2 BULLETIN 469, U. S. DEPARTMENT OP 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 



