38 BUTTER-MAKING. 



The great viscosity of thick and cold cream has been 

 encountered by most butter-makers when attempts have 

 been made to churn cream under such conditions. It adheres 

 to the inside of the churn and does not agitate. It simply 

 rotates with the churn. Cream that is cold and thick 

 whips more easily than thin and warm cream. The viscosity 

 is so great that the air incorporated cannot escape so easily. 

 In ice-cream making, a greater yield is obtained by using 

 cold and thick cream. The air, when once incorporated, 

 cannot easily escape, owing to the great viscosity of such 

 cream. 



Specific Heat of Milk. — The specific heat of milk is less 

 than that of water; that is, it requires less heat to warm a 

 definite amount of milk to a certain temperature than it does 

 to heat the same quantity of water to the same temperature. 

 It also takes less ice to cool the same volume of milk to a cer- 

 tain temperature than it does to cool the same quantity of 

 water to the same temperature. The specific heat of milk 

 is, according to Fjord, .94. The specific heat of cream is 

 about .7. It varies according to the percentage of fat in the 

 cream. The specific heat of butter is about .4. From these 

 figures it will be seen that it takes less heat to warm milk, 

 cream, and butter, and less cold to cool the same substances, 

 than it does to heat and cool water; but it takes a longer time 

 to heat or to cool milk, cream, and butter; that is, the milk, 

 cream, and butter are not as rapid conductors of heat and 

 cold as is water. 



The maximum density of milk is not, like water, at 4° C. 

 but at about .3° C. The boihng-point of milk is a trifle higher 

 and the freezing-point a trifle lower than that of water. 



Effect of High Heating (i8o° and above) on Properties of 

 Milk. — The chief effects of heat upon milk may be summarized 

 in the following headings : 



(1) It destroys nearly all germs present in the milk. 



(2) It diminishes the viscosity, or body. 



(3) It drives off gases 



