266 CHURNING 



CHAPTER X. 

 CHURNING. 



Object of Churning. The object of churning is to separate 

 the butterfat from the caseous and serous parts of the milk or 

 cream, to make butter. This is accomplished by the formation 

 of butter granules. 



Philosophy of Churning. The formation of butter granules 

 is brought about by the crystallization or solidification of the 

 fat in the fat globules and by coalescence of the wholly or 

 partly solidified fat globules into butter granules. 



Milk and Cream an Emulsion. In freshly drawn milk the 

 fat is present in the form of minute globules of liquid fat. These 

 fat globules are emulsified in a watery mixture of hydrated col- 

 loid the skim milk. An emulsion, in this case, is a mixture 

 of two liquids which are insoluble in each other, where one is 

 suspended in the other in the form of minute globules. Milk 

 then represents an emulsion of fat-in-skim milk, the fat rep- 

 resenting the divided or dispersed phase, and the skim milk 

 the continuous or dispersing phase of the emulsion. As long 

 as this emulsion remains intact, there can be no formation of 

 butter granules. Butter does not form. 



The establishment of this emulsion of fat-in-skim milk is 

 the direct result of the process of milk secretion. When milk 

 is secreted, nature places the fat, \vhich is liberated by the 

 metabolic activity of the cells which line the alveoli, into the 

 skim milk in the form of very finely divided particles. 



Fischer and Hooker 1 who made an extensive study of fatty 

 secretions and fatty emulsions, considering the phenomena of 

 milk secretion from the standpoint of the pathologist, speak 

 of the secretion of butterfat as a fatty degeneration of the cells 

 in the alveoli. "The originally cubical cells w r hich make up 

 the alveoli of an active mammary gland become richer in water 

 and filled with granules (cloudy swelling), while the fat in 

 the cells runs together into more readily visible droplets (fatty 

 degeneration). When this process of cloudy swelling with fat 



1 Martin H. Fischer and Marion O. Hooker, Fats and Fatty Degeneration, 

 1917. 



