38 PROPERTIES OE MILK 



lure and fat cuntcnt. Su far as understood, the lower the tem- 

 perature, the KfL'ater the viscosity. Develojmient of acid, and 

 high temperature lessen the viscosity of milk. Pasteurized milk 

 or cream is less viscous than the same milk or cream unpasteur- 

 ized. This lack of body can again be restored by adding a httle 

 viscogen, as recommended by Babcock and Russell. It is not 

 advisable to use it, however, as it does not add materially to the 

 nutritive value of milk, but merely restores the body. 



The great viscosity of thick cold cream makes it difficult to 

 churn, as most butter-makers have discovered. It adheres 

 to the inside of the churn and simply rotates instead of being 

 agitated. Cream that is cold and thick whips more easily than 

 thin, warm cream, as the viscosity is so great that the air incor- 

 porated cannot escape so easily. In ice-cream making, for the 

 same reason, a greater yield is obtained by using cold, thick 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 certain temperature 

 than it does to cool the same quantity of water to the same tem- 

 perature. 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 reached, like that of 

 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 chiel effects ol heat upon milk may be summarized 

 in the following headings: 



