164 



MANUAL OF MILK PRODUCTS 



particles of dirt in it. Its keeping quality is not usually im- 

 proved by this operation because the bacteria which control 

 the keeping quality are very minute and will pass freely 



through any strainer which 

 will allow the passage of the 

 fat globules (see Fig. 41). 

 Aeration. 



This is the process of ex- 

 posing milk to the air in 

 order to get rid of any odors 

 which it may contain. Milk 

 *p %^M^M^CJ W^ is aerated by allowing it to 



f <IP> €/ fnO? run over ^ e sur ^ ace °f the 



aerator in a thin film. In 



this way, any foreign odors 



existing in the milk, in the 



Fig. 41. — Appearance of milk under form of gases, are allowed to 



escape into the air. Normal 

 milk does not contain any 

 odors which need to be removed, but if the cows have 

 eaten certain strong-smelling feeds or the milk has absorbed 

 foreign odors from the stable air, it may be desirable to aerate 

 it. When milk is produced under proper conditions and 

 cooled promptly, it will have no undesirable odors. This is 

 shown by the fact that some of the highest quality milk 

 is taken directly from the cow, bottled, and submerged in 

 ice water with the least possible exposure to the air. The 

 common belief that aeration improves the quality of milk 

 is probably due to the fact that most aerators also cool the 

 milk, and the beneficial results are due to the cooling rather 

 than to the aeration. If an aerator is used, great care should 

 be taken to have the atmosphere free from odors or dust. 

 Otherwise, the final quality of the milk may be worse than the 

 first. 



the microscope, showing relative size of 

 fat globules and bacteria 



