PASTETJKIZING MILK. 



21 



Table 6. — Number of bacteria per cubic centimeter in pasteurised milk bottled, 

 hot, cooled quickly and slotvly, and subsequently held at room temperature. 



Method of cooling. 



Sample No. 



Aver- 

 age of 

 10 





1 



2 



3 



4 



5 



6 



7 



8 



9 



10 



sam- 

 ples. 



Bacteria in the raw milk 



Bottle No. 1, cooled quickly: 

 Directly after pasteur- 



95, 000 



600 



1,000 



176,000 



1,870 



i 2, 050 

 5,750 



1,320 



1,180 

 5,800 



176, 000 



1,570 



i 2, 370 

 8,400 



1,220 



5,520 

 6,100 



97, 500 

 5,900 



97,500 

 5,900 



22,900 

 16,600 



450,000 



890 



1,700 



4,800 

 2,500 



985,000 



8,300 



8,900 

 2 9, 600 



7,500 



9,800 

 2 8, 900 



38,000 



5,500 



5,200 

 2 5, 200 



6,500 



5,200 

 2 5, 300 



264,375 

 5,823 



After one-half hour in 

 ice water and 17£ 



5,040 





6,600 

 5,900 



5,900 

 5,900 



6, 90S 



BottleNo. 2,cooledslowly: 

 Directly after pasteur- 

 ization 



860 

 500 



21, 800 

 12,300 



890 

 2,200 



5,400 



715 



5,729 



After 4 hours at room 

 temperature and 14 

 hours at 45° F 



4,678 



After 6 hours at 86° F. . 



3,700 



3,700 



5,583 















1 Held at 45° F. for 21 hours in place of IS hours. 



2 Held at 75° F. instead of 86° F. 



As may be seen from Table 6, bacterial counts were made of the 

 raw milk on each bottle directly after pasteurization, at the end of 

 the 18-hour cooling period, and again after the milk had been at 

 room temperature for six hours. The bacterial results obtained 

 showed that there was no more increase in the pasteurized milk cooled 

 slowly than in similar milk cooled within half an hour and held at 

 low temperatures for 18 hours. Neither was there any difference in 

 the bacterial numbers even after milk cooled by both processes had 

 been removed, after 18 hours' cooling, and allowed to stand for six 

 hours. The various counts from 10 samples have been averaged and 

 are given in the last column in order to show more plainly the effect 

 of the two systems of cooling on the bacterial numbers in milk. It 

 will be seen that the average bacterial counts of the milk cooled 

 slowly are even lower than those of milk cooled quickly. While this 

 difference is probably an experimental error, it is evident that bac- 

 terial growth in the pasteurized milk was not increased by the slow- 

 cooling process. 



The writers do not wish to convey the idea that pasteurized milk 

 need not be cooled at all. The cooling of any milk is absolutely essen- 

 tial in order to restrain bacterial growth, and the fact should be 

 emphasized that the process of cooling pasteurized milk slowly does 

 not dismiss the cooling process but simply makes use of a slower 

 cooling process than is in use at present. 



In order to show, respectively, the effect on the bacterial content 

 of cooling quickly, cooling slowly, and not cooling to low tempera- 

 tures at all, three experiments were made. Milk was pasteurized in 

 bulk and three steamed and hot quart bottles were filled with the hot 

 milk. One bottle was cooled in iced water in half an hour to 50° F. 

 and refrigerated at 45° F. Another bottle was cooled in a blast of 

 air at room temperature for half an hour during which time the 



