CHAPTER XXV. 



COOLING AND AERATION OF MILK AND CREAM. 



Importance of Low Temperature. Milk always con- 

 tains bacteria no matter how cleanly the conditions under 

 which it is drawn. At ordinary temperatures these bac- 

 teria increase with marvelous rapidity; at low tempera- 

 tures their growth practically ceases. The effect of tem- 

 perature on bacterial development is graphically shown 

 in Fig. 57. 



Fig. 57. Relation of temperature to bacterial growth. 



a represents a single bacterium; b, its progeny in twenty-four hours in 

 milk kept at 50 F.; c, its progeny in twenty-four hours in milk kept at 70 F. 

 (Bui. 26, Storrs, Conn.) 



At a temperature of 50 F. the bacteria multiplied five 

 times; at 70 F. they multiplied seven hundred and fifty 

 times. 



Roughly speaking, at 98 F. bacteria multiply one hun- 



205 



