Temperature of Churning 211 
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, depends 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 
