a ' . a : Og | ' $4 \ Ss bo. . La ' ce THE VISIBL™ QUALITY OF MARKET MILK AS AFYECTTN BY CLARZTPICATICN AND FASTEURIZAT ION, Thesis for Degree of N.S. Hisays Cgiwara 1915 THESIS o) The Visible Quality of Market Milk ae Affected by Clarification and Pasteurisation, Introduction. Like bread and water, milk is a wellenigh univereal food throughout civilised lands. Woreover, con- taining, as is shown by chemical analysis, certain solids indispensable in animal food in forms that are easily and readily digeated and assimilated, it is one of the most economical as well as one of the most important and valuable means of sustenance. Investigation shows that when milk is purchased at two dollars per hundred pounds, the actual covet of a pound of edible solids is only 15.7 cents; while the cost of a pound of edible eolids in beef, with beef at ten dollars and a half ($10.p0) per hundred pounds, is 34.3 cents. (The above is a comparison of the retail cost of milk with the cost of hind-quarter beef when purchased by the carcass), Again, one quaré of milk supplies practically as mioh of both protein and energy ae three-quarters of a round of beef of average composition, or of eight average sized eggs, and can usually ve procured, as suzzgested above, for considerably lesa money. Since, therefore, milk is so economical and valuable a food sunonly for the masses and since pure milk ie so vitally connected with public health, the question of an unadulterated surply of this necessity is an important and pressing one, 402297 Qe Qua Although as yet thia problem has not been entirely solved, a number of its phases have been definitely settied, In the first place we may safely state that cheap milk is apt to be poor milk and that an improvement in its quality must inevitably mean an increase in price. In the second place, it will be generally admitted that the conditions under which milk reaches our large cities vary greatly with oiroum- stances, This variation was especially noticeable firteen to twenty years ago when, though not transported eo far as it ia today, yet due to inperfection of handling and other carelessness on the part of the farmere, the milk suprly was upon the whole of a decidedly inferior quality. Due to regue lation initiated and practiced during the past ten years, however, conditions as regards both quality and quantity have noticeably improved, ‘Today it is recognised that the greater part of the dirt and bacterial contamination that used to characterise the marketed zilk is external to the cow, Admitting that a small percentage of this contamination comes directly out of the cow's udder and is thus unavoidable, yet Cleaner barns, cleaner cows, sterilized and covered pails and, above all, clenner milkers and a proper cahing of milk immediately after it is drawn, have worked wonders in solving this problem of a rure milk supply. Naturally the rigid enforcement of the above sug- ae joe gestions is adow process ae well as a diffioult one. If stringent laws were at once enacted and put into operae tion in many cities there would be a consequent milk famine, Again, the practicing of the above suggestions would inevitabe ly so enhance the price of milk as to render it prohibitive to the masses in the large cities, Hence, it is obvious that such inprovement may be by evolution rather than by revolution; it must ve stimulated and fosterad by education and an enlightened public sentiment end, incidentally, by paying the producer a higher price for his product. Until this desired goal is reached however, we shall be obliged to tolerate a milk supply of a lees than perfect degree of sanie tation. Wow to improve this milk of a doudtful qualify and to overcome ite dangerous tendencies during thie transition atazse, it is here recommended that all milk be properly clae rified and pasteurized. Since the process of pasteurization is not an expensive one, (coste about 35 sper 100 lbs, milk) pasteurized milk can be sold to the consumer at a reasonable price, and will be practically as sanitary and hygienic as certified milk, Thrnt pasteurization is annually being adoped by more and more cities and dealers is a atrong point in favor of this grade of milk. Only 5% of New York's milk supply aa foe was pasteurised in 1900, while in 1909 the percentage had increased to 25 and today one is safe in affirming that at least 33 1/3% undergoes pasteurisation, In Boston and in Chicago 50%, and in UWilwaukee aprroximately 75% of the total milk supply undergoes pasteurization before renching the ule timate coneumer. Hence to provide a more sanitary milk supply without a great incrense in cost until certified milk is a practicable possibility, the clarifieer and pasteurizer have been deniged, the first to eliminate the visible dirt or sediment, and the second to renier the bacteria less active and to kill the pathogenic bacteria entirely. It is very necessary, however, that this clarifieation and pasteurizae tion be properly done. To insure this, therefore, it is ine dispensable that all olarifying and vasteuriszing plants be frequently and carefully inspected by competent authorities. How Wilk is Handled in “iik Plant in the M, A. C. Dairy. Fach morning the milk produced that morning and on the previous evening as well as on the neighboring farae is vrougnt bright and early to the MW, A, ©. dairy. Here, vefore it paseee through the double ply of fine oloth, or strainer, into the receiving vat, ench oan is carefully weighed and sampled. Frou this receiving wat it is pumped into the heate er where it is heated to the desired tenper@ture. From here it is conveyed by meange of pipes and troughs to the clarifier, where those impurities that were so fine as to be able to pase through the double vly of fine eloth are removed, ?rom this clarifier it next passes into the pasteurizer and is pas- teurized immediately. “The surplus milk, that is, milk not required for the dairy'c custonere is separated by meane of centrifiizal creaz separators (DeLaval No, 60 with capacity of 4000 pounds per hour is here used), This systematic arrange- ment of machinery used for clarification, pasteurisation, and separation, respectively, is illuetrated by the accompanying diazram? Clarification, The milk clarifier resembiea the separator in appearance out differs from it in results produced. hile the separator divides the whole milk into cream and skin milk, each escape ing through its own spout, the clarifier, on theother hand, ay delivera the whole milk through the one syout. Ita funce tion is to remove not only the insoluble dirt or sediment particles whioh externally enter while the silk is being drawn or nfterwards, but aleo the intemal contaninations consisting of orokenedown udder tissues or pus corpuscles, which are inmriably to be found in all @ilk, souetines even to the extent of a million or more to the cubis cene timeter, This dirt collects on the inside of the vowle shall and should be removed iunediately after the process of clarifying is completed, From the hyzienie standpoint the removal of this organic matter is especially important. Otherwise, were it left in the milk, it would be the source of organisus which are likely to cause trouble. This is the oase vcecause the prezenee of such dirt weans oncterial infection, which in many cases is decidedly dangerous. I¢ will unquestionably be adwitted that milk whieh containes a large amount of dirt and consejguently a large number of bacteria will be far inferior in quality. So deqided an improvement over the now old-fashioned wilk fliter, which never did prove satise factory, is this mofiern clarifier doing ite work by centrie fugal force, that it io today being adopted more and more by oity milkesupply plants, oo Joo TEST. (In the following imvestigation the DeLaval Centri- fusal Wilk Clarifier, No. 110, Capacity 4000 pounds per hour, wae used). The milk to be treated was first pimped into the heater from the receiving vat and was heated to a teperae ture of from 70° to 80° FP, It was next conducted to the clarifier through an elbow pipe and open faucet in the regulating cover of this machine and thus entered the bowl. Here it was clarified by tha arpnliention of the prinoiple of centrifuzal force, and passed on through a spout to the pasteurizer. (I¢ should here be mentioned that the machine Should reach a uniform speed of 600 revolutions a mimte before the milk ia allowed to enter and that the inflow be kert uniform; otherwise an irregular rate of speed or sven of inflow would result in unsatisfactory clarification). Results of Test. Samples of this clarified milk when tested Ly the sediment tenter, 4, @., when strained throug: a cotton dise are usually highly axtisfnrctory. Yery occasionally, however, sone slight partioles of dirt are noticeable on this cotton disc. "hese particles, however, are probably due to contamie nation from external sources after the process of clarifica- tion has been completed. Again, light flaky, staffelike chaff, or something similar to chaff, wery infrequently is =e Baw found by testing in the milk after clarification has taken place. This contamination escapes renoval from the milk probably vecause of its extreme lightness in weight in come parison with its surface area, thus buoying it up and consee quently enabling it to enter into the outflow of clarified milk. As shown by the records in Table q, out of 153 sedimentesanples of each day's original or raw milk, 8 gamplea (5.23%) were found to be nearly clean; 64 samples (41.83%) fairly clean: 78 sanmpsaes (50.98%) moderately clean; while 3 santrles (1.96%) were found to be dirty. On the other hand, out of 153 sediment samples of olarified milk, 145 samples (94.77%) were found to be clean; and 8 samples (5.23%) nearly clean, See Table I, a2~Jeae TADTIN I, Report showing grading of samples taken each day. Grade each days milk as follows: il, “Clean, 2. Nearly clean. 3. Fairly clean. 4, *oderately clean. 5. dirty. & Filthy, Samnle of Criginal milk is taken in olean pint bottle from receiving vat @fter stirring well, Sauple of Clarified milk isa taken in clean pint bottle from pasteurizer before cisteurization after vcilk has paseed through the clarifier. Sample of rasteurized milk is taken in olean pint bottle fron onsteurizer after pasteurization ise completed, (In each day pasteurized milk is clarified before pase teurization),. a @ l0e= TABLE I, (Oontinued). Date Original Wilk Clarified Milk Pasteurized Hilk Oct.4,'14 Woderately clean Clean one 8 5 @ e eee * 6 ° nearly clean _ oe ” Ms @ clean @en n ” 7 eee 0 9 " « eae ® 10 e " «ow * 12 clean " — *u4 moderately clean " clean 915 @ a 0 ® 16 e 0 e ei. ] 6 " i" 2 . . nearly clean . 20 . " clean ® 21 n e 0 e 2a e e e e 23 ” # “ " 24 nearly clean ° " . 22 moderately clean . nearly clean 3 clean Nov, 1 fairly olean e ad " 2 moderately clean " e 8 3 e e e 0 4 e " 0 e 5 a a " a 6 " " " a e ” e « e ® e , 9 farily olean . . * 20 moderately clean ° " 8 12? @ « ® * 13 fairly clean " . e* 214 « " " \ 15 @ " a e 16 ® e 8 " i moderately clean " . . i e " fairly clean 0 dirty . clean * 21 moderately clean " . * 22 nearly clean ° nearly clean * 23 moderately clean " clean e 24 " " e e 25 e e ® e 26 " " ® e " « vate Dee.d @ 9 @ @aspeaesasaesseaeasaesseaseseseaeseaesa8eoase 8 tex o e Ss * eeLn @2a2s33383 3 30 Original Milk wo lles TABLE I, (Continued). Nov.29,'14 Moderately clean e fairly clean moderately clean e Géirty moderately @elean fairly clean moderately clean a fairly clean moderately clean fairly clean moderately clean fairly clean # ® ” @: nearly clean moderately clean fairly clean e moderately clean @ fairly clean 0 clean fairly clean @ Clarified Milk clean ” nearly clean @ olean ® nearly clean @ clean Q S2sesezszpezsesazazaepesaesaesezaaszdazs 8838 nearly clean olean @ Pasteurized !Hilk clean e nearly clean clean nearly Clean clean e nearly elean clean @ ZSZeBsasaeaz2aeseresetztaesaeaezeezeaaesaavsesa ®& ate Feb ® a a — = 2 2 1 16 19 20 23 24 28 r. i ee lauwe TABLE I, (Continu Original Milk 016,114 fairly clean moderately clean fairly clean Rf moderately clean nearly clean fairly clean " nearly clean fairly clean nearly clean fairly clean e moderately clean nearly clean modernztely clean fairly clean moderately clean @ nearly clean fairly clean # moderately olean 0 0 fairly clean e moderately clean fairly clean ” moderately clean @ fairly clean ed). Ciarified Milk clean " nearly olean clean ” nearly clean clean 0 Pasteurized Milk clean ” nearly clean clean " @ nearly clean e clean @ woljzeq - Pasteurization. The necessity for the pasteurization of milk is twoe fold: First, to destroy the pathogenic bacteria which so ofe ten are the source of disease, and second, to check the too rapid multiplication of other bacteria, which allowed to go unchecked as is often the case when milk slightly contaiminated is left exposed to a temnerature especially condudive to such multiplication, soon renders it unfit for use as a human food, The large number of bacteria in the average market milk is especially harmful to infants because a large percen- tage of the bacteria present belongs to the putrefactive or closely allied kind. Those are largely responsible for the mrevalenoe of diarrhea dnd general gastro-intestinal troubdles and, therefore, for the high mortality rate anong infants and children, Whewer raw or vasteurized milk in the more digestible is a question on which authorities, variously interpreting the few available facts, strongl, differ. This naturally gives rise to no Little discussion about the advnatages and disade vantages of pasteurization. VLet it suffice to say that the advantages when pasteurization is vroperly done easily outweigh the corresvonding disadvantages. Let it be borne in mind that properly pasteurized milk is decidedly different in character from merely bvoiled milk, Pasteurization may be carried on in any one of three ways; “iret, by the "holding or intermittent method; " second, by the "flashing or continuous methods; and third, by the *bottle or final container method,“ In all three ealheae of these methods the milk is first heated to a specific high temperature and is then rapidly and artificially cooled toa specific low temperature sufficient to check the sreed of bnoterial miltiplication. ty this general process at least 95% of the general mass of bacteria are destroyed, ths improving the keeping quality of the milk and rendering ita safe food. The first mentioned method of pasteurization generale ly known as the "holding or intermittent method," also known as "perfect vasteurization”® is as follows; The milk is first heated to comparatively a low temperature, somewhere between 140° and 155° FW, At 140° F, the minimum exposure should be twenty minutes. or every degree of heat above 140% F., however, this minimum may be reduced one minute. In no case, however, should the minimm be less than five minutes. This method is considered the most effective fron several points of view, and is therefore used most extensively, The second, known as the "flashing or continuous method" proceeds by heating the milk to a temperature higher than that desired in the "intermittent method," somewhere between 160° and 175° ¥F., and with less than 2 minute's expo- Bure. ‘The efficiency of this method depends naturally upon the lenzth of time the nilk remains in the wasteurizer. If the milk flows too rapidly, it will not be sufficiently heated, while if it flows too slowly, it is likely to vecome overe heated. The results, therefore, will derend uron the time of a<15-- exposure, which in turm depends uvon the speed of the milk flow. In the third sethod, comnonly known as the "bottle or final container method," the processi is somevhat similar to that of the “holding or intermittent method." It differs, however, in that the milk while being heated is kept either in a bottle or in a small oontainer, as the case nay be, ine stead of being contnrined in a large vat or vasteurizer. This method is vrefernable in at least one respect; viz., it does away with the chance of contanination that is possiole during the ca@ing, bottling and delivering of the milk pasteurized vy either of the other methods, It is, however, the most expensive method of the three, (Bearing in mind the facts that pasteurized uilk is just as prone to become infected or re-infected, if exposed, ng raw milk; also that once infected, the bacteria nultinly more rapidly herein vecause the germioidal properties of this milk have veen destroyed vy the heat attendant uvon pasteurie gation and the surviving bacteria consequently do not have so severa a struggle for existence, we must take care that ti + the pasteurized milk is kept cool and free from all possible contanination. Again, those bacteria that survive the process of nasteurization will multiply very ravidly if the milk is allowed to reach a warn temverature, and will thus usually change the taste to a rather bitter and irritating one. Some- times, however, this multiplication of bacteria produces no noticeable change in either the taste or the appearance of welbuae The milk under consideration). fhe tyne of pasteurizer used in the followings ine vestigation was the "Perfeotion,” which has a aapacity of 200 gallons of milk. “The quantity of milk to be pasteurized was first placed in the vasteurizer, where it wis heated by means of a revolving coil of pine extending horizontally acrosse the pasteurizer, through which coil hot water was passed. ‘Yhen the milk thus heated reaches a temperature of 140° ¥. the hent is shut off. “his temperature is kept approx imately constant for twenty minutes, then it is rnpidly cooled by the foreing of cold water through this snme coil. ‘hen the milk has veen cooled to 75° or 70° PF, ice and salt re mixed with the cold water in the tank connecting with the coil. The brine resultini from thia nixing is now foreed through this revolvinz coil. ‘she nurpose of this is to cool the milk to a temperature of 50° F. or below, as quickly as possible. ‘This temperature, it will be reoalled, prevents the too rapid mle tiplication of bacteria, See Saple JI. HkKecord of asteurization of Milk, « 10, 1914 to Nay 4, 1915), 2 ream $ Distinctness 3; Lump of 2 Date :Temp,. : of cream line ; Butterfat, 3 : 3 3 é : hardly seen : none : : " $ Some : , ; : ; : : S gy 3/4": . Detecean 62 Feb. 23 a 1/4: fairly dist. : slight : 74 =: Iardly seen ;: some ‘ Mar,123 8 aa; " ; " ; ae Gas BO , 298 fa; : 3 : : - 233 8 3/4; " : ” 3 Appa gs 2 1/4 ¥ " : " : 2 ae 4/2: " : slight : . 13; 1/2; " 3 large 3 : 23; bg : destroyed 3; . : e ~ . i] g “ 3 " 2 3 8 S : n : ” : “ : . : 50; Be a : hardly seen; slifht ; Way 3 3 84° destroyed : qvae 2 Mr igs 77 oS 3 " ‘ " ; " 4 e ~ - . Sampld the cream line was measured in neck from receivf©®T® Wt able to measure the absolute from pasteu comparison was made between the raw they were e}k. four hours, | o-1l8ee ¥rom the conmerical standpoint the practical value of this method of rarastuerization is deternined in the light of the followinz considerations; ‘hat vactericidal afficiene cy has deen secured; whit effect has this rasteurization had on the cream line; and what is the intensity of the cooked flavor or taste produced. it will readily be seen that the higher the temperature, the longer the exposure, and the more ravid the cooling, the better will be the results fron the standpoint of the destruction of voacterial life. ‘On the other hand, too high a temperature and too long an €xposrue so alter the paysical and chemical condition of the nilk that the cream does not rise naturally but Gomes more Gompletely enulsie fied, 14. @., the clusters cf fat globules sometimes break up ints smaller bodies, and occasionally thege zlobulee ag a ree sult, exist individually and independently. Agnin, an extrenely high tennerature or prolonged exposure develops what is known as a “Cooked flavor" in the milk, Furthermore, the nublic usually judges milk by the amount of cream that rises. This is especially true in the case of the vottled milk where the location of the “cream line* is go easily detected. This test, the only one used by the consumer in deciding upon the richness of nis milk, is, of course, not an accurate one for determining the riohe ness of nilk, but the avvearance of the cream line, too often serves 28 the only basis for judging the quality of aupply. =-19e< As this is his standard, care should ve takne that pasteue rization influenoe the oreaming ability of milk as little as possible where said milk is t. ve used for connercial pure poses, It might be interestinz to note that in Turcne cone ditions are otherwise. “here the customer isa accustomed to the receiving of heated or cven boiled milk and consequently has come to understand that a poor cream line does not necese gaarily mean milk thet is defieient in the norzal anount of fet. “he accompanying t2ble gives statements fron some authorities relative to the effects of heat oa the crenming A ability of milk, Gee Table IJfXfz, AWTHORS on Jae Table III. STATE MUN TS Nospeman (a) coccccccessese "Milk may ve herted to 145° ¥, for an hour without markedly influencing the crean line. if nilk is heated somewhat higher than this, say 148°F or for a longer time, ths cream lay- er will blend with the milk below, The heating of milk for half an hour at a temperature of 150°. or over, has the effect of entirely yreventing the rising of cream or of delaying it very materially, * Michels (OD) erccccccccccee"l55°F, for 1 minute affects cream Line 145°F. for 35 minutes affects creame DAVAZe (c) @eeennoneepnaee e line,* "at 71%, (159.89F,) the milk is affeoe ted and thse crenan vill not rise vroe perly," WAYd (A)ececcccsccecccee"xposure to 160°F, for one minute, or (a) (0) (c) (a) longer exnosure to 140°F. rre both safe," evThe “ilk Questions "Warket Dairying and Wilk }roducts,* by Michels * "ilk and Publio Health" by Savage. "pure Milk and the Public Health” by ‘Yard, awe leew The third point of consideration of the ;ractice ability of vaateurization, i. @., the question of the impore- tance of a cooked flavor or taste in nilk, is one that differs treatly with the locality concerned. In ‘turone, for example, wnere the majority of the consunersa are accustoned to heated and boiled milk, there is Little if any odjection on tiis soore “Nany of the consuners actually prefer the heated. nilk. From the atandpoint of the mil venders of this country, however, it is desirable to avoid this eorked flavor 2.8 4 result of tiie process of nastcuPization .8s much as rossible, "he Amerie can consuncr atrenususly objects to any such flavor. ‘he following table records statements authorities in regard to this matter of a cooked flavor or taste in milk 1:3 a result of p.steurization, See Taole IV, ead Jae TABILY IV. AUTHORS wing (A) cccccccccvccccccce Nackdy and Larsen (b) eeccce Mcihels (0). cccscccccccacs STATUMENTS, "Wilk may Le heited to 165°", if quickly cvooled aftervards without developing a boiled inste,"* "when milk is heated to 160°F., or above, it sssunes 4a distinctly cooked taste, which makes it dige emreeable as a food ror nany peonle "1509F. for 40 minutcs does not affect taste, 167°F, for scvcral Rosenon (d)revccccccscveces ard (O)ecccccccccccsecece Minutes taste affected," "She cooked or sdalded taste apperrs at about 70° C,.(158°¥.) and becomes more pronounced the jiiizhor the teme perature," "Tnis (cooked flavor) is left permae nently in milk exposed to about 170°”, for 15 minutes, Mxrosure to 170° F., in a closed vessel fol- lowed by imnediate cooling is the highest tenperature that may be used without leaving a cooked taste, "an minutes at 160° is safe, wad j}-« TALIM IV, (Continued). AU THO RS GUAT ME WS Aikman (f)rccccccccccccee "659 6, (14997, ) for 2) minutes (a) (0) (c) (d) (e) (f) induces a cooked flavor but this disappears on cooling. 70°R, (158°F ,) permanent chanze in taste, "filk and Its troducts," vy ‘ing. *“Prineinies and lYractice of -uttermakinz,"” by Vaolay and Larsen. "Market Dairying 2nd “ilk Froducts,” voy “Michels, "The “ilk Q@aestion,"” by Rosenan. “Pure Hilk and the fublie Nealth," by “ard. "“ilk its Nature end Composition,” by ‘iken,. A® people diffcr widely in their acility to cetect this cooked flavor in pasteurized milk, it sceccnes excecdinge iy a@iffieult to determine cefinitely at just «not point this fjavor is fir:t detcctcd, Again, sous rwitlorities affirm that milk heated in close: veesels has a much icse );ronounde ed flnvor than has ailk heated in open vessels, The following experiment, in which tests to determine the creaning ability, distinctness of crean line, and flae vor of milk -fter resteurication at varying tcnrerstures end with varving perioia of exrosire, =c8 gnje vy the writer in this “ilk plent with the following intereatinzg rcsultss Several ssunles of nilk contained in hsltepint Cote tres were hested, each to the teuperature deaired for it, oy imacrsing in hot vater kezt to the desired tenp-rature by a ane flame. After each sanple had seen exrosed to its desired teanerature for a given tine, it zas taken out of the Bath and ccrefully phaced in crine, where it “ag lett until cooled to 1. tenmrerature of 50° ¥, or lower, 10 a second test, some bottles were subnitte’ to the rapid cooling 332 In the first cnse@, while othsra were cooled elowly ty allovinz them to renain one an? oneehalf hour theresbout in room tenrerature ant after that by nlaains then in brine, ‘tach sannle of both tests, after being thoroughly cooled, wns joured into 8 100 @.0,. crsatuated ecytinier and tested for the sbove qualities after reanining in the refriverator tventyefour hours. “able V, is desianed to siiov the effect of high on @ a Je tenpernture and length of ex,.osure on the cressing abllity and flavor of nnsteurized milk, while Table Vi, siiows the average result ot the de-zree of rasidlty of cooling usoa these suae cumlities cf r:igsteurized ailk, see Tables V and VI, lo, of ste Sample wh she og 3 1 $7 2 : 3 : 4, : 5 3 6. $ f° 3 9 : _ 3 "he abov for ench. Gubdie een Fu 3.6, Oe of $s Saviple 3 3} ~ | 1 gf: 2 3 3 : 4. ? SO. 8 86&)~«6ght 6 3 2... % IJteated, triala co 109 eubic ‘723 3.7. before ru aa 2 me Resultea, As shown in Table VY, samples 2 hid ne effect upon tne creniing avility or cookeil flivor in milk. Sample 3} had the 3light cffect of sreventing the rising of aream out thore was no difference in distinctness and in flavor or taste, Sanaples 4 and 5 acre -ffected in distinetn-s: of Crea line and shoved iw snallow crean layer, tut no cooked Tlavoyr was develoved, In aample 6 the milk waa affected srastly in anount of erean and alightiy in ‘distinctness of the cream line, but no cooked flavor or tiste wis Pecoznized, In sanole 7 the cooked flxvor wos slightly teveloned in the mil« but otner conditions vere about the sane a9 those in anmple 6, In sanple & and 9 the creat line was destroyed entirely; while cooked flovor was developed alicthtly in sampe le 8 and arkedly in 9, Aga shown in Table VI, sample 2, the milk gis not affected as regards creaning mwality nor in flavor or taste, Sample 3 showed an anvarent decrease in the amount of Orean, but no effect on distinctness nor in flavor or taste, was notioceadle, In sample 4 the nilk was affected marke@ly as regards Sreanin,s ability, slizhtly as regards distinotacss, but not st 211 as reznrds flavor or taste, wa 2Bae In sample 5 the 2ilk was affeoted slijzitly more thn in sanple 4 in all these respects, in gam le G the milk was affceted liarescly in creasing quality and in distinctness, and sli-gd:tly in flavor, In sauple 7? the wilk «as so effectca in cvery rese yert os to ve easily deteoted aga herted milk, Couclugions, The investigation here reported is ;rovugoly not sufficlently authorit=tive to warrant the drowins of abwdlue tely definite conclusions, it is evident, liowever, that the creaning quality and cooxed :luavor of pastevrized milk «sre influenced ty varicus factors. "he princinal of thes: face tors 1763 (1) the teapernture to which the 1ilk is heated (2) The tine during which milk is «-x:coaet to the hizh temverature (3) The amount of asitrtion to whieh the milk is suujected, especially when 4+ hich temperature, (4) “he ranidity of cooling after heating (5) “he clarification of the milk before vaiteue rization, reasoning from the reault of the investigation of the practioal olarification and nasteurization of ilk as rexirds Lt creaming yuallty ond flavor, as well ss from the partioular experiment here conducted, we are led to the ~=290- follwwing conclusicns regarding the effect whicn this clari-e fication and rvasteurization has u-on the viesicl. or tangible quality of milk; First, a comparison of the result of the sediment test on clarifies anc original raw milk respectively Siiows that this clarification ty means of centrifuznl force is anatrumentnl in resasvinz the gre:ter nurt of the dirt and sediment to be found in original raw milk; seecni, it is nossible to rasteurize ilk vy heating it to a tenpcrature of 1409Y, and exposing it to this tenverature for tventy minutes, then raniadly cooling it to . tanporsture of 50° P. or telow, without any undesirable effect an the vAaiity of the 111k under considerationbeing noticcable. ‘io7, acocore Ging to themajority of bacteriologists the henting and cooling of milk within these teaueratures are j.ite suffie cient for bactericidal cfficiency. If, howcver, aiik is hentei during the pasteurization process at a tenperature higher than 140° ¥,, or if it is exposed while “+t this tem. rcrature for a onzer period than twenty minutes, it will be affected in crenming ability, or in flavor, or, 7s sonetines havens, in both. [t is veli to note, however, ‘ilint the exe cess of teaperature avove 1409 ¥, affects this creating qualie ty far more than dces the excess exposure. ‘gain the rapidie ty in cooling is néecessasry both for hygienic reasoi1s and for the nrevention of cookel flavor or taste. “his ravidity of cooling, .iowever, does not materially affect the creaming ability of the milk, ~-39- Agitation of the milk, especially when this milk isa rat n high temperceture, hos « distinctly noticeable effect upon the creom line. whe greater the eszzcunt o% this agitation the leaga the visible amcunt of cream, ‘his can be explained vy the preeence of lumps cf lLutterfat seen floating on the surface of the milk that has been go sgitated «fter it is cooled. An inveatisznator exnerinenting along this line dise covered that as the sveed of the agitnutor wiieh kent the silk in motion was retuced these tunsa of tutterfat shoved a tene deney to disanpear until when this sneed reached s certain minimom they disanneared entirely, It has also teen discovered that the sgitation caused by centrifugal force in the clarification of milk heate ed to an extremely high temtcraturé also sffected the creame inz quality. It did this first by separating the globules of butterfat fron the milk, then causing these globules to rus together, thus forming luaps of butterfat that float on the surface of the milk, Again, it has been observed that milk heated in closed veseels does not form any pellicle even when heated te the boiling roint; while wilk ex.oaed to the open air during tie preceas of heating alvays shows a péllicle on ite surface,- a pelitole that rearpenra if removed by skiauming. This pellicie, it would, therefore, scem, is mainly due to the evavoration of the surfsce layer of the milk, Toe 3 1293 03169 2001