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 boiling-point of milk is a trifle higher 
and the freezing-point a trifle lower than that of water. 
Effect of High Heating (180° 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. 
