Surface exposed. They report that the smoking temperature for a
particular fat is lowered when the surface exposed is increased. Thus the
wider the diameter of the cooking utensil used, the more the smoking
temperature is lowered. They advise using a vessel with as small a diameter
as is convenient for deep fat frying.
Foreign particles. They have found that another factor that lowers
the smoking temperature is the presence of finely divided foreign particles
in the fat. Flour and small particles of other materials accumulate in a
fat used for cooking purposes. Hence, a much-used fat has a lower smoking
temperature than the original fat.
Smoking temperature and fat absorption. The cooperators in fat
investigations at Iowa State College found that absorption of fat by dough-
nuts is influenced to a greater degree by the smoking point of the fat than
by any other chemical or physical factors investigated. Fat absorption was
greater the lower the smoking point of the fat or oil.
Rancidity
Fats are added directly to many products such as crackers, cookies, and
cake because of their shortening power; they are added to other products
in the form of such ingredients as nut meats, coconut, fatty seeds, milk,
and cheese. Prevention of rancidity may become a problem in such baked
goods as crackers, cookies, and fruit cake which may be stored for longer
or shorter periods; in the cereal industry; in the confectionery industry;
in dairy products; in the fat and oil industry; in salad dressings; and in
storage of meats, particularly cured meats such as bacon and ham, and in
stored frozen fresh meats. Meat, the fat of which contains more unsaturated
glycerides, is subject to the development of rancidity more rapidly than fat
containing greater percentages of saturated glycerides. Thus frozen poultry
and pork present more problems when stored for long periods than beef
and mutton.
Types of fat spoilage. The chemical change that needs to occur in a
fat before taint is detectable organoleptically is very small. Davies states
that butyric and capric acids are detectable by smell and taste in concentra-
tions of less than 80 parts per million parts of fat. Changes in fats can be
550 FATS AND OILS
detected by smell and taste before they can be detected by chemical tests.
An isolated fat possessing excellent keeping qualities may show deteriora-
tion rapidly after it is combined with other ingredients, and vice versa ;
but, in general, the fresher the fat and the better its keeping quality, the
better the keeping quality of the product with which it is combined.
Different types of spoilage may occur in fats. Davies says "mustiness"
is due to microorganic breakdown of higher fatty acids and is accelerated
by moisture. Mustiness is common in cereal products, particularly maize.
Davies states it is accompanied by an increase in acidity of water extracts,
matting of the product because of mold growth, and local spontaneous
heating. It is prevented by keeping the humidity sufficiently low.
"Fishiness," according to Davies, is due to the production of trimethyl-
amine in the presence of catalysts from lecithin, before the auto-oxidation
of the fat proper. Fishiness occurs most commonly in butter. The presence
or absence of other products can alter the fishy odor.
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Surface exposed. They report that the smoking temperature for a
particular fat is lowered when the surface exposed is increased. Thus the
wider the diameter of the cooking utensil used, the more the smoking
temperature is lowered. They advise using a vessel with as small a diameter
as is convenient for deep fat frying.
Foreign particles. They have found that another factor that lowers
the smoking temperature is the presence of finely divided foreign particles
in the fat. Flour and small particles of other materials accumulate in a
fat used for cooking purposes. Hence, a much-used fat has a lower smoking
temperature than the original fat.
Smoking temperature and fat absorption. The cooperators in fat
investigations at Iowa State College found that absorption of fat by dough-
nuts is influenced to a greater degree by the smoking point of the fat than
by any other chemical or physical factors investigated. Fat absorption was
greater the lower the smoking point of the fat or oil.
Rancidity
Fats are added directly to many products such as crackers, cookies, and
cake because of their shortening power; they are added to other products
in the form of such ingredients as nut meats, coconut, fatty seeds, milk,
and cheese. Prevention of rancidity may become a problem in such baked
goods as crackers, cookies, and fruit cake which may be stored for longer
or shorter periods; in the cereal industry; in the confectionery industry;
in dairy products; in the fat and oil industry; in salad dressings; and in
storage of meats, particularly cured meats such as bacon and ham, and in
stored frozen fresh meats. Meat, the fat of which contains more unsaturated
glycerides, is subject to the development of rancidity more rapidly than fat
containing greater percentages of saturated glycerides. Thus frozen poultry
and pork present more problems when stored for long periods than beef
and mutton.
Types of fat spoilage. The chemical change that needs to occur in a
fat before taint is detectable organoleptically is very small. Davies states
that butyric and capric acids are detectable by smell and taste in concentra-
tions of less than 80 parts per million parts of fat. Changes in fats can be
550 FATS AND OILS
detected by smell and taste before they can be detected by chemical tests.
An isolated fat possessing excellent keeping qualities may show deteriora-
tion rapidly after it is combined with other ingredients, and vice versa ;
but, in general, the fresher the fat and the better its keeping quality, the
better the keeping quality of the product with which it is combined.
Different types of spoilage may occur in fats. Davies says "mustiness"
is due to microorganic breakdown of higher fatty acids and is accelerated
by moisture. Mustiness is common in cereal products, particularly maize.
Davies states it is accompanied by an increase in acidity of water extracts,
matting of the product because of mold growth, and local spontaneous
heating. It is prevented by keeping the humidity sufficiently low.
"Fishiness," according to Davies, is due to the production of trimethyl-
amine in the presence of catalysts from lecithin, before the auto-oxidation
of the fat proper. Fishiness occurs most commonly in butter. The presence
or absence of other products can alter the fishy odor.