CHAPTER VII 



Methods of Testing the Acidity of Milk and Milk 

 Products 



It is often necessary to know how much acid is 

 present in milk, cream, whey, etc. The amount of 

 acid in milk may be a suggestive indication of the 

 age of milk and of its care. In butter-making, the 

 uniformity of the product depends largely upon the 

 ripening of cream, which can be well controlled only 

 by knowing its acidity. In cheese-making, it is at 

 times important to know whether milk contains too 

 much acid and it is also quite essential to have some 

 knowledge of the amount of acid present in the milk 

 and whey at different stages of the operation. 



THE CAUSES OF ACIDITY IN MILK AND ITS 

 PRODUCTS 



We may distinguish two kinds of acidity in milk 

 and its products: (i) Apparent acidity, and (c) acid- 

 ity due to lactic acid. The apparent acidity is due to 

 the presence in normal milk of casein and acid phos- 

 phates, which have the power, like free acids, of neu- 

 tralizing alkalis. This apparent acidity in fresh milk 

 is about .07 or .08 per cent, on the average. It varies 

 with different conditions, increasing, for instance, with 

 advance of lactation. 



Acidity due to lactic acid is formed in milk after it 

 is drawn, and is caused by the action of certain forms 



96 



