coolijstg hot-bottled pasteurized milk. 



27 



Table I. — Bacterial groivih in milk during a quick and slow cooling to 45° F., followed 

 by holding for 6 hours at warm temperatures (bacteria in 1 c. c). 





Sample No. 





1 



2 



3 



4 



5 



6 



7 



8 



9 



10 





95,000 



176, 000 



176,000 



97, 500 



97. 5on 





450,000 





985,000 



38, 000 









Milk cooled quickly: 



Directly after pasteuriza- 

 tion 



600 

 1,000 



1,870 

 '2,050 



5, 750 

 1,320 



1,180 

 5,800 



1,570 

 12,370 



8,400 

 1,220 



5,520 

 6,100 



5,900 



5,900 



22,900 

 16,600 



890 

 1,700 



4,800 

 2,500 



8,300 

 8,900 



2 9, 600 

 7,500 



9, 800 

 2 8,900 



5,500 



After IS hours held at 45° F. 



5,200 



Sample then placed for 6 

 hours at S6° F 



6,600 

 5,900 



5,900 

 5,900 



2 5, 200 



Milk cooled slowly: 



Directly after pasteuriza- 

 tion." 



860 

 500 



21, 800 

 12, 300 



890 

 2,200 



5,400 

 715 



0,500 



Cooled slowly at room 

 temperature for 4 hours 

 and placed for 14 hours 

 in refrigerator at 45° F . . 



5,200 



Then placed for 6 hours at 

 86° F 



3,700 



3,700 



2 5, 300 















I Held at 45° F. for 21 hours, in place of 18 hours. 



2 Held at 75° F., instead of 86° F. 



As may be seen iii Table I, bacterial counts were made on each 

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

 IS-hour cooling period, and agam after the milk had been at room 

 temperature for six hours. The results obtained showed that there 

 was no more mcrease 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 num- 

 bers, even after milk cooled by both processes had been removed, 

 after 18 hours' cooling, and allowed to stand for 6 hours. 



The various counts from the 10 samples are averaged in Table II, 

 in order to show more plainly the effect of the two systems of cooling 

 on the bacterial numbers in milk. 



Table II. — Summary of results from Table I. 



Milk and stage of cooling process. 



Average 

 bacteria 

 per c.c. 



Cooled quickly: 



Directly after pasteurization 



After 18 hours in refrigerator , 



Taken from refrigerator and held 6 hours at temperatures from 75° to 86° F 



Cooled slowly: 



Directly after pasteurization 



Coole^l slowly at room temperature for 4 hours and held in refrigerator for 14 hours at 45° F 



Taken from refrigerator and held for 6 hours at temperatiu:es from 75° to 86° F 



Raw milk 



5, 823 

 5,040 

 0,908 



5,729 



4,678 



.5, .583 



264,375 



It wUl be seen in this table that the average bacterial counts of 

 milk cooled slowly, made at difTorent times, are even lower than those 

 of milk cooled quickly. WJiile this differern'o is p()ssi])ly an experi- 

 mental error, it is evident that bacterial growth in the pasteurized 

 milk was not increased by tlie slow-cooling jji-ocess. 



