Temperature of Churning. 141 



tending to keep them apart. The more viscous the 

 milk, then, the greater the difficulty with which it 

 will churn. 



The ripeness of the cream. — The ripeness of the 

 cream affects the churning, largely because of its 

 effect upon the viscosity of the milk. The produc- 

 tion of lactic acid in milk always has the tendency 

 to render it less viscous, and sour milk or cream, 

 therefore, will churn more readily than sweet for 

 this reason. The viscosity of the milk must be 

 distinguished from the thickness of the milk, due 

 to the coagulation of the casein. Souring of the 

 milk renders it less viscous, but at the same time 

 by coagulating the casein renders it thicker and 

 less fluid. 



The temperature. — The temperature is the most im- 

 portant condition affecting churning. Whether the 

 particles of fat shall unite as they pass by one 

 another when the liquid is in motion, dej^ends very 

 largely upon their temperature and degree of plas- 

 ticity. If the temperature is too low, the globules 

 of fat are so hard that when they hit one another 

 they do not stick together. If, on the other hand, 

 the temperature is too high, the effect of agita- 

 ting the globules of fat is, instead of causing them 

 to unite, to break them up into still smaller glob- 

 ules, and so render the emulsion more permanent. 

 The range of temperature through which the parti- 

 cles of fat may be made to unite is considerable. 

 The extreme limits may be placed at from 46° to 

 80° F. But while butter may be churned from 



