COMPOSITION OF MILK. 11 



It was previously stated that little is known concerning 

 the way in which the fatty acids are combined with glycerine 

 in the milk; but, for the sake of convenience, the fats will be 

 referred to as if they exist as separate glycerides of fat. 



The terms " Volatile " and " Non-volatile " are apphed 

 to the glycerides of fat, or to the fats as they exist in butter. 

 Strictly speaking, this is not proper, as they do not assume 

 the volatile characteristics until the glycerine separates from 

 the fatty acids; it is only then that the latter becomes volatile. 



Volatile Fats. — The first group, or the volatile fats, include 

 butyrin, caproin, caprylin, caprin, and laurin. Butyrin is the 

 one present in the largest proportion. Laurin and caprin are 

 partially non-volatile. Butyrin is the most important fat 

 belonging to the volatile group. It is the most important 

 quantitatively, and also qualitatively. So far as is known, 

 butyrin is the least stable of any of the butter-fats. Under 

 normal conditions, so long as the fatty acid remains in com- 

 bination with the glycerol, it is not volatile nor soluble in 

 water but as soon as separation takes place, due to the action 

 of micro-organisms, or to the effect of light and air, then it 

 becomes volatile, and escapes in the form of gas. According 

 to the mass of evidence, these factors are the chief causes of 

 rancidity in butter. 



It is also claimed that these volatile fats have the special 

 properties of absorbing odors and gases to a greater extent 

 than any of the other fats. This absorption takes place when 

 fat comes into contact with the undesirable taints. For this 

 reason it is essential that milk, cream, or butter be kept away 

 from any foreign undesirable odors. These undesirable taints 

 may also be imparted to the fat before the milk is drawn. 

 If the cow is fed on undesirable food such as turnips, onions, 

 garlic, etc., the milk from the cow assumes undesirable char- 

 acteristic flavors, which can- easily be recognized in the finished 

 product. On the other hand, such foods as well-cured sweet- 

 clover hay, and bran, seem to impart desirable flavors to 

 milk and butter. 



