260 STATE BOARD OF, AGRICULTURE. 



oxygen, and, if the milk is not cooled, a temperature most suitable for the development 

 of germ life is present — conditions in short which favor harmful fermentations. This 

 is why there are recorded so many cases of poisoning as due to the, improper care of the 

 milk, eliminating the factor filth, a common evil. 



Many dairymen have studied the action of aeration upon butter and cheese-making 

 but without any positive results favorable or unfavorable. The results in the light of 

 our experiments can be explained by a failure to recognize a difference between 

 perfectly aerated and unaerated milk. The milk employed by these experimenters will 

 show no great increase in the oxygen supply between that which was considered 

 aerated and that considered non-aerated. If a wide difference could be established there 

 would probably result appreciable differences in the products mentioned due to the 

 influence the oxygen would have upon the ripening of cream and cheese, and the 

 keeping qualities of the butter and cheese. These suggestions are tentative and subject 

 to experimental evidence. 



It has been hinted that aeration has caused an inciease in the quantities of butter 

 and cheese. Perhaps oxidation has some influence upon the fat and casein but thus 

 far I have been unable to demonstrate it. In my work I have obtained marked peptoniz- 

 ing action by germs within twenty-four hours under an exclusion of oxygen, but this is 

 not common. There were two samples of milk which were under conditions which 

 excluded oxygen: these clarified completely in twelve hours in the incubator, that is. 

 all the casein dissolved ; usually, moreover, the milk loppered from lactic acid fermenta- 

 tion. If there is any difference therefore in the quantities of cheese obtained it is 

 due largely to proteolytic fermentation induced by bacteria which might be favored by 

 the exclusion of oxygen. 



Our experiments further show that the number of bacteria is not reduced by aeration 

 as has sometimes been suggested, and that the germicidal action of milk is not effected. 



It has long been known that animal odors and taints may be removed by aeration. 

 Proper aeration will do it; however aeration and cooling must not be confounded in 

 this matter. Cooling apparently removes odors and taints but such disappearances are 

 due to the chilling of the milk under which condition the milk gives up the volatile 

 substances with reluctance, doubtless owing to the reduced power of volatility of the 

 substances themselves when cold. When such odors and taints are removed by aeration 

 the removal is permanent unless they are generated by bacteria which continue to grow 

 after aeration. Odors and taints may be due to any one of the following causes: — 



1. Absorption of gases from the air by the milk. 



2. Physiological processes of the cow. 



3. Disease processes of the cow. 



4. Bacterial growth in the milk. 



5. Introduction of odoriferous substances into the milk. 



Odors in the air emanate from fermentations, foods, etc.; aromatic food substances 

 are likely to pass through the body and be secreted in the milk; a high temperature in 

 an animal is likely to reveal itself in the milk; many taints arise from bacterial 

 development in the milk; and frequently sufficient filth gets into the milk to give 

 it a distinct flavor — all of these or any one of these causes may be the immediate 

 producer of odor or taint. 



How aeration should be conducted is a matter of considerable importance, conse- 

 quently we have added a few suggestions: — 



1. Aeration should be conducted at body temperature. 



2. Aeration should be carried out over the most extensive surface possible and as 

 slowly as possible. 



3. Aeration should take place only in a pure atmosphere. 



4. Aeration is best accomplished immediately after milking. 



5. Aeration should precede cooling. 



6. Aeration and cooling simultaneously conducted cannot yield the most satisfactory 

 results. 



