8 BULLETIX 469, U. S. DEPARTMENT OF AGRICULTURE. 
on the farm. Beef and mutton fats, or tallows, as they were gen- 
erally known, were used in cooking to some extent in the form 
of "dripping" obtained from cooking meats, but found a much 
wider use for candle and soap making. Chicken fat was also used 
in a limited way. As the population began to concentrate in cities 
and towns, the introduction of central slaughterhouses and rendering 
plants made it possible to obtain both meat and fat separately in such 
ways as met individual requirements, and home rendering of fats 
quite generally disappeared except in rural regions. The increasing 
population created a demand which soon exceeded the available sup- 
ply obtained from slaughtered animals, and this made it necessary 
to seek additional sources of edible fats. Naturally, olive oil, used 
for food purposes in some parts of Europe and the Orient and less 
generally in the United States, suggested the possibility of the utili- 
zation of other vegetable fats, and as the methods of refining were 
improved cottonseed oil came to be very commonly used, and, to a 
less extent, coconut, peanut, and corn oils. At the present time there 
are also a number of vegetable fats on the market, some of which 
are simply refined and used alone or in admixture, while others have 
been treated by special processes designed to render them harder or 
otherwise changed in character. In the following pages general 
information is given regarding the nature, source, and use of some of 
the more important edible fats. - 
ANIMAL FATS. 
BUTTER. 
Butter is the most popular and widely used of all fats in the 
United States, it being estimated that from 17 to 18 pounds per 
capita are consumed yearly, most of it for table purposes. Its food 
value is due largely to the energy it furnishes, which is about 3,500 
calories per pound. It consists of the fat of milk, some water, and 
a little curd and added salt. Butter is of two kinds, salted 
and unsalted. Commercial butter contains approximately 82.5 per 
cent of fat, which consists chiefly of palmitin and olein with small 
amounts of myristin, butyrin,* and other glycerids of the fatty acids. 
The color varies considerably with the nature of the food materials 
eaten by the cow ; the yellow is deeper in summer when green food 
is eaten. It is a common practice to add vegetable coloring matter, 
especially during the winter months, to intensify the natural color. 
Since butter tends to deteriorate easily, care in its manufacture is 
necessary to secure a wholesome product with good keeping qualities. 
The milk from which the cream is separated should be free from 
disease-causing bacteria as well as from microorganisms which would 
produce undesirable flavors or odors in the butter. For this reason 
