OIL

OIL. Oil is liquid fat, usually plant-derived, used as a cooking medium, as a lubricant to keep food from sticking to pans, and as a source of flavor. Oil from animal sources, particularly fish oil, is also used as a nutritional supplement. Oil is also ubiquitous in processed foods.

The difference between oil and fat is that oil is liquid at room temperature while fat is solid. Chemically, both are composed of hydrocarbon chains and are potent sources of energy. The strong molecular bonds of fats and oils make them relatively resistant to heat and thus suitable for high-heat cooking methods such as deep-frying. Oil can be used in conjunction with other fats, such as butter, to raise the temperature of the other fat at which it would otherwise begin to break down and smoke.

History of Oil

Olive oil and sesame oils are among the most ancient oils in the Western world, dating back to 4,000 years or more. Olive trees are relatively simple to cultivate and, once the olives are prepared, the oil can be obtained by pressing. Both olive oil and sesame oil were used in southern Europe, while northern countries typically used animal fats such as lard or goose fat.

In the Orient, oil was pressed from soybeans, while sesame, mustard seed, and safflower oils were used in India and ancient Egypt. Peanuts, corn, and sunflower seeds were available in the New World, but oil was generally extracted only from squash seeds, especially squash belonging to the species Cucurbita pepo.

The nineteenth century saw the rise of international trade in tropical oils, particularly palm and coconut oil. The raw materials, which included hearts of palm and dried coconut meat (copra), were exported from Africa and the Pacific islands to industrial countries to be pressed for oil. The vast production of corn in the United States provided a source of oil to be used in cooking and in the manufacture of oleomargarine.

In nineteenth-century Africa, both the French and British introduced larger-scale peanut farming specifically for peanut oil, which was used as an adulterant in cheap grades of olive oil, and as a base ingredient in soap.

Composition of Oils

Oils, like other fats, consist mostly of triglycerides, which are three fatty acids attached to a molecule of glycerol (an alcohol built around three atoms of carbon). A fatty acid consists of a carboxyl group (carbon, oxygen, and hydrogen linked together), which in turn is linked to a hydrocarbon chain. The more the hydrocarbon chain is filled with hydrogen atoms, the more chemically stable it will be. A fatty acid fully loaded with hydrogen is said to be "saturated," while a less hydrogen-rich acid is "monounsaturated" or "polyunsaturated," depending on its structure. Oleic acid is a common monounsaturated fat, while linoleic acid is the most common polyunsaturated fatty acid.

The more saturated a fat is, the more likely it is to be solid at room temperature (such as lard or shortening). Oils are liquid because they are less saturated than fats. They are also less shelf-stable because their chemical structures are more likely to be affected by exposure to oxygen, causing them to become rancid or develop offflavors. To make the product more stable, food processors pump hydrogen through the oil to fill in the gaps in its chemical structure, a process known as "hydrogenation." Highly hydrogenated oil is creamy or solid at room temperature, useful for making oleomargarine or other processed food products.

Oils generally have about the same caloric value of approximately 120 calories per tablespoon whether the fatty acids are saturated or not. More important to health-conscious consumers is the role of fatty acids in raising or lowering the presence in the bloodstream of the high-density lipoprotein (HDL) or low-density lipoprotein (LDL) associated with cholesterol. HDL (the "good cholesterol") is a beneficial substance that helps the body get rid of excess cholesterol, while LDL (the "bad cholesterol") builds up in the arteries and can increase the risk of heart disease. Eating foods high in monounsaturated fatty acids is believed to help lower LDL cholesterol levels and decrease the risk of heart disease, while the consumption of saturated fats may increase levels of LDL and total cholesterol. The consumption of polyunsaturated fats in place of saturated fats decreases LDL cholesterol levels. The American Heart Association recommends the consumption of oils that have no more than two grams of saturated fat per tablespoon.

Unsaturated fat content is a major selling point for household oils. One of the major oils on the market, canola oil, was developed specifically to appeal to consumers concerned about fat content. Canola—short for "Canadian oil"—is a variety of the rapeseed plant developed in Canada with less fatty acid than the traditional variety and thus a lower level of saturated fat than most other oils.

The chemical structure of oils makes them relatively stable at high temperatures, but at some point oil begins to break down and give off smoke; beyond this point there is danger of fire. The smoke point for most oils is around 410°F (210°C), although some oils have even higher smoke points. The smoke point gets lower as oil is reused due to degradation of chemical bonds and contamination of the oil with food particles. Commercial operations that re-use oil will pass it through a filter to take out the contaminants.

Sources of Oil

In addition to olives, oil is obtained from legumes such as peanuts and soybeans; from the seeds of many plants, including corn, rapeseed (canola), sesame, cottonseed, sunflower, palm, safflower, coconut, grapeseed, mustard, pumpkin, and avocado; and from tree nuts such as walnuts,

almonds, hazelnuts, and pistachios. Tree nut oils are usually expensive and do not respond well to high heat, so they are used primarily to dress salads or to add flavor to baked goods.

The finest oils are simply extracted from the raw material (such as olives or nuts) by pressure. This is called "cold pressed" or "first pressed" oil. Oil that remains bound up in the raw material can be extracted by heat or chemical solvents.

Oils labeled by specific names, such as peanut oil, are obtained from those particular plants; a product labeled merely "vegetable oil" is a blend of various oils. In the production of vegetable oils, seeds are cracked, cooked, and run through a press to extract readily obtainable oil. The pulp is further processed to obtain the rest of the oil, which is neutral and tasteless; if flavor is desired, the oil can be mixed with the product of the first pressing to restore flavor and color.

Uses of Oil

Oil has a variety of uses in cooking, most of them based on its ability to transfer heat to the food while remaining stable itself. Asian food is often stir-fried in a little hot oil, just enough to keep the food from sticking to the pan. Chicken can be sautéed or fricasseed in a few tablespoons of oil, while pieces of breaded fish can be fried in shallow oil—perhaps a quarter of an inch deep.

Frying large pieces of food in deep oil requires a temperature of 350° to 375°F (177° to 191°C). At that temperature, the hot oil will sear the surface of the food being fried, trapping moisture within the food. The food thus cooks in its own moisture rather than in the oil, which is why properly fried food is not greasy. Greasiness results from frying at a temperature lower than optimal.

In Italy, olive oil is used as a dipping sauce for bread at the table. Olive oil is preferred as a salad dressing because it has its own flavor to contribute to the dish.

In food manufacturing, oils are used in a host of products, ranging from soups and gravies, salad dressings, bread and rolls, and fried foods to nondairy toppings and frozen desserts, coffee creamers and cocoa mixes, candy bars and cakes, and in most processed snack foods.

Fish Oil

Some species of fish such as Atlantic menhaden have high levels of certain essential fatty acids, called omega-3 fatty acids, which the human body is not able to synthesize by itself and must obtain from food. Oil made from these fish is sold as a nutritional supplement. Menhaden oil is used in the production of margarine and shortening in Europe and has been approved for use in the United States.

See also Butter; Cooking; Fats; Fish; Frying; Snacks .

BIBLIOGRAPHY

Lane, Mark, and Judy Ridgway. The Simon and Schuster Pocket Guide to Oil, Vinegars, and Seasonings. New York: Simon and Schuster, 1990.

McGee, Harold. On Food and Cooking: The Science and Lore of the Kitchen. New York: Fireside Books, 1984.

Pehaut, Yves. "The Invasion of Foreign Foods." In Food: A Culinary History from Antiquity to Present, edited by Jean-Loius Flandrin and Massimo Montanari, pp. 457–463. New York: Penguin Books, 1999.

Tannahill, Reay. Food in History. New York: Three Rivers Press, 1988.

Richard L. Lobb

oils term commonly used to indicate a variety of greasy, fluid substances that are, in general, viscous liquids at ordinary temperatures, less dense than water, insoluble in water but soluble in alcohol and ether, and flammable. These substances, however, differ so much among themselves in chemical composition that, in chemistry, their classification in one group is not practical and is employed only in a general way in accordance with popular usage. Petroleum and substances obtained from it, which are mixtures of hydrocarbons , are classed together, because of their origin, as mineral oils. They are widely used as fuels, illuminants, and lubricants. Distinguished from these in that they are obtained from animals and plants and are mixtures of carbon-hydrogen-oxygen compounds are the fatty oils or fixed oils. There is fundamentally no difference between fatty oils and fats (see fats and oils ). Such oils are used extensively as lubricants and in the making of soap . Depending upon their ability to oxidize when exposed to the atmosphere and form a thin, skinlike layer over substances upon which they are spread, the fixed, or fatty, oils are classed as drying or nondrying oils. The drying oils, e.g., linseed, hempseed, and poppy seed oil, are used in making paints and varnishes. On the other hand, such vegetable oils as olive, rapeseed, and castor oil and such animal oils as lard oil and neat's-foot oil do not possess this property and fall into the nondrying group. Another large and varied group of oils is recognized, the essential oils or volatile oils, which occur in plants but differ from the fixed, or fatty, oils in that they are volatile. In general, they give to the plant in which they are found its characteristic odor, flavor, or other properties peculiar to it.

oil / oil/ • n. 1. a viscous liquid derived from petroleum, esp. for use as a fuel or lubricant. ∎  petroleum. ∎  any of various thick, viscous, typically flammable liquids that are insoluble in water but soluble in organic solvents and are obtained from animals or plants: potatoes fried in vegetable oil. ∎  a liquid preparation used on the hair or skin as a cosmetic: suntan oil. ∎ Chem. any of a group of natural esters of glycerol and various fatty acids that are liquid at room temperature. Compare with fat. 2. (often oils) oil paint: a portrait in oils. • v. [tr.] [often as adj.] (oiled) lubricate or coat (something) with oil: a lightly oiled baking tray. ∎  impregnate or treat (something) with oil: her hair was heavily oiled. PHRASES: oil and water fig. used to refer to two elements, factors, or people that do not agree or blend together.DERIVATIVES: oil·less adj. ORIGIN: Middle English: from Old Northern French olie, Old French oile, from Latin oleum ‘(olive) oil’; compare with olea ‘olive.’

oil General term to describe a variety of substances whose chief shared properties are viscosity at ordinary temperatures, a density less than that of water, inflammability, insolubility in water, and solubility in ether and alcohol. Mineral oils, most notably crude oil or petroleum oil, are used as fuels. Animal and vegetable oils (fatty oils or fats) are used as food, lubricants and as a major ingredient of soap. In addition, there are essential oils from plants that, unlike fatty oils, are volatile. Fatty oils can be classified into two groups: drying, such as linseed and poppyseed oil, and non-drying, such as olive and castor oil.

oil in early use, liquid expressed from the olive; later, any similar viscid smooth liquid. XII. ME. oli(e), oile — AN., ONF. olie, OF. oile (mod. huile) — L. oleum (olive) oil, for *oleiuom, *olaiwom — Gr. élai(F)on; cf. OLIVE. The adoption from F. ousted OE., ME. ele = OS., OHG. oli (Du. olie, G. öl) — popL. olium, L. oleum.
Hence oily (-Y1) XVI.

oil used in several phrases relating to oil as a smooth and viscous liquid.
oil and water taken as a type of two elements, factors, or people that do not agree or blend together.
oil someone's palm bribe a person.
oil the wheels help something go smoothly.

See also burn the midnight oil, pour oil on troubled waters.

oil n.
1. a viscous liquid derived from petroleum, especially for use as a fuel or lubricant.

2. petroleum.
v.
1. lubricate or coat (something) with oil.

2. supply with oil as fuel: do not oil individual tanks too rapidly.
oilless adj.

oil Any of various viscous liquids that are generally immiscible with water. Natural plant and animal oils are either volatile mixtures of terpenes and simple esters (e.g. essential oils) or are glycerides of fatty acids.

oil Olive oil was important in Israelite economy (Num. 18: 12), used for light (Exod. 27: 20), cooking (Ezek. 16: 13), and healing (Mark 6: 13), and as hair conditioner (Ps. 23: 5). See anointing.

oil. See petroleum industry.

oil See PETROLEUM.

oil •boil, Boyle, broil, coil, Dáil, Doyle, embroil, Fianna Fáil, foil, Hoyle, moil, noil, oil, roil, Royle, soil, spoil, toil, voile •parboil • trefoil • jetfoil • airfoil •cinquefoil • milfoil • tinfoil • multifoil • aerofoil • hydrofoil •counterfoil • gargoyle • turmoil •charbroil • topsoil • subsoil