PROPERTIES OF MILK 11 
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 Hol- 
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 
