PRODUCTION AND UTILIZATION OF FATS AND OILS 27 
ANIMAL FATS AND OILS 
The composition of any animal fat or oil is influenced by the 
inherent variations of animal fats and also by the food eaten by 
the animal, so that they vary more widely in composition than do 
the vegetable oils. Like the nondrying vegetable oils, most land- 
animal fats do not easily absorb oxygen, but, like the drying vege- 
table oils, most marine-animal oils readily absorb oxygen. 
MILK FAT 
Milk fat is the most universally and extensively produced fat. 
In the United States the yearly production of this fat, in the form 
of butter, cheese, ice cream, and butter substitutes, amounts to about 
3,000,000,000 pounds. 
Butter is an emulsion of milk fat and water containing small 
quantities of casein, milk sugar, and inorganic salts. The legal 
requirement is that it shall contain at least 80 per cent of milk fat. 
The butter substitutes now on the American market are of two 
classes — true oleomargarine, which contains oleo oil and neutral lard, 
and vegetable or nut margarines, which contain no animal fats other 
than that in the ripened milk used. Margarines of both types show 
a wide variation in composition. Not only are the formulas the 
secret of each manufacturer, but the ingredients in a given brand 
may vary with the season and with the fluctuations in the market 
price of the fats and oils used. All are made according to the same 
general procedure. 
LARD 
In making kettle-rendered lard the leaf fat is pulled from the 
warm carcasses of hogs and immediately chilled. When thoroughly 
cooled, the fat is hashed and heated in steam- jacketed kettles until 
the oil separates from the tissues. It is then salted and allowed to 
stand in a melted condition until the fine particles of membrane 
settle. After the lard has been freed from all particles, it is packed 
in shipping packages and placed in cold storage. The cracklings, or 
residue left after rendering, are either pressed to obtain the residual 
lard or placed in the steam lard tanks. This rendering of lard in 
steam- jacketed kettles is merely a modification adapted to plant 
production of the old home procedure of making lard by cooking 
the hog fat in a large pan or kettle over an open fire or on a stove. 
Neutral lard, or neutral, as the packers call it, is made by cooking 
the first grade of leaf fat in much the same manner as the kettle- 
rendered lard, but at a lower temperature (126° to 128° F.), so that 
it retains practically no hog flavor. It is used in the manufacture 
of oleomargarine. 
Steam lard is rendered by live steam. The chopped fat is charged 
into steel tanks. After the covers have been fastened clown, live 
steam is admitted through the bottoms of the tanks until the lard 
has separated from the tissues or fat membranes. The water and 
solids are then allowed to settle, after which the lard is drawn off 
from the water and solid residue. As some darkening of the lard 
occurs during the cooking and its flavor is frequently strong, it is 
customary to bleach and deodorize it in a manner similar to the 
treatment of cottonseed oil (p. 7). 
