CHAPTER IV. 



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. 4. 



or ^^ 



I'ig. 4. — Relation of temperature to bacterial growth. 



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

 milk kept at 60° 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- 



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