122 Milk and Its Products 



who discovered and used the process in controlling 

 the fermentations of wine and beer. It differs from 

 sterilization only in the degree of heat used, and, in 

 fact, may be properly called an incomplete or partial 

 sterilization. The destructive effect of heat upon 

 germ life depends both upon .the degree of heat and 

 the length of time to which the germs are exposed. 

 A large number of germs are killed at temperatures 

 from 133 to 140 F., while others are killed at tem- 

 peratures varying from 150 to 165 F. These latter 

 temperatures include the germs of all of the ordinary 

 ferments and most of the germs of specific diseases, 

 including that of the tubercle bacillus. Since the 

 tubercle bacillus is the disease germ most likely to be 

 present, milk is ordinarily considered to be safe from 

 disease germs when it has been pasteurized at a tem- 

 perature sufficiently high to destroy it. This is a 

 temperature of 149 F. for thirty minutes, a tem- 

 perature of 155 F. for fifteen minutes, or a tempera- 

 ture of 167 F. for ten minutes, and these temperatures 

 have come to be looked upon as standard pasteuriz- 

 ing temperatures. Milk may be heated to 165 F., 

 if quickly cooled afterwards, without developing a 

 boiled taste ; so that it is possible that milk be 

 rendered safe from the germs of disease and free 

 from the ordinary germs of fermentation without 

 developing in it a boiled taste. But in order to 

 pasteurize milk safely, it is necessary that means 

 should be provided for cooling rapidly from the 

 pasteurizing temperatures to 50 F. or below. 



Milk carefully pasteurized, as above described, will 



