20 Milk and Its Products. 
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, some- 
what less than eight per cent of the whole. The 
chief normal volatile fats are butyrin, caprin, caproin, 
eaprilin and rutin. 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. 
The volatile fats that are derived directly from 
the food may give either desirable or undesirable 
flavors to the milk. Thus we esteem the character- 
istic flavors due to the grasses, clover and like fodder; 
on the other hand, the stronger flavors of garlic, 
onions, turnips, cabbage, ete., give to the milk an 
undesirable character. 
The presence of these undesirable flavors in milk 
is often a source Mfitizad BOORrodevd of annoyance, but 
