Contamination of Milk. 45 



48. Aeration. Practical experience has long demon- 

 strated the advantage of aerating the milk as soon after 

 milking as possible. This is accomplished in a variety 

 of ways. In some cases, air is forced into the milk; in 

 others, the milk is allowed to distribute itself in a thin 

 sheet over a broad surface and fall some distance so that 

 it is brought intimately in contact with the air. The 

 benefit claimed for aeration is that foul odors and gases 

 which may be present in the milk are thus allowed to 

 escape by bringing the finely divided milk into contact 

 with the air. As ordinarily practiced, aeration is usually 

 combined with cooling, and it is noteworthy that the 

 most effective aerators are those that cool simultane- 

 ously. Under these conditions, the keeping quality of 

 the milk is increased, but where milk is simply aerated 

 without cooling, no material benefit in keeping quality 

 is observed. A satisfactory scientific explanation of the 

 advantages of aeration has not yet been made. It is dif- 

 ficult to see how the process can have any effect on the 

 bacterial life in the milk. Its influence, undoubtedly, is 

 on the odors directly absorbed by the milk. 



49. Distinction between bacterial and non-bac- 

 terial defects in milk. In fresh milk it is relatively 

 easy to distinguish between taints caused by the opera- 

 tion of external biological forces and those due to direct 

 absorption. 



If the taint grows more pronounced as the age of the 

 milk increases, it is probably due to the living organisms, 

 as the taint- producing bacteria usually gain an entrance 

 after the milk is drawn from the cow, and require a cer- 

 tain period of incubation before undesirable products are 

 formed. Taints due to errors in feeding are more pro- 

 nounced when the milk is first drawn. 



