Milk and Its Products. 283 



of being sweet and of keeping better than the product from other 

 processes of skimming. 



Butter. When cream or milk is agitated for some time, the 

 fat globules coalesce and butter separates out in irregular masses. 

 While these masses are not continuous fat, very few of the 

 original globules remain. The spherical globules visible in but- 

 ter under the microscope consist of minute drops of butter-milk 

 or water, enclosed in the fat. 



Churning is a mechanical process. The fat globules collide, 

 adhere, and the large irregular masses thus formed become cen- 

 ters of growth, to which other fat globules adhere. Portions of 

 the aqueous liquid, butter-milk, are enclosed in the masses of fat. 

 During the "working" of the butter, the butter-milk is partly 

 pressed out. For butter to be of good quality, it must possess 

 a certain texture and grain and be neither hard nor greasy. This 

 desirable result can only be attained by careful churning at a 

 favorable temperature. If the temperature of the cream is too 

 low the butter will be long in coming and will be hard in texture. 

 If the temperature is too high, the butter will come very speed- 

 ily, but the product will be greasy and destitute of grain. No 

 temperature can be fixed as the best at which churning should 

 always take place. The proportion of solid and liquid fats in 

 the milk varies somewhat with the breed and feed of the cow, 

 and this necessitates a change in the temperature. From 45 to 

 65 F. is the greatest range usually employed and, in most cases 

 from 50 to 60 F. is chosen. "Kipened" or sour cream must 

 be churned at a higher temperature than that required for sweet 

 cream. The exact temperature most suitable for churning may 

 be ascertained, by recording every day the temperature employed, 

 the length of time occupied in churning and the character of the 

 product. When this is done the experience gained can be used 

 in selecting the most suitable temperature. 



The temperature may rise during churning, work being con- 

 verted into heat. This causes an expansion of the air in the 

 churn. In addition, the carbon-dioxide in solution in the serum 



