2 BULLETIN 469, U. S. DEPARTMENT OF AGRICULTURE. 
of the nature and use of foods (some rich in fat) has been considered 
in other bulletins of this series, the present publication is concerned 
chiefly with the second group, or the added fats. For convenience 
the added fats may be subdivided into table and culinary fats. Table 
fats are those like butter and table oils, which are most commonly 
used as an accompaniment to food to secure a desired flavor or tex- 
ture, and culinary or cooking fats are those which are incorporated 
with other foods (as shortening) or used as a medium for cooking 
foods, as in frying. Economy in the use of the added fats involves 
the intelligent selection of the different kinds, so as to secure the sort 
best adapted for a particular purpose, and the careful use in the 
home of the fats selected. It is the purpose of this publication to 
consider briefly the nature of fats, their value in the diet, and their 
digestibility : to describe the great variety of table, and culinary fats 
on the market; and finally, to consider the economical selection and 
use of fats in the home. It is believed that such knowledge will prove 
helpful in buying and using fats to the best advantage. 
GENERAL NATURE OF FATS. 
The appearance and physical properties of the common fats and 
oils used for food purposes are too well known to require much de- 
scription here. Chemically considered, fats consist chiefly of glyc- 
erids of fatty acids. The fatty acids whose glycerids are most com- 
mon in edible fats are oleic, linolic, palmitic, and stearic. One fat 
differs from another primarily in the proportions of these esters 
which it contains and in the presence or absence of small quantities 
of other substances, such as free fatty acids and characteristic flavor- 
ing and coloring bodies. 
The melting point or hardness of any fat depends on the relative 
proportions of these acids present, and fats containing large amounts 
of combined oleic and linolic acids are soft or liquid, while those con- 
taining large amounts of palmitic or stearic acid are solid. This 
follows whether the respective acids are combined as triglycerids or 
as mixed glycerids. 
The color of some of the crude fats and oils varies from light yel- 
low to red, or even black, but the refining processes remove a great 
proportion of the color-giving bodies, and the pure fats and oils are 
a pale yellow or colorless when liquid, and white or creamy white 
when solid. 
The flavors and odors of fats are probably due to the presence in 
them of small amounts of difficultly removable substances rather 
than to specific properties of the pure fats themselves, in view of 
the fact that flavors and odors become much less noticeable the more 
completely the fats are purified. The characteristic flavor of butter, 
for example, is due to the absorption by the fat of the substances 
