20 Milk and Its Products 
determination of the specific gravity became of little 
value. Unscrupulous dairymen soon learned that 
water could be added to milk and fat or cream 
taken from it in such proportions that the specific 
gravity would remain the same as that of normal 
milk. 
The fats.—The fat of milk, or butter fat, as it 
is often called, is a mixture of a considerable number 
of separate and distinct fats, no less than six or 
eight being normal to milk, and a considerable fur- 
ther number may be present under various conditions. 
The fats in milk are of two kinds, volatile and non- 
volatile. To the former class belong the various 
normal essential oils that give to milk and butter 
their characteristic odors and flavors, and in addition 
to these normal fats there may be a large number 
of volatile oils that are present in the food of the 
cow, and that impart to the milk the characteristic 
flavors of such foods. 
The volatile fats.—The volatile fats make up only 
a small part of the total milk fat; in general, prob- 
ably about 15 per cent of the whole. The chief 
normal volatile fats are butyrin, caprin, caproin, 
caprilin and laurin. Of these, butyrin is in much 
the largest proportion and of much the greatest im- 
portance. It is the chief volatile fat of milk and 
butter, and to it are due in large part the character- 
istic flavors and aromas of milk and butter. Butyrin 
readily decomposes, forming butyric acid, which is the 
chief element in the rancid or “frowy” taste that 
butter acquires upon long standing. 
