OCR Text |
Show jfib ORMILKv "M thu In tho early sixties of last century, whllo studying diseases of wine, Pasteur Pas-teur discovered that It was sufflclcnt to heat wino for n fow seconds nt a temperature of BO degrees to 00 do-grees do-grees C. In order to prevent souring. Later ho found thnt beer could bo like-wlso like-wlso preserved by heating to CO degrees de-grees to f5 degrees C. Tho application applica-tion of this process to various articles of food gavp rise to tho term "pasteurization." "pas-teurization." Pasteurization of milk consists In heating It for u short tlmo at a temperature below tho boiling point, and then rapidly chilling It Tho object In heating Is tho destruction destruc-tion of disease-producing germs, nnd If tho milk wero allowed to root slowly It would remain for a comparatively compara-tively long tlmo at 20 degrees to 37 degrees C, tho best tcmporaturo for the development of such bacteria and their 'poisonous products. Various temperatures and times havo bcon recommended rec-ommended for Pasteurization, ranging from CO degrees to 95 degrees C, and from a fow seconds to two hours. Tho term "pasteurized" Is accordingly Indefinite, In-definite, and should bo replaced In commorco by n plain label Indicating tho temperature, tho tlmo and the dato of heating. Tho two dominant factors fac-tors that appear to control tho temperature tem-perature and tlmo of pasteurization are the thermal death points of pathogenic patho-genic bacteria and tho thermal death points of milk ferments. Tho bacteria should bo killed and tho torments should remain unaffected. It may bo horo .noted that considerable experimental experi-mental difficulties surround tho determination deter-mination of tho thermal death points of both bacteria and ferments, and that concerning tho function of milk torments nothing Is definitely known. Pasteurized milk, then, merely means heated milk, and Is not nt all synonymous synony-mous with clean milk, pure milk or good milk. Pasteurization cannot ntono for filth, and cannot presorvo the best milk for any considerable length of tlmo. Pasteurization In practised prac-tised on a largo scale In tho cream-crlos cream-crlos of Europe and Amorlca. In Denmark Den-mark and (iormany It Is much In evidence, evi-dence, and it Is estimated that 25 per cent of tho total dally milk supplied to tho city of New Yotk Is pasteurized. pasteur-ized. In Denmark, threo different modifications of tho process are In operation: (1) Heating for times varying vary-ing from 15 minutes to ono hour at 85 degrees C. while tho milk flows through an appropriate pasteurizing apparatus, after which It Is Immediately Immedi-ately cooled; (2) heating for n longer tlmo In, sterilized vessels nt G5 degrees de-grees to SO degrees C, when tho vessels ves-sels aro sealed and quickly cooled; (3) heating from ono-qunrter hour to ono hour nt 05 degrees C. In a tank, after whtch tho milk passes througn a cooler Into tho vessel from which It Is sold. A largo number of machines havo been constructed for the .quick pasteurization of milk. In somo tho milk Is placed In n copper tank provided pro-vided with an Insulated steam Jacket. Tho tank contains rotating nrms by which tho milk Is thrown ngulnst the heated walls. Tho milk enters at the bottom nnd leaves at tho top. Dy regulating reg-ulating the quantity of milk admitted, tho rapidity of tho revolving nrms nnd tho amount of steam, tho milk may bo heated as desired. Wha'tever apparatus bo used, It should bo under the constant observation of a reliable superintendent, ensy to clean, and so constructed that tho entire quantity of milk, Including tho froth, can be equally heated to tho doslrod tempera' ture. Tho thermometer attached should bo specially testod, From tho pasteurizer tho milk Immediately passes to a cooler, which reduces tho temperature as rapidly and as much as possibly. Milk, presents the strnngo contrast of being tho most wholesome of nil foodstuffB, and at ttmos ono of tho most poisonous, It is tho most dim-cult dim-cult of all foods to presorvo nnd linn-dlo linn-dlo In a pure stnto, In that It Is an Ideal medium for tho cultivation of all classes of bacteria, Tho averago milk supplied to largo cities Is not a safo food. This Is duo to the Ignoranco and ludlffeicuco of thoso engaged In tho dairy business, to tho unclean and unhealthy cows used for producing milk, to ltn Insufficient cooling, to long transportation, to unnecessary and frequont handling, to lack of proper cleansing and sterilization of contalulng vessels and to Its frequent association with Infectious dlsoaso. Ilactorla enter milk Immediately It Is oxposod to tho atmosphoro. At the tlmo of milking this exposure Is grt'l.t-est. grt'l.t-est. While purhups It 1b Impossible to avoid wholly tho Introduction of bac-torla bac-torla during milking, If proper pro-cautions pro-cautions bo taken tho number Intro--Wni-iu.r; -liu lUunTuTJ "biffini." liae-" torla reach tho milk" from tho tnr.t, udder nnd body of tho cow, from tho hands, body and clothing 6t tho milker, milk-er, with the dust from tho atmosphere, from particles of oxcrement or litter which entor the pall nnd from tho pall itself. The action of these bacteria bac-teria may he considered bioadly as of I three types: (1) The large group of so-called lactic bacteria produces lac- tic acid from milk Bugar, which actjH it precipitates tho principal protein otB milk, causing tho well-known curdlinijB or souring. This always occurs whuB milk Is exposed (o tho air and kept at Htxs a tempornturo nbovo ten degrees C. Hj Thcso organisms ns n group are hare. H! less, as aro also tho products of thtlrHj growth. They, moreover, render geel Hj sorvlco by Inhibiting or crowding out Hj tho vory harmful putrefactive bacterli which so frequently reach milk from Bj excreta. Thcso non-spbrlng organlsai Hl aro killed by mo3t methods of pu'H1217 tourlzation, Whllo tho sporlng putrt H factlvo organisms nro not killed bj any mothod. It Is obvious, therefore, that a pasteurized milk contalnlni Bj putrcfactivo bacteria such as tho 0 jf acrogencs capsulatus or tho I). putrt b Ileus ot Ulenstock, Is In a much less vj protected condition than raw milk, (2) 1 Anothor group ot organisms product A butyrlo fermentation, also an acid change Theso grow best at a torn-pcraturo torn-pcraturo approaching that ot tho lis-man lis-man body, nnd produco spores which H' resist tho temperature of boiling wa, H ter for somo tlmo. Tho products ot their growth produco serious disturb- B ; nnco In tho Intostlnal tract of man, B j moro especially of children. Tat B j spores ot tho germs ot butyric ter B ! mentation are not. killed by pastcurt- B ' zatlon. (3) Several micro-organisms, B ' Including tho two mentioned In (1), B produco putrcfactivo fermentations B alkallno changes which proceed la B milk without Indications visible to the B naked eyo. Thcso spore-bearing or- B ganlsms nro not destroyed by pasteurl- B zatlon. Too frequently milk comes In B contact with organisms ot specific dls- B ease, o. g., tuberculosis, typhoid fover, B diphtheria, etc. Pasteurization for 20 B minutes at CO degrees to C5 degrees 0 B according to Rosennu, or 70 degreei jB to 80 degrees C. for a shorter period according to Jensen, will effectually destroy nil such organisms. Tho length of tlmo during which B milk will keep that Is, tho length ol H tlmo which must olapsa boforo sum B clent numbers of bacteria dovelop to B produco percoptlblo changes In It li a function of two factors, temperature and tho Initial number of bacteria present. Under ordinarily favorable pK conditions, tho number of bacteria In fB milk freshly, drawn from a healthy cow will vary between COO and 20,000 IK por cubic contlmeter. Milk can be produced by commercial mothods which will contnln less than C.000 bac-terla bac-terla per cubic centlmotcr. On the other hand, carelessly produced, the pB number may reach 500,000,000. Since BB most consumers consldor pasteurized BB milk as safe, It s'jould bo required, If BB tho process bo used, that It bo heated BB to n sufficiently high tompernturo to BB kill with certainty all dlseaso-pro- BB duclng germs. Pasteurization cer- BB talnly necessitates, a hotter modo of BB delivery of milk, but at best It 1b an BB expedient rather than nn Ideal method BB ot dealing with milk. No trustworthy BB conclusions can bo drawn concerning BJ tho effectiveness of pasteurization BB from tho bacterial content ot pasteup Bfl lzed milk cold In the retail market, as Bfl ono docs not know tho nature of the BB milk boforo pasteurization, how long Bfl It hnB beon kept, or tho tomporature H at which It has been kopt; and In this 'H connection It must over be remom- IB bored that toxic products unaffected H by heat are constantly being produced flfl In milk. Wo havo no method of deter H mining whother or not pasteurized BJ milk was dPmagcd before It wns heat BJ ed. whoreas tho kooplng quality and BJ bacterial content of raw milk furnish BJ good ovldonco ot Its real condition. |