MILK AND ITS PRODUCTS 127 



Butyric acid is soluble and is a liquid which solidifies 

 at 2 F. and melts again at 28 F. 



Insoluble Fats. A study of these fats is essential in 

 elucidating the variability of the churning temperature 

 of cream. As a rule this is largely determined by the 

 relative amounts of hard and soft fats present in butter 

 fat. Other conditions the same, the harder the fat the 

 higher the churning temperature. Scarcely any two milks 

 contain exactly the same relative amounts of hard and 

 soft fats, and it is for this reason that the churning tem- 

 perature is such a variable one. 



The relative amounts of hard and soft fats are influ- 

 enced by: 



1. Breeds. 



2. Feeds. 



3. Period of lactation. 



4. Individuality of cows. 



The butter fat of Jerseys is harder than that of Hoi- 

 steins and, therefore, requires a relatively high churning 

 temperature, the difference being about six degrees. 



Feeds have an important influence upon the character 

 of the butter fat. Cotton seed meal and bran, for example, 

 materially increase the percentage of hard fats. Gluten 

 feeds and linseed meal, on the other hand, produce a soft 

 butter fat. 



With the advance of the period of lactation the per- 

 centage of hard fat increases. This chemical change, to- 

 gether with the physical change which butter fat under- 

 goes, makes churning difficult in the late period of lac- 

 tation. 



The individuality of the cow also to a great extent 

 influences the character of the butter fat. It is inherent 



