Fats And Oils

Knowledge of fats and oil is necessary as well as knowing how to use them in food preparation and cooking.

Fats and oils are composed of the elements carbon, hydrogen, and oxygen in the form of glycerides or compounds of fatty acids and glycerol. The properties of fats will differ according to the properties of the fatty acids of which they are composed. The ratio of carbon and hydrogen to oxygen in the fat molecule, however, is much greater than that in a carbohydrate. As an example, a fat found in beef that is tristearin has 110 atoms of hydrogen to 6 atoms of oxygen, as compared to the two-to-one ratio of the same elements in the carbohydrate glucose. The chemical term for a fat is triglyceride. All foot fats are mixtures of glycerides and variation in mixtures accounts for the wide variation in consistency, flavor, and chemical properties of various food fats.

Fats and oils play an important role in human nutrition because they are sources of energy and of the essential fatty acids in the diet. In addition, fat deposits in the body serve as insulation and provide protective cushions for the organs. Fats are the most concentrated form of energy in foods, yielding more than twice as much energy as equal portions of either carbohydrates or proteins. There are certain fatty acids which man needs for good health that the body cannot product. These are the essential fatty acids, and include the following three acids: linoleic, linolenic, and arachidonic. Fats are known to protect the body in two ways. The deposits of fat under the skin act as nonconductors of heat, helping to insulate the body and prevent the rapid loss of heat. Furthermore, the viscera and certain organs of the body, such as the kidneys, are supported and cushioned by fat.

In the pure form one pound of fat yields about 4,000 calories that is more than two times the calories furnished by an equal quantity of protein or carbohydrate. Fats are also valuable for the flavor, richness, and satiety quality that they give to meals. Some fats and oils contain fatty acids essential for good nutrition and some fats are sources of the fat soluble vitamins A, D, and E. Refined vegetable oils and hydrogenated fat contain little or no vitamin A although in their natural state some yellow-colored vegetable oils may contain appreciable amounts.

The richest sources of fat in the diet are the vegetable oils, such as corn oil, peanut oil, olive oil, and vegetable shortenings, and the animal fats, such as lard and butter. Nuts rank high as contributors of fat to the diet. Meat, poultry, and fish vary in their fat content; bacon contains about twice as much as beef and salmon (an example of fatty fish). All cheeses except for cottage cheese contain appreciable amounts of the nutrient. The fat in an egg is found only in the yolk. Most fruits and vegetables contain little fat; however, avocados and coconuts, which contain about 20 per cent fat, are exceptions.

The form of a glyceride, whether it is liquid or solid, depends on the kind of fatty acids in its structure. A glyceride that is liquid at room temperature is called an oil and contains more of the unsaturated fatty acids. A glyceride that is solid at room temperature contains more of the saturated fatty acids in its structure is called a fat. Oils are the predominant glycerides in plants; fats are the predominant gylcerides in animals. Oils have a predominance of olein that is liquid at ordinary temperatures. The presence of small quantities of solid fats in oils is shown when oils are subjected to cold temperatures. The higher melting fats solidify, giving the oil a cloudy appearance. Some oils have had the solid fats filtered out in the manufacturing process. This treatment is called "wintering" or "winterizing."

Essential oils are oily substances manufactured by some plants. Their aromatic properties are responsible for the fragrance and flavor that they impart. Oils of lemon, orange, cinnamon and cloves are some of the volatile oils used as such for flavor or combined with alcohol in the manufacture of extracts.

Butter is the fat of cream separated almost completely from the other milk constituents by agitation or churning. Butter is made from either sweet or sour cream. The cream may be allowed to sour naturally or may be acidified by the addition of a pure culture of lactic-acid bacteria to pasteurized cream. Some sweet-cream butter is marketed unsalted as "sweet "butter but salted butter is preferred by most persons. Coloring matter is added to the cream before churning. The characteristic flavor of butterfat is now thought to be due largely to the presence of acetylmethylcarbinol and diacetyl, which is a bacterial oxidation product of acetylmethylcarbinol. Off-flavors in butter are thought to be due largely to oxidation.

Margarine is a plastic food made from one of more optional fat ingredients churned with cultured pasteurized skim milk. The lower cost of margarine within recent years has resulted from better information concerning its composition and sanitary quality, its fortification with vitamin A, ad the improved care and refrigeration being applied by the retailer. Better methods of refining and stabilizing the oils used, especially soyoil, and the developments of better physical properties such as flavor and texture have resulted in an excellent product.

Lard is the fat separated from fat tissues of the hog. The quality of lard depends upon such factors as the part of the body from which the fat is obtained, from the feed used for fattening the animal, and the rendering process. Leaf fat that lines the abdominal cavity is the best fat of the animal and has been used for making the better qualities of lard. Some producers of lard are combining lard with hydrogenated vegetable oils and with emulsifiers and antioxidants. Such fats, being a combination of lard and vegetable oils cannot be labeled lard but be given a trade name. In the list of ingredients the term "meat fat" is sometimes used instead of lard.

The addition of hydrogen to unsaturated fats, thus converting oils into solid fats, is known as hydrogenation. The fats so produced are neutral in flavor, have a high enough smoking temperature to make them useful for frying, and have good shortening power. Some hydrogenated fats have been undesirably hard when refrigerated, because they were too highly hydrogenated. Today, because of the market demand for unsaturated fat products, a processing method is used in which all the oil or fat undergoes partial hydrogenation. This process increases the firmness of the glyceride without producing saturated fatty acids (selective hydrogenation). In selective hydrogenation the polyunsaturated fatty acids are changed to monounsaturated rather than saturated fatty acids.

The principal oils on the market are those from cottonseed, corn, soybeans, peanuts, and olives. All oils are refined except for the better grades of olive oil. All salad and cooking oils must be accurately labeled to enable the purchaser to know whether the oil is from a single source (olive, peanut, corn) or is a mixture of oils.

Most fats and oils need protection from air, heat and light. Fats and oils in partially filled containers keep longer if they are transferred to smaller containers in which there is little or no air space. Some butter, fat drippings and margarine tightly wrapped or covered, in the refrigerator. These products are best used within two weeks. Do not let butter or margarine stand for long periods at room temperature as exposure to heat and light hastens rancidity. Keep small quantities of cooking and salad oils at room temperatures and use before flavor changes. For long storage, keep oils in the refrigerator even though some my cloud and solidify in the refrigerator. This is not harmful. If warmed to room temperature, they will become clear and liquid. Hydrogenated shortenings and lard have been stabilized by hydrogenation or antioxidants. They can be held at room temperature. Lard that is not stabilized should be refrigerated. Keep mayonnaise and other salad dressings including home made dressing in the refrigerator. These products should be refrigerated after opening.

Besides changes described above which occur in fats under ordinary storage conditions, certain other changes occur when fats are heated to high temperatures. One evidence of the decomposition of fats by heating is visible fumes. In the use of fats for frying it is important to avoid the smoke point. By using a thermometer and regulating the source of heat one can prevent decomposition. Todays domestic oils such as soybean, cottonseed, peanut and corn if well refined and deodorized have smoking points of about 232 degree C or 450 degree F. Some peanut and corn oil products are apt to be less well processed and may smoke at 221 to 226 degree C or 450 to 440 degree F. Hydrogenated shortenings (without emulsifier) sometimes contain minor amounts of palm and coconut oils and may be found to smoke anywhere with the range of 221 to 232 degree C or 430 to 450 degree f. Frying can be accomplished in two ways: (1) pan-frying in which shallow fat is used and (2) deep-fat frying in which the food is submerged in fat. After frying, foods require draining on absorbent paper to remove excess fat. It is desirable to fold fat absorption to a minimum during frying.

It can be confusing when one is in the grocery store as there are so many different fats and oils. It is wise to keep in mind the use for which a certain product is bought. They will vary according to the needs of the household. Butter, because of its flavor, is often preferred for table use, some baked products, and the seasoning of some foods. Margarine will serve the same purchase at much less cost. Oil can be bought for salad dressings and for frying. Shortening or lard is bought for both shortening and frying.

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