166 



MANUAL OF MILK PRODUCTS 



milk. The effect of temperature on the growth of the bacteria 

 and the keeping quality of the milk is shown by results ob- 

 tained by dividing a lot of milk into six parts, each being held 

 at a constant temperature for twelve hours. At the end of 

 this time, the bacteria count was determined for each lot. 

 The samples were then all placed at a temperature of 70° and 

 held until they curdled. 



Effect of Temperature on the Development of Bacteria and 



the Keeping Quality of Milk l 



Temperature held for 12 Hours 



Bacteria per C.C. 



at End op 12 



Hours 



Hours to Cur- 

 dling at 70° F. 



40° F 



4,000 



9,000 



18,000 



38,000 



453,000 



8,800,000 



55,300,000 



75 



45° F. ... 



75 



50° F 



72 



55° F. 



49 



60° F 



43 



70° F 



32 



80° F 



28 







The fresh milk showed a bacteria count of 5000 to 

 a cubic centimeter, and when held at a constant temper- 

 ature of 70° it curdled in fifty-two hours. It should be 

 noted that these samples were held at the different tem- 

 peratures for twelve hours only, and that the effect on 

 the keeping quality is the result of the special temperature 

 of this twelve-hour period, and not the entire period to the 

 time of curdling. Prompt cooling to a low temperature 

 is of vital importance in the handling of milk which is to be 

 held for some hours before being consumed; and the longer 

 the time between production and consumption, the more 

 important this factor becomes. It must also be borne in 

 mind that cooling does not kill the bacteria, and if the milk is 

 allowed to warm up, they will at once become active. In order 

 1 New York Dept. of Agr. Circular 10. 



