CHAPTER V. 

 FERMENTATIONS OF MILK. 



A large number of kinds of bacteria enter the milk 

 during its production on the farm. From the udder, 

 the exterior of the animal, the manure, the barn-dust, 

 utensils, and milker come many kinds of bacteria, 

 yoasts, and molds. Many of these micro-organisms can 

 grow in milk. 



Composition of milk. Milk is composed of about 87 

 p*.T cent water, in which is dissolved about 5 per cent 

 of milk sugar (lactose), various salts, as common salt, 

 calcium phosphate, etc, and 0.5 per cent of albumen, a 

 substance resembling the white of egg. In suspension 

 in the milk there is 2-4 per cent of casein, the substance 

 that, gives to skim milk its whitish color and makes up 

 the larger part of the curd in sour milk. 



Milk is a perfect food for animals and also for most 

 bacteria. The different kinds when growing in milk 

 use the various substances it contains as food. From 

 these they produce many products which alter the milk 

 as to appearance, odor, and taste. The various changes 

 produced are known as the fermentations of milk, and 

 are designated by the name of the most important by- 

 product formed. Thus, the souring of milk is called 

 the lactic acid fermentation, because lactic acid is the 

 most prominent substance in this change. 



Souring of milk. The souring or acid fermentation 

 of milk is so common a change that it is looked upon as 



