is connected to the cooler and the milk drawn off. The temperature recording instru- ment in the discharge of the continu- ous flow holding tanks records the temperature of the held milk, which must be at or above the minimum holding temperature, and also shows the time of drawing off the tanks by the interruption of the continuous flow. Continuous flow holding tanks have no moving parts or moving valves, stuffing boxes or coils, or pipe fittings, or connections under pressure; they are easily cleaned and sterilized. (d) Coolers. The cooler for cool- ing milk, after the holding period, forming a part of either the intermit- tent or continuous types of pasteuriz- ing apparatus should have the neces- sary cooling surface to cool the vol- ume of milk per hour to within two or three degrees of the temperature of the water circulated for cooling. It is preferable to use water for cooling in- stead of low temperature brine or di- rect expansion of ammonia. With the brine or direct expansion ammonia, it is almost impossible to prevent a part of the milk from being frozen. The water for the cooler may be cooled by Pusitic HraLttru ASSOCIATION direct expansion, or by low tempera- ture brine. In a continuous pasteurizing appar- atus, milk heaters and coolers, when properly constructed and proportioned in relation to the quantity of milk to be heated per hour, require the volume of water circulated to exceed the vol- ume of milk by about 5 per cent. The circulating water cooled from a normal temperature to 38 degrees F. will cool the milk at approximately 42 degrees F., and with milk from the holder at 145 degrees F., the circulating water will leave the cooler at 120 degrees to 125 degrees F., obtaining all the ad- vantages of regeneration. This water, when passed through a water heater, using either exhaust or live steam, or both, must be raised to about 149 de- grees to 150 degrees F., which will, when circulated through the heater, heat the milk to 145 degrees F. This water, when discharged from the heater, can be run to the water storage tank of the building and used for gen- eral purposes. Sterilization of the cooler is neces- sary, and the cooler must be constructed to stand this process. To accom- plish sterilizaticn, steam at 10 pounds pressure should be turned into the in- side of the cooler and the apparatus maintained under these conditions for the time necessary to produce steriliza- tion as determined on the condensa- tion water drips from the bottom of the cooler. In an open surface cooler, the steam is turned into the water thoroughfares after emptying, and maintained under these conditions for from one to two hours. The stress on a cooler caused by sterilization comes more from uneven expansion than from pressure and a steam pressure of 10 pounds is ample. It is difficult to sterilize a cooler not constructed to withstand the application of this amount of pressure, and the best way of accomplishing what can be done in PASTEURIZATION OF MILK the sterilization of such a cooler is to flow boiling water down over it; even the expansion caused by this heat may buckle the surface and prevent proper sterilization. The sterility of a cooler can be determined by flowing sterile water over it after the cooler has been allowed to cool. All open surface coolers should have removable metal covers to protect the milk, or should be installed in a prop- erly constructed room that is not used tor any other purpose. Milk should be fed to open surface coolers through a perforated pipe that does not permit foam to gather, as the collection of foam is often favorable to large bac- teria growths. From the cooler the milk flows to a cold milk tank of relative small dimen- sions that has an agitator to keep the cream from raising. It is not necessary to insulate this tank under usual con- ditions. From this tank the milk flows to the can filler and the cans, and to the bottle filler and the bottles. (e) Pumps. Milk pumps should be eliminated from milk plants wherever possible ; where their use is necessary it is preferable to use a pump large enough to handle the milk at a moder- ate speed. As the pump must come apart every day for cleaning, pumps with few parts that are accessible for cleaning and are put together with strong bolts, are the best type. The stuffing boxes on either the piston or rotary type pump must be opened up, cleaned and packed with clean packing every day. Off flavors in the milk are sometimes caused by the putrid milk that accumulates in the stuffing box, corrodes the metal and seeps into the milk. Milk pumps should not be installed to pump milk after it has been heated if this can possibly be avoided, since this practice increases the liability of contamination. (f) Stuffing Boxes. Stuffing boxes 11 in vats, tanks or other apparatus are to be avoided wherever possible, and if used, must be cleaned and packed clean every day. If not kept in first class order, they are likely to cause corrosion and off flavors in the milk. g) Fittings and Valves. All ma- chinery, apparatus, pipes and pipe fit- tings, and valves used for pasteurizing milk, must be so constructed as to permit every part with which the milk comes in contact of being opened up and scrubbed with a brush. There must be no cracks, crevices or inac- cessible corners, nor must there be any absorbent or spongy material used in construction. Gaskéts should be elim- inated, but if they are necessary in some types of apparatus, heavy paper gaskets should be used and renewed daily. (h) Metals Used in Construction ef Apparatus. Apparatus constructed of copper, tinned and with tinned bronze castings, has given satisfaction in many plants, both before and after the tin has worn off. Tinned copper pipe, and red brass fittings for milk cocks, have given satisfactory service. Any metals, alloys or combination of metals that produce electric action when subjected to the condition of a milk plant should be avoided, as the decomposed metal may cause off fla- vors in the milk. (i) Temperature Control Appar- atus. Temperature control of heating the milk for pasteurization may be ob- tained by using the well known and practical temperature controllers on the market; the sensitive part of the instrument is preferable placed in the water circulation to the milk heater, when a suitable type of heater is used, or it may be placed in the hot milk dis- charged from the heater. In all cases small valves in the steam line should be used, as their opening and closing does not cause such fluctuation in tem- perature. In almost all cases steam 12 THE AmeEricAN Pubptic HEALTH ASSOCIATION 1s required all the time so that a by- pass should be used and nearly enough steam allowed to pass through this by- pass valve to maintain temperature. The controller will then only have to act on the additional steam required, and may be comparatively small, and when closed does not cut off all steam from the heater. All temperature controllers must have a constant steam pressure to op- erate properly; therefore, it is impor- tant to use at least one efficient steam pressure valve between the boiler and the controller instrument. In many cases where there is a large fluctuation in the boiler steam pressure, two re- ducers can be used to advantage in ob- taining a final constant pressure for the controller. (j) Temperature Recording Instru- ments and the Interpretation of Re- cording Charts. The only means that the operator of a pasteurizing plant or the health authorities have of knowing the treatment to which the milk has been subjected, excepting by constant testing with the thermometer, are the chart records made by reliable time and temperature recording instru- ments, that have their bulbs placed in such-a manner that the bulb is not in- fluenced by the temperature of the ap- paratus. Instruments sensitive to the changes of temperature and quick to record such changes should be used in- stead of sluggish instruments. All in- struments should have pins close to the center post that holds the charts from inadvertently rotating, or from being intentionally rotated by hand to produce fake records. Temperature recording instruments are not thermometers; they record temperatures after being adjusted to correspond with a thermometer, and require frequent testing to assure cor- rect records. The operator in personal charge of each pasteurizing apparatus should have a calibrated thermometer and should be held responsible for the cor- rectness of the recording instruments and of the charts. Each chart should have printed on it a statement certify- ing to the correctness of the chart, to be signed by the operator, with a place for date and identification mark of the apparatus of which chart is the record. On the chart of the holding tanks there should be a statement to the effect that the pump speed (if a pump is used) has not been accelerated during the run, and that the holding time has not been shortened. - The op- erators should be held to rigid account for the correctness of the charts on which they have signed the certifica- tions. All charts for recording the time and temperature of milk treatment must be set on the instrument dial at a uniform time so that the time elapsed from one treatment to another can be checked and determined. All the charts must show the time of the operation from start to finish. The chart showing the temperature record of the milk in an apparatus where the milk is heated, held and cooled in a vat, must show the time, the temperature of the milk when it starts to raise, the time when the milk reaches its high point, the temperature maintained during the holding period, the time when the cooling temperature commences, and the temperature to which the milk is cooled. If the milk . is cooled by a separate cooler, the chart on the cooler will record the cold milk temperature, and the end of the: holding period which is indicated on the chart as the time of the start of the cooling operation. The chart showing the heating tem- perature record of the milk in a con- tinuous flow apparatus, must show the time and temperature of the milk when the heater starts to discharge, the tem- perature of the milk as it is discharged PASTEURIZATION OF from the heater throughout the run, and the time of the finish of the dis- charge of milk from the heater. The chart showing the holding time and temperature record of the milk in a continuous flow apparatus, must show the time at which the first milk is dis- charged from the holders, its tempera- ture, the temperature of the milk main- tained through the run, and the time of the finish of the run. The sensitive bulb of the recording instrument must be placed in the continuous flow dis- charge pipe of the holding tanks and not in the pipe through which the milk flows when the tanks are being emp- tied. An apparatus having a series of tanks that are emptied at the end of the run, the interval between the fin- ish of the run and the starting of emp- tying the first tank, must be clearly indicated on the chart recording the temperature of the cold milk; likewise, the interval between emptying the other tanks of the series will also be indicated on the cold milk chart; this is caused by interruptions to the flow of the milk in emptying the holders. It is of the utmost importance to check the temperature of the first milk discharged from the holders, if this milk does not show 145 degrees or over when the milk supplied from the heater was 145 degrees in a properly constructed apparatus, it indicates that the holders were not properly pre- heated before beginning the operation. This underheated milk may defeat effi- cient treatment, as all of the milk dis-~ charged below 145 degrees may carry a seeding with it and infect the subse- quent apparatus through which it flows to the detriment of the milk of proper temperature following it. The charts showing the records of the temperature of the cold milk in a pasteurizing apparatus, must show the time and temperature maintained through the run, the temperature to Mirk 13 which the milk was cooled during the run and the time of the finish of the run. To check up the holding period of a milk run through a continuous flow pasteurizing apparatus from the. chart records, the elapsed time after the time of the discharge of milk from the heater to the holders, and the time of the first discharge of milk from the holders, will be the theoretical holding time. If the flow of milk to the ap- paratus is uniformly maintained throughout the run, the theoretical holding time for the run will be the same; if, however, after the complete apparatus is in operation and the the- oretical holding time is established on the chart record, the pump speed is accelerated or the flow of milk in- creased by any means, the holding time will be shortened, and effective treatment lessened. Therefore, it is of importance to install the pasteuriz- ing apparatus in such a manner that the flow of milk per hour cannot be increased beyond the rated capacity of the apparatus. The time of emptying the holding tanks can be checked by noting the elapsed time between the finish of the continuous flow from the holders, as. shown on the holder chart, and the time of finishing the run of cooling the milk, as shown on the cooler chart. If the holding time of the milk through the run cannot readily be de- termined from the charts for any rea- son, the quantity of milk pasteurized should be taken from the plant rec- ords and the quantity of milk run through per hour determined, comput- ing the time between the starting and finish of the holding operation, deduct from this any time lost owing to in- terruption to the flow (these interrup- tions will appear on the charts) and check the quantity of milk per hour actually run through the apparatus with its rated capacity. 14 Tur AMERICAN Apparatus may be so constructed that it will do efficient pasteurization and the milk develop a satisfactory cream line when the quantity of milk handled does not require the raising of the temperature of the heating medium to more than a few degrees above the temperature to which the milk is to be heated. When more milk than can be properly handled is forced through such an apparatus, the heating medium must be raised in tem- perature to maintain the temperature of the milk, with the result of impair- ing, if not eliminating, the cream line. (k) Cleaning and Sterilizing Appa- ratus. The whole pasteurizing appa- ratus must be thoroughly cleaned every day; nothing but thorough cleaning should be tolerated regard- less of any reasons for careless clean- ing that may be offered. Every par- ticle of grease film must be removed from the apparatus as grease film is very favorable to bacteria growths. Immediately after the finish of the run, the milk should be rinsed off with cold water and every part of the ap- paratus opened up and scrubbed with brushes and cleaning powder. Where, owing to the heat, a deposit from the milk has formed, this deposit must be cleaned off by using an abrasive clean- ing powder, if necessary, and all thor- oughly rinsed, first with cold water then with hot water. Wash sinks preferably of metal, long enough to take the milk pipe and hav- ing drainage racks for rinsing, should be placed conveniently so that all milk pipe, milk fittings, cocks, ete., which must be taken apart at every point every day, can be placed in these sinks and soaked for an hour or so before scrubbing. After each and every part has been scrubbed clean and bright, it must be rinsed with clean cold and then hot water, and the apparatus as- sembled. After the apparatus has been put Pusrtic HeratrH ASSOCIATION together and is ready for operation, it must be sterilized. To sterilize, con- nect the steam supply at 10 pounds pressure to the various parts of the apparatus so that the steam will reach every part, using great care to drip off all water of condensation which would accumulate in any part and pre- vent the steam from heating it up, and also cause uneven expansion produc- ing great strains in the apparatus. If high pressure steam is used for steril- izing, its greater velocity and higher temperature causes much more rapid heating of that part of the apparatus with which it comes in direct contact, and consequently. greater expansion of the metal at that point, setting up physical strain that will reduce the durability of the apparatus. In any part of the apparatus that will not stand pressure, lids should be closed down as tightly as safety permits, so that the steam may be confined as much as possible. Metal pipe or metal hose should be used for sterilizing steam connections to any part of the apparatus with which the milk comes in contact as rubber hose disintegrates and deposits black specks which will appear in the milk. It usually takes from two to three hours to. sterilize completely an ap- paratus with 10 pounds of steam. To determine whether sterilization has been effected, collect samples of the condensation water from the various parts of the apparatus and if bacterio- logical examination shows these to be sterile, the apparatus is in good order. The heater and' cooler should be sterilized after the washing is finished, or long enough before the milk is run to become cool before any cold water is turned into them. The holding tank may be sterilized at the same time as the heater and cooler, but must not be permitted to cool down below the pasteurizing temperature when the milk is run. If, owing to the conven- PASTEURIZATION OF MILK 15 ience of plant operation, these tanks do cool down they must be heated up to the pasteurizing temperature before the milk is allowed to flow in. Chemicals that can be employed as a germicide in milk should not be used as a part of the cleaning of pasteurizing apparatus. The pasteur- izing treatment of milk is a physical treatment of the application of heat to the milk, and in this, chemicals play no part. Chemicals used as a part of this cleaning can be removed only by thorough draining and rinsing, and a careless and inefficient rinsing would leave a residue of chemical in the ap- paratus that may of itself or its cor- rosive action on the metals of the appa- ratus, cause a condition in the milk flowing into it that might have a seri- ous effect on the milk consumer. The use of such chemicals in cleaning pas- teurization apparatus should be pro- hibited. (4) Some Dangerous Defects in Pasteurization Apparatus. Pasteuri- zation apparatus is inherently danger- ous that shows the following defects: (a) That has a milk pipe leading from the bottom of the heating or holding tank or tanks to the cooler, either direct or through a pump that depends on a milk cock in this pipe as a stoppage or safeguard, to prevent the raw milk or the partially heated milk, or heated but not held milk, from flow- ing to the cooler, mixing with and in- fecting the finished product. No milk cock is secure against leaks since a milk cock may be tight for months and may leak through at any time. A bristle of a brush, a thread, a bruise in cleaning, or tneven contraction after expansion, may cause a seepage leak that utterly destroys the efficiency of pasteurization which the apparatus is supposed to effect, and this may hap- pen without the knowledge of the most careful operator. (b) That utilizes a rotating valve having connections from the heater to the holding tanks and to the cooler. With such a valve, abrasion or cutting may occur at any time without the op- erator’s knowledge, which will form a channel between the connections lead- ing to the various tanks that may shorten the holding time. Should a channel in the valve be cut from the holding tank connections to the cooler connection, the heated, but not held milk, will pass directly to the cooler and mix with the finished product. Efficient pasteurizing apparatus can be constructed without using valves or mechanisms with which the milk comes in contact and that require lubrication with vaseline or other kinds of grease. (c) That has a series of tanks for holding the milk through which the milk flows continually, that does not consist of enough tanks to prevent a’ | current from forming and flowing through the whole system, and that does not have in each tank a device to diffuse the inflowing milk and a device to collect the outgoing milk that pre- vents the formation of currents in the milk. All holding systems of this type should have at least three tanks and their net efficiency should be proven by color tests. (d) That has a by-pass pipe from the raw milk tank to the cooler, cut- ting out the heater and the holder, or from the heater to the cooler, cutting out the holder; such a pipe is not nec- essary and might be used as a time saver and is an invitation towards il- legal and dangerous methods. (e) That is connected up to use the same pump to empty the holding de- vice at the end of the run that is used to pump the raw milk. An apparatus that requires a pump to force the raw milk through the heater,. holder and cooler, when set on an approximate level, will leave the holder full of milk at the end of the run. This milk should be pumped through the cooler 16 THE AMERICAN by means of a separate pump. if the raw milk pump is used, it will infect the heated and held milk unless it is washed and sterilized’ during the op- eration. Pasteurizing apparatus should be so installed that all parts will drain through the whole system at the finish of the run, otherwise, the milk left in the apparatus will be neither raw nor pasteurized and must be utilized as a by-product. The public are placed in jeopardy of receiving watered milk when water is used to force the milk out of the apparatus at the finish of the run and such practice should be prohibited. A proper installation of apparatus will obviate this condition. (f) That, in which foam developed by the milk movement, floats on the top of the milk while the milk is stand- ing in the holding device, and owing to the lack of effective insulation of temperature maintenance, the tempera- ture of the foam will drop below the minimum holding temperature, which is the same in result as lowering the milk temperature and defeats efficient treatment. (g) That, on account of pipe connec- tions or other causes, permits any low- ering of the temperature of the milk in transit from the heater to the holder, or lowering of the temperature of any part of the milk while in the holder. (h) That does not have means to prevent the emptying of continuous holders at the finish of the run at a more rapid rate of flow than the rate of filling, thereby shortening the hold- ing time of the milk in the tanks at the finish. (i) That does not have an absolutely safe device in the discharge outlets from the holding tanks to the cooler so that any leakage or seepage through the milk cock in the pipe emptying the holding tank, will flow out onto the floor in view of the operator, so that the leak may be remedied, instead of Pusiic HEALTH ASSOCIATION flowing to the cooler there mixing with and infecting the finished product. (j) That has a steam or motor driven pump, maximum speed of which will force the milk through the holding device at a rate that reduces the hold- ing time of the milk below the min- imum, or a pump in which the rate of flow depends on the judgment of the operator to maintain the proper speed in order not to supply milk to the holding device at such a rate as will reduce the minimum holding time. A pump on account of variations in slip- page and air in the milk does not pro- duce a constant flow at a constant speed. VI. ANALYTICAL CoN TROL OF PASTEURI- ZATION PLANTS. This phase of the report includes a discussion of the physical, chemical or physico-chemical and biological methods and procedure used to determine the effectiveness of the pasteurization processes. (1) Physical Methods. The purely physical or mechanical methods of supervisory control have been consid- ered already but it may be well to men- tion some of the important considera- tions requisite to the adequate testing of the efficiency of time and tempera- ture recording devices. (a) Testing of Time and Tempera- ture Recording Devices. Thermometer tests on recording instruments to show: comparisons at lowest temperature on chart, at highest temperature on chart, at 130 degrees to 160 degrees F.; de- terminations to show rapidity of action to sudden changes of temperature, slight changes of temperature, changes 140 to 155 degrees F.; effects on tem- perature recording by changes in depth of bulb and clock located as follows: bulb low-clock high, clock low-bulb high, bulb and clock level: character- istic of instruments — printed chart lines may be too close, too heavy, in- PASTEURIZATION OF MILK 17 correct charts, revolve eccentrically, not adapted to this form of recording, recording lines may be too heavy, too light, may be blurred, poor paper, poor ink, difficulty of adjustment, easily faked by spinning of chart, by falsely adjusting pen. (2) Chemical Methods. No purely chemical test capable of differentiating between pasteurized and unpasteurized milk have as yet been developed to a satisfactory point and certainly none have been presented which would give results which would warrant any con- clusion that an appropriate heating as to time and degree had or had not been applied. (3) Physico- Chemical Methods. While Frost and others have presented methods for determining by micro- staining reactions whether a given sample of milk has been subjected to a heating process, such procedures have been far from giving results which could be utilized in even estimating the degree of temperature attained or the duration or the thoroughness of its application and yet upon these factors rests the efficiency of all pasteurization processes. (4) Biological Methods. In any sys- tem designed to measure accurately the effectiveness of the pasteurization proc- ess, the main and special object of the elimination of disease-producing para- sites as distinguished from the reduc- tion in numbers of bacteria must al- ways be kept to the front. Failures to give proper relative values to these two results occur commonly by reason of the past general utilization of the count of the total number of bacteria in a cubic centimeter of a raw milk as an adequate measure of the sanitary quality of that product. However, the almost insuperable difficulties sur- rounding any attempt at testing a practical system by the use of milk ac- tually innoculated with pathogenic bacteria, has left the investigators in a degree of uncertainty with no choice but to interpret the results of approp- riate tests on the forms of bacteria commonly found in milk in the light of the probable effects on those having the power of producing disease in man. The usual biological determinations aim, therefore, at the demonstration of the direct and indirect effects on the degree, duration, and thoroughness, of the heating and cooling operations upon the bacterial flora of the raw product. In view of the relatively large amounts of milk handled even in the very shortest operative runs of even the smallest forms of practical pasteur- ization systems, it is obvious that sub- stantially all control observations must be made while the system is in prac- tical use—that is, the demonstrations of efficiency involving tests of the product, must be made upon the milk as it comes to the plant in the regular course of business, although this tends to introduce a considerable number of variable factors by reason of the .mul- tiplicity of experiences and vicissitudes through which the raw milk may have passed which may have affected its bacterial flora. (a) Biological Demonstrations of Efficiency, Procedure A. A. Comparison made between the counts of viable bacteria in the raw and the pasteurized and cooled milks, sup- plemented by similar bacterial counts at various important intermediary stages. These comparisons are frequently expressed in terms of percentage re- ductions in numbers of living, i. e., viable bacteria on the usual culture media. Ayers and others have called atten- tion to some of the fallacies involved in the use of this system of percentage reduction in numbers of living bac- teria, as a means of judging the effi- 18 THe AMERICAN Pustic HEALTH ASSOCIATION ciencies of the design and operation of heating or pasteurizing processes. Bacterial Flora in Raw Milk. The floras of raw milk are obviously sub- ject to extensive variations as to ori- gin, character and condition of the bac- teria and of the effects of the growth or other activities of the same on each other and on the product itself. | The bacterial flora of a milk about to be pasteurized is derived from many sources, i. e., from the cow, i. e., milk ducts and reservoirs, udder, hair, skin, feces, saliva, etc., and from the subse- quent growth of the same if any in the milk; from the human beings handling and milking the cows, i. e., skin, urine, feces, saliva, etc., and from the subse- quent growth if any of the same in the milk; from the surroundings of the cow and human attendants, i. e., hay, grains and other feeds, soil, water, air, etc., and from the subsequent growth if any of the same in the milk; from flies, insects and other animal contamina- tions and from the subsequent growth of them in the product; from the farm utensils with which the milk on pre- vious occasions has come in contact, the flora on the surface of which may be the result of failures in proper cleaning and are, therefore, of origins already mentioned, with or without subsequent growth due to bacterial in- cubation on moist apparatus surfaces or in cracks and crevices; or they may be due to the direct contamination of the milk handling apparatus from any or all of these sources of milk pollu- tion just mentioned and from the incu- bation of these added micro-organisms on the moist and greasy surfaces of the utensils, cans, etc. Factors Causing Changes in Bac- terial Flora. The combined floras from these various sources may have been greatly modified by the time the product reaches the pasteurization sys- tem by action of bacterial antagonisms or associated growths, the character of which may have been subject to change by the likely alterations in tempera- tures, by agitations and other physical states to which milk in transit is con- tinually exposed. These may likewise be influenced by the character of the metallic surfaces with which the milk has been in contact, such as brass, cop- per, and inappropriate metallic combi- nations. Chemical Treatment of Milk. There occur frequently outbreaks of effort to keep down the bacterial counts in raw milk by various chemical treatment of milk and of milk handling apparatus. Those in which the germicide or pres- ervatives have been added directly to the product itself have been but short lived. They are not often indulged in at present. Those in which the germi- cides are utilized in the sterilization or prevention of bacterial incubation in certain forms of milk handling appa- ratus, such as rubber milking machine parts, are not objectionable when the product used is harmless and special care is taken to remove the germ killing or restraining solutions by thorough rins- ing. Where this rinsing is not done the solution may gain direct access to the milk subsequently handled in the apparatus. As the use of such solu- tions is extended to the washing or sterilization of pails, cans, etc., fairly substantial amounts of even more than one solution each having its own sep- arate chemical characteristics, may finally find their way into the raw product. Here we must consider the probable selective germicidal effect upon different types of bacteria and other micro-organisms which, if some subsequent incubation occurs, is very likely to upset that important and more or less normal “balance” between thé numbers of acid producing, inert, and alkali developing groups of bacteria. Any procedures liable to suppress or eleminate the natural preponderance of the non-spore forming acid types PASTEURIZATION OF MILK 19 without seriously affecting those al- kali producing species which develop spores, will be liable to cause serious conditions in the raw milks presented for pasteurization. Action of Heat on Different Bac- teria. It is well known that exceed- ingly wide variations in susceptibility to the destructive action of heat exists among the different species, groups and strains of bacteria and between individual numbers of the same. resulting from the growth of these variable biological agents have more or less selective destructive action upon each other, especially when tempera- tures approximating their thermal death points are applied. Under such conditions the utilization for estima- tions of pasteurization efficiency of any numerical system, such as a percent- age of the bacteria in the raw milk killed by the process, gives results in which the implied accuracy of the means of expression of the results is apt to be entirely fictitious. The use of percentage reductions in numbers of living bacteria as a measure of effi- ciency of pasteurization is not to be recommended. Interpretation of Results. It is evi- dent that the results of the operations of all of those very variable factors in the production, handling and transpor- tation of milk, up to the time of its in- troduction into the pasteurization sys- tem are impossible of adequate detec- tion by any simple laboratory or other technical procedure and that they are not easy of estimation even if one has a reasonably correct and detailed his- tory, of the product. ' To those very familiar with the re- sults of bacterial investigations of pas- teurization apparatus and who also are experienced in biological problems in milk production and handling, in pas- teurization processes, the results of bacterial counts of the raw and pas- It is also well known that different products ° teurized products and of sample col- lected at important intermediary stages in the process, are of considerable value, although they are of more sub- stantial utility when they can be corre- lated with the more or less detailed history of the product including the conditions to which it has been sub- jected prior to pasteurization. There- fore, in every investigation, having as its object the determination ‘of the effi- ciency of a pasteurization system, one of the most essential features consists in the collection of a well-planned ser- ies of samples for the determinations of total bacterial counts, by use of the methods recommended by the Committee on Standard Methods of the Laboratory Section of this Asso- ciation for the bacteriological examina- tion of milk for legal purposes, i. e., those of the greatest degree of accu- racy. However, in the interpretation of the results of such studies, those of adequate training and experience in this and allied fields will always give due consideration to the information available regarding the history of the product subjected to the pasteuriza- tion process. (b) Biological Demonstrations of Efficiency, Procedure B. B. Another procedure considers the final total numbers of living bacteria at some stage in the history of the milk subsequent to its pasteurization, as a measure of efficiency of the pas- teurization system. This plan is obviously better adapted to the estimation of the general bac- terial condition or quality of the prod- uct itself than it is useful in the de- termination of the pasteurization effi- ciency. It consists essentially in ac- cepting the results of one, i. e., the final step in the performance of a rather elaborate study, as adequately repre- senting the results of the entire inves- tigation. As generally used it compli- cates the study of the vital question of 20 THe AMERICAN the real effect of the heating process by introducing the results of the action of the various other factors which have altered the character of the product itself. It is true that the character of the raw product influences greatly the results of the study of the heating process, but the final results alone give at best only clues as to causes pro- ducing them. For example, a very low count milk could be passed through a bacterially clean, but other- wise very poorly designed or operated pasteurization system and yet yield a’ total count, which if taken alone might be acclaimed as indicative of high pas- teurization efficiency. On the other hand, a high count milk might have been passed through a modern, well designed and efficiently operated pas- teurizing plant and have given the same results. Still further those who make use of the final total counts as indicative of pasteurization efficiency or the lack of it, fail to consider the fact that some of the most common sources of high bacterial counts in pas- teurized milk have no relation what- ever to the efficiency of the heating processes applied or the thoroughness of their application, but are essentially matters of the adequacy of the previous cleaning of the cooling and bottling systems through which the product has passed after heating. Interpretations of Results. As a means of estimating the general bac- terial conditions and quality of pas- teurized milks, the bacterial counts as standards are, as has been indicated, very useful, but reliance should not be placed upon them as accurate indices of the efficiency of pasteurization op- erations. Here again, they would be of more value if there were available for correlation with them, the fully detailed information covered by a his- tory of the milk up to the time of heat- ing and of testing. Pusrtic HerattuH ASSOCIATION (c) Biological Demonstrations of Efficiency, Procedure C. C. Another procedure employed in the estimation of the efficiency of pas- teurization operations, calls for the de- termination in the pasteurized product of the presence or absence and the numbers if present of bacteria of the B. Coli group. Rarely also are tests made for the presence or absence of streptococci. Still more rarely are they made for species or groups of pathogenic bacteria or other micro-or- ganisms and then only if cultures of them have been added to the raw milk intentionally under experimental con- ditions, or if they have been found to be present in the raw milk. It is obvious that in all of these cases too, it is quite essential to have available for comparison the results of quantitive determinations of the presence of the same types in the raw milk, for otherwise any negative re- sults in the tests of the pasteurized product have but little significance. These quantitive determinations in the raw and the pasteurized products yield far more valuable results for pur- poses of judgment of the effectiveness of the heating process than the com- parative total bacterial counts on the same products, for the reason that members of these groups are more uni- form in their respective susceptibili- ties to heat, and in fact to all alterations of environment, than are the various types of bacteria of all sorts. More- over, these groups and species number among their members, races and strains which are themselves pos- sessed, at times at least, with the power of producing human disease. They furnish therefore the means for a closer judgment of the probable ef- fects of the processes studied upon the wider range of pathogenic bacteria of the non-spore forming types if the lat- ter had happened to be present in the product under the conditions of the PASTEURIZATION OF heating. Not until recently, however, has science been in the position to ap- preciate the value of the results of such tests when made on a routine basis. The question of the relative susceptibility to heat of the various members of the B. Coli group and also the relative frequency of them in milk have been answered in part. This is also true of the members of the groups of streptococci. Extensive laboratory and some practical studies had been made by numerous workers on the thermal death points, in the presence of milk, of the various pathogenic types of bacteria but the opportunities for making tests with truly pathogenic bacteria in the raw product and the numbers there present known have been extremely few. B. Coli as an Index of Efficiency. In one series of tests made under the direction of two members of the Com- mittee, Dr. H. D. Pease and Mr. S. AI. Heulings, strictly pathogenic types, B. typhosus (Hopkins); B. diphtherae; B. tuberculosis (both bovine and human varieties), were added in large numbers to volumes of milk possible of practical treatment in an apparatus which had been for several years in active commercial use in a fair-sized plant. Tests were applied for their presence in samples collected at all important stages in the process. Upon all such samples, quantitative fermen- tation tube tests were also made for the presence or absence of those forms of B. Coli which are commonly present in milk. It was possible. therefore, in: this series of tests to make rather di- rect comparisons between the suscep- tibilities of each of the pathogenic types named and of the milk B. Coli forms, under the same conditions of temperature and time period of expos- ure. The results of these investiga- tions are of special value as they offer strong support of the use of quantita- tive tests for the presence or absence MILK 21 of B. Coli in the heated product, as a ~ means of indicating pasteurization effh- ciency. It can be stated that in no case were any pathogenic bacteria found in samples of the heated and held milks when the latter did not con- tain also the presence of substantial numbers of living B. Coli and in many of the samples in which B. Coli were found present in small numbers no pathogenic bacteria were detected by the most careful searching. Some of the pathogenic types and some of the B. Coli were found living after heating from 14@ to 141 degrees F. and holding for 15 minutes, but none of the former were alive after 30 minutes, while B. Coli were still present in 1 c. c. tests, but were not found after 45 or 60 min- utes holding at these temperatures nor with 30 minutes holdings at higher temperatures. In short, the greater tenacity of life of the B. Col in the medium time periods of exposure to the medium temperatures was clear- ly indicated. The conclusion is certainly war- ranted that the B. Coli forms com- monly found in raw milk are at least not more susceptible to the usual tem- perature and time exposure conditions of pasteurization than are B. typhosus and B. diphtheriz. In the case of B. tuberculosis, the comparison must be made between the effect of the heating process upon its power of infection of guinea pigs as compared with the growth power of the B. Coli in lactose bile tubes. Since the time of these investiga- tions (1911-1912) much work has been done by Rogers and by Ayers and their respective associates, on the means of separation of the B. Coli group into the two types of true B. coli and B. aerogenes and of the rela- tive frequency of them in cow manure and cattle fodder as well as in milk. Ayers and his associates have shown the relative occurrence of these two 22 Tuk AMERICAN forms in milk produced and handled under several of the most common commercial conditions. Neither they nor have others shown the relative susceptibilities to pasteurization tem- peratures of the two sub-groups. How- ever, this information when available may be of greater scientific than 'prac- tical value, for if those of one sub- group are shown to be more suscep- tible to the heat than the other, the practical fact would not be altered that in an efficiently performed pasteuri- zation operation none of either of them should be found alive after the minimum standard temperatures and time periods of holding when the standard method for determination of them in 1 c. c. were used. It is to be strongly recommended that similar quantitative tests be made upon the raw milk just before pasteur- ization and upon samples of the prod- uct upon the completion of each of the several important steps in the heating and cooling processes, such as samples from the first and last milks out of the heater, and one or two intermediary ones; from the first and last milk from the outlet of a continuous flow tank or pipe holding system and several in- termediary ones; from the milk at the beginning and at the end of each hold- ing period from a batch pasteurizer; from the first and last milks over the cooler and at several intervals in be- tween. Of special importance in this con- nection have been the demonstrations that substantially all market milks produced under commercial conditions and even the majority of certified milks will show positive results in the application of the standard tests for the presence of members of the B. coli group in |. c. ¢.,innoculations. Ayers and Clemmer have recently published more elaborate studies on the occur- rence and significance of the colon count in raw milk and one of their Pusitic Heart ASSOCIATION conclusions is that “fresh milk pro- duced under the best conditions al- ways contains some organisms of the colon aerogenes group.” While, there- fore, it is recommended that in all tests to determine the efficiencies of pasteurization process by the use of quantitative determinations of the B. coli group, samples of the raw as well as those of the fully and partially pas- teurized product should be collected and tested, it is evident that the results of such testing of samples of the raw and of the intermediary product are not as necessary for final judgment as are the results of the bacterial counts of the same or similar samples when only total counts are available. When a fairly detailed history of the product is available one familiar with the sub- ject can obtain much valuable infor- mation and may even be able to express a tentative conclusion of the first, last and intermediary samples of the final heated and held product even if no such tests have been made of the raw milk. Streptococci in Relation to Pasteuri- zation. With respect to the use of tests for the presence of streptococci in pasteurized milk, the Committee knows of no published reports of studies conducted under truly commer- cial conditions. However, there have been a number of intensive investiga- tions conducted under laboratory and semi-laboratory conditions. Davis* made extensive studies of the streptococci found in various types of milks, i. e., certified and pasteurized, by both the flash and the holding sys- tem. His work deals chiefly with the haemolytic forms. His conclusion that of the strains of the Streptococcus lac- ticus some are haemolytic and some not, although neither are virulent for animals, is of importance. He found the various haemolytic forms more *Davis, Journal of Infectious Diseases, 1916, 19, p. 286, and 1918, 28, p. 559. PASTEURIZATION OF MILK 23 often in certified milk than in the pas- teurized. Some of them were of the human variety as indicated by various tests applied. ; Avery and Cullen** have divided the haemolytic streptococci into two groups by means of their final hydro- gen ion concentrations. Their haemo- lytic group includes both those of human and of bovine origins. They showed that substantially all of those of human origin reached final concen- trations of pH. of from 48 to 5.3, whereas those of bovine types with but few exceptions and those of more or less doubtful bovine origin reached Pu. of from 4.3 to 4.5: They propose a method of rapid differentiation of these two types. The most applicable researches to the problem before us are those of Ayers, Johnson and Davis.* They in- vestigated a wide range of organisms collected from many sources. By va- rious tests both by cultural and animal inoculation measures they divide them into two groups. Those of Group A were all haemolytic many of them pathogenic and all had thermal death points of 140 degrees F., (60 degrees C.), or lower—chiefly lower. The other Group B., contained a very few con- cerning the pathogenicity of which there was some question, but they were chiefly non-pathogenic and were generally non-haemolytic, and the ma- jority had high thermal death points. They likewise correlated the two groups thus separated with a division through the application of the results of hydrogen ion determinations. Thus the A. series gave Pu. figures of from 5.4-6, while the B. series showed from 4.5-4.7, They believe that pathogenic streptococci (Group A. type) are de- stroyed by the proper pasteurization of milk at 140 degrees F. (60 degrees C.) for thirty (30) minutes. They feel **Avery and Cullen, Journal of Experimental Medicine, Vol. XXIX, No. 2, February 1, 1919, p. 15. z *Ayers, Johnson and Davis, Journal of Infectious Diseases, 1918, 28, p. 290. it desirable to have their work con- firmed before coming to any definite conclusions. The Committee feels that while enough has been done to indicate clearly that a proper application of heat to a temperature of 140 degrees F. for a minimum period of thirty min- utes will destroy substantially all the pathogenic streptococci in milk still they believe as already expressed that a margin of safety for biological rea- sons calls for the use of higher tem- peratures of not lower than 145 degrees IX The Committee does not feel that there has as yet been suggested any easy and reliable bacteriological method for the determination of pasteuriza- tion efficiencies by tests for strepto- cocci in the final product or by a com- parison between the findings as to these forms in the raw and pasteurized samples. As to studies upon other groups of. bacteria having pathogenic powers, there is but little requiring comment. In so far as bacteria of known patho- genic properties is-concerned, the op- portunities for their use in determina- tions of the efficiencies of commer- cially operating pasteurization proc- esses will be very infrequent. Of ne- cessity these bacterial forms must have gained access to the milk acci- dentally and have been found present in the raw product and their approxi- -mate numbers there determined, be- fore any failure to find them in the pasteurized samples would have sig- nificance. The epidemiological evi- dence as to the relative infectivities of the same milk, raw and pasteurized, would of course, be far more valuable. The occasions in which it would be warrantable for known pathogenic types to be used would be in instances where the apparatus was experimental in character and_ the milks to be treated in them were never to be offered for human consumption, only 24 Tue AmericAN PusLic HEALTH AssocraTION (d) Application of Tests to Demon- strate Efficiency. Up to this point, consideration of the methods and sig- nificance of the results of biological tests has been given on a more or less theoretical basis. It would be well to point out some of the most disturbing factors in the application of the tests discussed. Tests for Sterility of Apparatus. From what has already been stated the conclusion must be self evident that the results of any study for the de- termination of the real pasteurization efficiency will be of little or no value if corroborated evidence is not avail- able demonstrating the substantial sterility of the entire apparatus of the pasteurization system including the cooler, before the run starts. In fact, the first and most important element in such a study consists in the deter- mination of the existence of such a sterile condition. When this is not possible, and it is true that many forms of commercial apparatus are substan- tially impossible to sterilize, it be- comes necessary to collect a series of samples of waters of condensation or of previously sterilized salt solutions used as wash waters and to determine through the testing of them, the real bacterial condition of each and every important section of the apparatus be- fore the treatment of the milk begins. This involves a considerable amount of labor and on many occasions even with such results available for consid- eration along with those of the tests on the samples of the raw and fully or partially treated milks, it is not pos- sible to come to any definite conclu- sions as to the real efficiency of the heating processes studied. One of the compensations arising cut of this substantial difficulty comes from the fact that every study of the heating efficiency of a system must of necessity, determine the efficiency of the cleaning operations applied to each section of the apparatus at the close of the day’s run. While uncleanliness of apparatus is largely a matter of old milk, either dried on or moist and in a variable condition of bacterial incubation and while these conditions may not lead to any very direct health menace to the adult consumer of the product even when these conditions exist in the ap- paratus handling the already heated and held milk, still they are most ob- jectionable from other standpoints. They tend greatly to reduce -the gen- eral quality of the milk in that they promote rapid souring or other spoil- age, and they tend to the develop- ment of objectionable flavors and tastes in the product. In the determi- nation of the condition of sterility or cleanliness of pasteurization apparatus or of any milk handling utensils, the following procedures are offered as having given excellent results. Samples of any water of condensation resulting from the steaming of the apparatus should be collected and test- ed both for total bacterial count and for the quantative presence of B. coli using inoculations of 1 c.c. and of smaller amounts when the washing and steam- ing processes have been obviously de- ficient. Such waters of condensation are obviously to be looked for at the lower or dependent portions of the ap- paratus. The points of collection should be selected also with the idea of ob- taining information as to the condition of each important unit of apparatus in the system, i. e., weigh and receiving tanks, heaters, holders, cooler, fillers, etc. To collect the same it is often only necessary to unloosen the couplings in the sanitary piping at the lowest points. But in many cases the inspector must use considerable ingenuity in order to obtain sufficient amounts of such waters without contaminating them. Where there is no water of condensa- tion the use of 200 c. c. of sterilized 35 PASTEURIZATION per cent solution of sodium chloride may be advantageously employed as a wash water, with the collection of as much of it as is possible after it has flowed or been washed over the milk contact surfaces. Sterile spoons of the tea or dessert spoon size are very use- ful in the collection of samples of such waters when the latter are small in amount and are in otherwise inacces- sible portions of the apparatus. They make it possible to remove by physical force with the wash or condensation water perceptible portions of the greasy films on the metal surfaces which almost invariably harbor exces- sive numbers of bacteria. The tests should be performed by the Standard Methods of Bacteriological Water Analyses of the Laboratory Sec- tion of the A. P. H. A. Tests for Defects in Design or Oper- ation of Apparatus. In addition to the collection of the samples for the deter- minations of the sterility of the appara- tus, samples of milk, foams, drips, etc., should be collected from each unit of apparatus to check up the possibilities of inefficient pasteurization treatments due to defective mechanical design or of improper operation of the unit. At- tention has already been called to the more important of these possibilities in another section of the report. These samples are all in addition to those col- lected for the direct determination of pasteurization efficiencies. The latter should include the following and as many more as may be necessary to give a thorough picture of the effective- ness of each step and stage in the oper- ation: Samples of the raw milk at the very start of the run and at the very close and one or more in between depending upon the history of the milk under treatment; samples of the first, last and several intermediary in the run of the milk after heating and before hold- ing; the same after holding and_be- fore cooling and if there are several or Mik 25 steps in this portion of the operation then samples from each should be taken; the same after cooling and before passing into the can or bottle fillers, also after leaving the fillers and before entering the cans or bottles and finally from the cans and bottles. The samples of the product in these later steps in the process are to be collected and tested with the object of determin- ing the possibilities of reinfection of the already heated and held milk. All such samples should be subjected to the standard procedures of the Lab- oratory Section of the A. P. H. A. for the bacteriological examination of milk for total counts and for the quantita- tive determinations of B. coli by the standard methods of bacteriological examination of water of the same Sec- tion. Interpretation of Results on Tests of Efficiency. When the results on the cleanliness samples do not show the absence of B. coli in one c. c. tests of all drips and condensations and wash waters, and very small numbers of bacteria or none at all, the cleaning and sterilizing processes should be con- sidered as deficient. When the results of the tests of the samples of the milk from the holding system indicate the presence of B. coli in 1 c. ¢. inocula- tions, further or careful and critical study of operations of each step and stage in the pasteurization process are called for. When the results of the tests of the samples taken at any stage after the holding show the presence of substantially larger total counts of the presence of larger numbers of B. coli than were found in comparable samples of the milk from the holding system, reinfection of the milk is indicated and the cause or causes of the same should be ascertained by further study. (5) Conclusions on the Analytical Control of Pasteurization Plants. It is evident that the analytical control of pasteurization plants calls for the car Tare active co-operation of engineers and laboratory investigators and that any complete or satisfactory study of even one plant calls for considerable effort. The great importance of efficiency in the ever increasing application of pasteurization processes to market milk and cream and other dairy prod- ucts warrants a cancentration of ef- fort by both official and industrial agencies upon this phase of milk and dairy product supervision, even, if necessary, at the sacrifice of other in- spectional or analytical investigations, the results of which do not have such a direct bearing upon the actual pre- vention of the transmission of disease. VII. State and Municipal Supervision of the Pasteurization of Milk. The Committee has carefully review- ed those parts of the milk ordinances, governing pasteurization, of practically every city of over 25,000 inhabitants in the United States, and does not feel that any one of them affords the full protection against ineffective pasteur- izers and faulty operation that should be assured for so important a process. The legal authority controlling pasteur- ization grades all the way from ordin- ances that merely state that milk from tubercular cows shall be pasteurized and then do not define pasteurization, to the more complete and carefully thought out laws governing pasteuriza- tion plants for New York, San Francis- co and Chicago. In the opinion of the Committee, none of them are adequate in light of careful studies of the various types of pasteurizing apparatus and the careless handling that frequently is met. In reviewing many of the ordinances, the Committee has been impressed with the feeling that the framers of the re- gulations look upon pasteurization as merely a means for putting dirty milk on the market, without too greatly jeopardizing the health of the con- AMERICAN Pupbitic Heatrtir ASSOCIATION sumer. This is a great mistake, and no ordinance should be so worded as to permit a feeling to arise in the minds of the public that pasteurized milk is necessarily inferior to raw milk; in fact. if any impression is to be given by such regulations, it should be that pasteurized milk is preferable to the raw product. In the opinion of the Committee, any ordinance to be com- plete and effective must contain the following points: A definition of pasteurization ; a statement of the tem- perature and time that shall be used: temperature to which milk shall be cooled, etc; the objects to be obtained, namely ultimate bacterial count, etc; regulations governing construction of the apparatus and equipment; control, namely, the organization to have super- vision of the process; and finally, pen- alties to be imposed for failure to com- ply with the provision of the ordinance. (1) Time and Temperature Require- ments. The Committee feels that no milk should be considered pasteurized that has not been heated to a tempera- ture not lower than 145 degrees F. for not less than 30 minutes. Technical investigations have demonstrated that the germicidal action of increasing de- grees of heat for longer and longer time periods is progressive in charac- ter; that is to say, that temperatures substantially below 145 degrees F. have a more and more injurious action upon some of the disease producing bacteria which may be in the milk under treatment, both as the tempera- ture is increased and as the time of its application is prolonged. While the action of these amounts of heat for these periods is progressive in charac- ter, it is the opinion of the Committee that this factor must not be considered as justifying any failure in the opera- tion of any form of apparatus or sys- tem to apply the appropriate degree of heat for the full time period to every particle of the product. In other PASTEURIZATION OF words, this factor does not justify the averaging of the temperatures of differ- ent portions of the product under treat- ment at any particular time period. It is the opinion of the Committee that a temperature of 145 degrees F. applied for 30 minutes to every particle of the milk under treatment consitutes a pro- cess which can be applied under ap- propriate practical conditions without endangering what has been popularly known as the “cream line” of the pro- duct. It should be specified that pas- teurized milk shall be promply cooled to and maintained at 50 degrees F. or below, a principle which should be ap- plied to the handling of all milk. (2) Department to Control Pasteur- ization. The Committee feels that the control of pasteurization plants in the various states is properly a function of the state health departments, except in those cases where the municipal health department has a division for milk work exclusively, organized on an efficient basis that will give the municipality competent supervision and control of not only all the milk within the municipality but also its production, preliminary handling and transportation. This division having a superintendent and assistants with an organized staff of inspectors for the inspection of the sources of the supply _and all creameries or shipping stations through which the milk passes; also bacteriological and chemical labora- tories in charge of technical operators and assistants; an engineering staff in charge of a chief engineer, compet- ent to pass on the construction of dairy buildings and apparatus and direct the operation of the apparatus and also a system of rules and regulations, that when enforced will insure safety to the public in the matter of the milk supply. It is probable that a majority of the existing pasteurizing plants will fall under municipal control, but grad- ually more and more plants are being Mitk 27 constructed in outlying districts to which municipal authority cannot well extend, and these should be covered by the inspection service of the state health departments, and should be un- der their authority. At present in several states the supervision of pas- teurizing machinery is a function of the department of agriculture. It is the opinion of the Committee that the control of a process so fundamentally allied with health as is the pasteuriza- tion of milk, lies properly with the health authorities, rather than with the department of agriculture. The state health department should promulgate minimum standards for the control of milk pasteurization, which may be supplemented by the munici- pallies to fit their peculiar needs, but in no case shall the minimum standards of the municipality be less than those for the state at large. Again the health departments of the various states are equipped to undertake the medical, engineering and laboratory work that is absolutely essential, if proper super- vision and control of the design, con- struction, and operation of milk pas- teurization plants is to be maintained. The prosecution of failures to pasteurize milk properly is naturally a function ot the health department. (3) Requirements Regarding Ap- paratus. A special permit should be required by the state department of health or by the municipality having an adequate health department for the erection or alteration of a pasteurizing plant, and the issuance of this permit should be based upon plans, specifica- tions and detailed drawings, submitted to that office for their permanent files. This recommendation is in line with the procedure already adopted for water supply and sewerage systems. These drawings should be carefully studied in the light of the information relating! to the defects and their dan- gers commonly found in pasteurizing 28 THE AMERICAN plants as brought forth in the preced- ing pages of the report of this Commit- tee, and the permits withheld if there is any possibility that defects in the design may jeopardize operation. Not only must the design of the proposed pasteurization plant be free from de- fects, but provision must also be made for accurate control of the process, and for the securing of complete rec- ords of the operation of the plant, as shown by recording temperature and time devices on the heater holders, and cooling apparatus. (+) Qualifications of Plant Oper- ators. The pasteurization of milk re- quires not only a proper building and efficient apparatus for treatment of the milk and sterilization of the containers, but, also, competent, efficient and re- liable operation of the apparatus. This requires that the prospective operators should have special training at a dairy school or under an experienced and competent operator of a pasteurizing plant, before being allowed to assume the charge of a plant. To bring these operators closely under legal control, no person should be permitted to have supervision of the pasteurization of milk or to operate milk pasteurizing apparatus without having passed an examination conducted by the health authorities. This examination should show that the person is not only com- petent to operate the apparatus, but is also familiar with the laws relating to this work and the responsibility of the supervisor or operator to the pub- lic. A license at nominal cost, renewable annually, should be issued by the health department to person desiring to en- gage in this work and who show they are qualified to perform it. The sus- pension or revocation of such a license for careless or improper work on the part of the licensee should render it impossible for such person to be em- ployed in any dairy work within the Pustic HEALTH ASSOCIATION jurisdiction of the health department issuing the license until reinstatement. (5) Bacterial Results on Pasteuriza- tion. There is probably no one phase of the pasteurization problem that is occasioning more thought and contro- versy than that of the bacterial results to be demanded. The Committee feels that this is a problem to be studied in each community, and the limit set as a result of such investigation. Cli- matic conditions, length of haul, type of conveyance as by auto truck, refrig- erator car, a common baggage car, and many other factors, each affect the bacterial content of the raw milk, and , with it the content of the final prod- uct, so that the Committee does not believe it possible to specify a mini- mum standard that can be used nation- wide. Any such standard would per- mit of careless operation of pasteur- izers in some cities, and with it the placing of inferior milk on the, mar- kets; while in other cities it might be- come either a question of violating the ordinance or going without this article of food. The ordinances of several cities specify a 99 per cent removal. Noth- ing could be more ridiculous, for in cases of raw milk with a low bacterial content it is impossible to secure a 99 per cent removal; while with a very high content a removal ‘of a greater percentage is readily affected, and 99 per cent represents an inferior product, and yet the percentage required can be met even with faulty operation. (6) Penalties for Violations. To insure compliance with an ordinance it is unfortunately necessary to pro- vide penalties for failure to do so. The severity of penalties varies more or less throughout the country, and it is best that this feature of any milk or- dinance be prepared to conform with practice in that district. The Com- mittee feels that, in order to insure convictions for violations of those fea- PASTEURIZATION OF MILK 29 tures of the ordinance governing the character of the milk and its bacterial content, the regulations should be spe- cific on how samples shall be collected and handled. For example, in some regions the agent of the health depart- ment takes forth a few cubic centi- meters out of the bottle with a sterile pipette, and takes this sample to the laboratory in a_ sterile con- tainer. The dealer thus always has the opportunity to claim that the pip- ette or the container were contamin- ated, or that the wind was blowing street dust over everything, while the sample was being collected. The Com- mittee is inclined to favor the pur- chase of an entire bottle of milk direct from the delivery wagon, and sending this in an iced container.to the labor- atory for analysis, for then the dealer cannot complain that contamination was introduced in sampling, but on the other hand it does not allow the dealer an opportunity to get a check on the same sample. Milk that is sold as raw or with- out any marking or labeling whatso- ever, is notice to the public that the milk should be cooked before use in order to protect themselves against any possible infection that may be carried by the milk. Milk that is sold as “pasteurized” conveys to the public the impression that no cooking or fur- ther safeguard is required. Any use of the word “pasteurized” or of any designation or marking that may create in the mind of the public the impression that the milk has been pas- teurized when it has not had efficient pasteurizing treatment, or has been ex- posed to possible infection by having had the package tampered with, or bears an incorrect date or any other incorrect data, should be made by law a criminal use of the word “pasteurized.” This should subject the person or persons guilty of such crime, or the person or persons by whose direction, or connivance such crime was consumated, to prosecution and such heavy legal penalties, as will insure full protection to the public health in the matter of pasteurized milk. The word “pasteurized” when ap- plied to milk, should be limited by law to designate raw milk that has been produced and handled under sanitary conditions, that is of good bacteriological, chemical and physical condition, before pasteurization, that has had efficient pasteurizing treatment under competent and responsible oper- ators and supervision, that immediately after pasteurization and in the con- tainer when delivered to the consumer, does not have an excessive bacterial content, and that has not been exposed to unnecessary risk of infection after pasteurizing treatment. These require- ments should be fulfilled in order that the public will not be deceived when they see the word “pasteurized” on a package of milk. The opening of a package contain- ing pasteurized milk in any place not licensed by the health department as a milk plant or store, or by any person not authorized by the health depart- ment to handle milk, previous to its delivery to the consumer, is an un- necessary risk of infection and should be prohibited. The sole object to be attained by pas- teurizing milk is the elimination of any pathogenic organisms that the milk may contain. Therefore, the treat- ment must be obsolutely efficient, and unnecessary risk of infection after treatment must not be permitted. Pas- teurization is under no circumstances to be considered as a renovating pro- cess; unhealthy operators, insanitary surroundings, and careless or dirty methods of handling the milk, must not be tolerated. 30 Summary. Information collected throughout the United States and the Dominion of Canada shows that there are approx- imately 4,200 pasteurization plants in. operation in these countries at the present time and that only’ a very limited number of these installations are controlled from a public health point of view. There is little uniform- ity in the definitions of milk pasteur- ization used by Federal, state and mun- icipal branches of government which leads to miuch confusion as to the proper meaning of “pasteurized milk”. There is also a very apparent lack of understanding on the part of the pub- lic regarding the actual meaning of pasteurization and the reason for its general application. The results of scientific workers on the effect of pasteurization on the com- position of milk indicate that there is little, if any, change in the chemical composition so far as can be determined by chemical analysis. A large amount of experimental work has been con- ducted on the undesirable effects caused by pasteurization on milk that is to be used for infant feeding. Some conflicting opinions have resulted from this work but it is now generally re- cognized that any ill effects from the use of such milk for infant feeding can be easily remedied by the addition of certain common substances such as orange juice and potato water. The protection that pasteurization affords older children and adults from com- municable diseases far overshadow any of the easily remedied ill effects as- sociated with infant feeding. The evidence presented on the var- ious methods used for the pasteurization of milk indicate that the “holding” sys- tem is so much superior to any other as to justify its universal application for the pasteurization of milk to be used for human consumption. The THE AMERICAN PusLic HEALTH ASSOCIATION process of pasteurization of milk should consist in subjecting the milk to a tem- perature not lower than 145 degrees F. for not less than 30 minutes. The mechanical features of pasteur- ization plants has not been given suffi- cient attention by many of the depart- ments supervising the pasteurization of milk, and defects in pasteurizing ap- paratus are found in many plants now in operation. Defects may be found associated with nearly every part of pasteurization apparatus which can be eliminated by proper de- sign, construction and operation of the plant. Jt is possible to construct a commercial pasteurization plant on a practical basis without inherently dangerous defects. Such a plant when properly operated should produce a pasteurized milk which is safe for human consumption. The analytical control of pasteuriza- tion plants is a subject that has been given considerable attention by health authorities and many methods have been studied for determining the ef- ficiency of pasteurization plants and the various apparatus associated with the pasteurization of milk. The meth- ods discussed in this report include the physical, chemical, physico-chemical and biological. The physical methods involving the testing of sensitive in- struments used to control the process, and biological tests to study the ef- ficiency of plants and the quality of their effluents appear to be the best of those already devised and applied on a practical basis. It is clearly evi- dent that the analytical control of pas- teurization plants calls for the active co-operation of engineers and labora- tory investigators before satisfactory interpretations can be made and effic- ient results accomplished. State and municipal supervision of pasteurization should involve certain fundamentals for the protection of the public health. It appears to be gener- PASTEURIZATION OF MILK ally recognized at the present time that the branch of government to which this supervision work should be assigned is the health department. ‘his makes possible the correlation of this work with other health activities that are primarily directed towards the suppression of disease. The state should at least set minimum standards for the control of milk pasteurization which may be supplanted by the mun- icipalities to fit their particular needs. The supervising health department, organized for the control of milk pas- teurization, should have available en- gineering, laboratory, and medical ser- vice. The approval of the health de- 31 partment should be required on the system and equipment of each plant producing pasteurized milk. A large part of the supervision should be con- centrated on the construction, opera- tion and management of the plant and its equipment. The operators of such plants should have had proper train- ing and be licensed by the health de- partment. Milk should not be sold as “pasteurized” unless its production and sale is properly legalized and super- vised by competent health authorities. Laws and ordinances’ governing pas- teurized milk should be specific in every detail and should provide ade- quate penalties for offenders. t 32 THe AMERICAN JOURNAL OF PupLtic HEALTH TABLE OF CONTENTS Ey Untrodtenon, 2 c.sses means aentouterts gg tema w ames ota porenia agus RemE 2 lI, The Present Status of Milk Pasteurization. ...... 0... cece cece e ence eens 2 (1) Number of Plants in Operation..... (Ae Se EBE Dewees vented ees es 2 (2) State, Territorial and Provincial Control............ 0. eee eee eee ee 2 (2) Municipal Control.................. ee ee eee 2 (4) Definitions of Pasteurization. ys vvisse sores dcyaweeet peg es eae Save e RES 3 (5) Apparent Lack of Control and Uniformity of Methods.............. 3 (6) Absence of Public Understanding of Pasteurization................. 3 ill]. The Effect of Pasteurization on the Composition of Milk..................00. 3 (i): effect of Heat on Milk wndgs comme sewuaasaqunainyantiundaa me ead de 4 (2) Infant Feeding Experitients.::.ane voseavees ever veeneriendesseeaias 4 (3) Infant Feeding vs. Communicable Disease.............. 2.000 c evens 5 IV. “The: Process of Mlk: BastemrizatiOntin csc iscscidwenginns 2 mates apm nawnesaauniens 6 (1) Helding System: R€qiited sc. coccaceesausennnemes amen gy gine agree ee 6 (2) Pasteurization Process Defined............ Bugis hc mistlune barad coe 26 V. The Mechanical Features and the Operation of Pasteurization Plants........ 7 (1) Methods of Pasteurization.................0. sidan diwaed hie eatnrecece ae 7 (2) Pasteurization if. thé BOttléns ccc csavaeais cater aaanews saw eua ces ee v4 (3) Pasteurization with Intermittent and Continuous Flow Apparatus.. 8 (a) Blow ‘Controllersiuxwsy sanas es aciae p2 AGRE 2 damescicdsoobune on eondd am 8 CB) | ELE AGELESS copete ¥ cay io ais cseds «coisa aap dude scream saccaduade sw amctiaive atiechvantnane de anwdahiars 8 GE). PLOTTER Se cova nitrite one eeunten Ah ia vaaberaic oaavlacchee =k an aviece pce onthe: vice toatln er 9 Cd) AG OOLEES. izeadenshs demertiare Ga aioe are ee ea Saeed b enema soem Ae eee ees 10 Cede) Burp sy are gakeuils s eeitan > emateuacunnee Aeaeens adeeb vee as cen esas di CG) Stuffing Boxesx: ay ses vavsaed eeenes shaacambuas duane ywney ies 11 Ce) (Bittnes cand “Wel eSy .scccnis a asiaitce a deidare acharntamiend deaniea eee ase araeed 11 (h) Metals Used in Construction of Apparatus.................05 11 (i) Téiipérature Control, Apparatus’ cass comnsees ag van deo¥ate cas 11 (j) Temperature Recording Instruments and the Interpretation of Recording, (Ghar tsncae cman Yc cee nective basunhinn dea aary ymewacd ea 12 (k) Cleaning and Sterilizing Apparatus...............0.000000008 14 (4) Some Dangerous Defects in Pasteurization Apparatus............. 5 VI. Analytical Control of Pasteurization Plants.............. ccc cceeeecseeeceees 16 GQ) Physical Method Seco ccans sycnsie De wuareeeeeses eeu Lee's dcmalaw aa 16 (a) Testing of Time and Temperature Recording Devices........ 16 2) “Ge TATCa, AMC t IO MS sone iasirietniauase saci taie svanswacas patisiteg od pwns oramnasiis ure eseedig te ete 17 (3) Physico-Chemical Methods.....0..0cc500c0ecceege ded cbaveebeucnewee 17 (4). Bidlogical: -Methio dstngy.10 cocss/ga angers xaehadd ¢-¢agn v ERIS Seas das ausadnce discs 17 (a) Biological Demonstration of Efficiency Procedure A.......... 17 (b) Biological Demonstration of Efficiency Procedure B.......... 19 (c) Biological Demonstration of Efficiency Procedure C.......... 20 (d) Application of Tests to Demonstrate Efficiency.............. 24 (5) Conclusions on the Analytical Control of Pasteurization Plants..... 25 VII. State and Municipal Supervision of the Pasteurization of Milk............... 26 (1) Time and Temperature Requirements........ 00.00. c cece cece ees 26 (2) Department to Control Pasteurization......... aN re NOP Le eaten 27 (3) Requirements Regarding Apparatus...........00ce esc ee cece eee uceee pa (4) Qualifications of Plant Operators.......... 00.0 cece cece e cece nc eeee 28 (5) Bacterial Results on Pasteurization......... 00... cee e ees cececueces 28 (6) Penaltias f6P “Violations, Brew, J. D. and DotrerrerR, W.D. The number of bacteria in milk. N.Y. Agr. Exp. Sta., Bull. 439, 1917. ° Breep, R. S. and Srocxinc, W. A. The accuracy of bacterial counts from milk samples. N.Y. Agr. Exp. Sta., Tech. Bull. 75, 1920. ® See fifth reference in footnote 2. ” BREED, R. S. and Brew, J. D. Counting bacteria by means of the microscope. N. Y. Agr. Exp. Sta., Tech. Bull. 49, 1916. WERNER, Percy. Plan for control of milk supplies in small cities. Jour. Dairy Sci., 1, 284 — 289, 1917. 8 CoMMITTEE ON STANDARD METHODS FOR THE EXAMINATION OF WATER AND SEWAGE. Report, 4thed., 115 pp., American Public Health Assn. 1920. 9 SORENSEN, S. P. L. Ztschr. Biochem., 21, 131, 201, 1909; Ergebn. Physiol., 12, 393, 1912. Ciark, W. M.and Lusps, H. A. The col- orimetric determination of hydrogen ion con- centration and its applications in bacteriology. re Bact., 2, 1— 34, 109 — 136, 191 — 236, 1917. Ciark, W.M. The determination of hydro- genions. 317 pp., Baltimore, 1920. 10 Barnett, G. D. and CuHapman, H. S. Colorimetric determination of reaction of bac- teriologic mediums and other fluids. Jour. Amer. Med. Ass., 70, 1062 — 1063, 1918. 11 Meparia, L. S. ‘Color standards” for the colorimetric measurement of H-ion con- centration pH 1.2 to pH 9.8 Jour. Bact., 5, 441 — 468, 1920. 12 DearsTYNE, R. S. A study of the effect of cotton stoppers used in dilution blanks on the numerical bacterial count, and of other practices in the technique of bacteriological laboratories. Jour. Dairy Sci., 1, 512 — 516, 1918. 138 See second reference in footnote 5. 14 See fifth reference in footnote 2. of sanitary milk. Penn. 16 Hirt, H. W. The mathematics of the bacterial count. Amer. Jour. Pub. Hygiene, 4, 300 — 310, 1908. Breep, R. S. and Dotrerrer, W. D. The number of colonies allowable on satisfactory agar plates. N.Y. Agr. Exp. Sta., Tech. Bull. 53, 1916. 16 See footnote 5 and fifth references in foot- note 2. 1!See footnote 5. 18 See footnote 7. 19 CommissIoN ON MiLk Stanparps. Third report. U.S. Pub. Health Service, Pub. Health Repts., 32, 271 — 296, 1917. See also N. Y. City and N. Y. State Sanitary Codes. 20 Breep, R. §. and Brew, J. D. The control of bacteria in market milk by direct microscopic aenation. N. Y. Agr. Exp. Sta., Bull. 443, 1917. : 21 Model ordinance, Penn. State Dept. Health. Local ordinances, Butler and Reading, Penn. 22 Frost, W. D. Comparison of a rapid method of counting bacteria in milk with the standard plate method. Jour. Inf. Dis., 19, 273 — 287, 1916. Frost, W. D. Counting the living bacteria in milk. A practical test. Jour. Bact., 2, 567 — 583, 1917. *8 TonnEy, F. O. Organization of control of pasteurization. Amer. Jour. Pub. Health, 10, 716 — 723, 1920. 24 SCHROEDER, M. C. Dirt sediment testing. A factor in obtaining clean milk. Amer. Jour. Pub. Health, 4, 50 — 64, 1914. 25 RuEALE, G. L. A., and Kure, W. L. Germ content of stable air and its effect upon the germ content of milk. N.Y. Agr. Exp. Sta., Bull. 409, 1915. : Proucua, M. J. and Werter, H. M. Germ content of milk. 1. As influenced by the factors at the barn. Ill. Agr. Exp. Sta., Bull. 199, 1917. Ayers, S. H., Coox L. B. and CLemMeER, P. W. The four essential factors in the pro- duction of milk of low bacterial content. U.S. Dept. Agr., Bull. 642, 1918. 2) AnpERSON, J. F. The frequency of tubercle bacilli in the market milk of the City of Washing- ton, D.C. U.S. Pub. Health and Marine Hosp. Ser., Hygienic Lab., Bull. 56, 167 — 197, 1909. 27 Jackson, D. D. and Metta, T. W. Differ- ential methods for detecting the typhoid bacillus in infected water and milk. Jour. Infect. Diseases, 6, 194 — 204, 1909. *8 See footnote 4. 2) Hasrincs, E. G. and Horrman, C. Bac- terial content of the milk of individual animals. Wis. Agr. Exp. Sta., Research Bull. 6, 1909. SHERMAN, J. M. Studies on the production State Coll. Ann. Rept. for 1914 — 15, p. 299 — 305, 1916. “Baker, J. C. and Brerp, R. S. The reaction of milk in relation to the presence of blood cells and of specific bacterial infections of the udder. N.Y. Agr. Exp. Sta., Tech. Bull. 80 1920.