Oil Information Center

Oils (Fr. buile) are a type of fat that remains liquid at room temperature. Cooking oils are refined from various seeds, plants and vegetables. When purchasing oils, you should consider their use, smoke point, flavor and cost. Fats, including oils and shortenings, are manufactured for specific purposes such as deep-frying, cake-baking, salad dressings and sautéing. Most food service operations purchase different ones for each of these needs.

Fats break down at different temperatures. The temperature at which a given fat begins to break down and smoke is known as its smoke point. Choose fats with higher smoke points for high temperature cooking such as deep-frying and sautéing. If a fat with a low smoke point is used for high temperature cooking, it may break down, burn and impart undesirable flavors.

The flavor and cost of each oil must also he considered. For example, both corn oil and walnut oil may be used in a salad dressing. Their selection may depend on balancing cost (corn oil is less expensive) against flavor (walnut oil has a stronger, more distinctive flavor).

When fats spoil, they are said to go rancid. Rancidity is a chemical change caused by exposure to air, light or heat. It results in objectionable flavors and odors. Different fats turn rancid at different rates, but all fats benefit from refrigerated storage away from moisture, light and air. (Some oils are packaged in colored glass containers because certain tints of green and yellow block the damaging light rays that can cause an oil to go rancid.)

Although oils may become thick and cloudy under refrigeration, this is not a cause for concern. The oils will return to their clear, liquid states at room temperature. Stored fats should also be covered to prevent the absorption of odors. Vegetable oils are extracted from a variety of plants, including corn, cottonseed, peanuts and soybeans, by pressure or chemical solvents. The oil is then refined and cleaned to remove unwanted colors, odors or flavors. Vegetable oils are virtually odorless and have a neutral flavor. Because they contain no animal products, they are cholesterol-free.

If a commercial product contains only one type of oil, it is labeled "pure" as in pure corn oil". Products labeled "vegetable oil" are blended from several sources. Products labeled 'salad oil' are highly refined blends of vegetable oil. Canola oil is processed from rapeseeds. Its popularity is growing rapidly because it contains no cholesterol and has a high percentage of monounsaturated fat. Canola oil is useful for frying and general cooking because it has no flavor and a high smoke point.

Nut oils
Nut oils are extracted from a variety of nuts and are almost always packaged as a "pure" product, never blended. A nut oil should have the strong flavor and aroma of the nut from which it was processed. Popular examples are walnut and hazelnut oils. These oils are used to give flavor to salad dressings, marinades and other dishes. But heat diminishes their flavor, so nut oils are not recommended for frying or baking. Nut oils tend to go rancid quickly and therefore are usually packaged in small containers.

Olive oil
(Fr. buile diolive) Olive oil is the only oil that is extracted from a fruit rather than a seed, nut or grain. Olive oil is produced primarily in Spain, Italy, France, Greece and North Africa; California produces a relatively minor amount of olive oil. Like wine, olive oils vary in color and flavor according to the variety of tree, the ripeness of the olives, the type of soil, the climate and the producer's preferences.

Colors range from dark green to almost clear, depending on the ripeness of the olives at the time of pressing and the amount of subsequent refining. Color is not a good indication of flavor, however. Flavor is ultimately a matter of personal preference. A stronger-flavored oil may be desired for some purposes, a milder oil is better for others. Good olive oil should be thicker than refined vegetable oils, but not so thick that it has a fatty texture.

The label designations (extra virgin, virgin and pure) refer to the acidity of the oil (a low acid content is preferable) and the extent of processing used to extract the oil. The first cold-pressing of the olives results in virgin oil. (The designation "virgin" is used only when the oil is 100% unadulterated olive oil, unheated and without any chemical processing.) Virgin oil may still vary in quality depending on its acidity level.

Extra virgin oil is virgin oil with an acidity level of not more than 1%; virgin oil may have an acidity level of up to 3%. Pure olive oil is processed from the pulp left after the first pressing using heat and chemicals. Pure oil is lighter in flavor and less expensive than virgin oil.

Flavored oils
They are also known as infused oils, are an interesting and increasingly popular condiment. These oils may be used as a cooking medium or flavoring accent in marinades, dressings, sauces or other dishes. Flavors include basil and other herbs, garlic, citrus and spice.

Flavored oils are generally prepared with olive oil for additional flavor or canola oil, both considered more healthful than other fats. Top-quality commercially flavored oils are prepared by extracting aromatic oils from the flavoring ingredients and then emulsifying them with high-grade oil; any impurities are then removed by placing the oil in a centrifuge. Using the aromatic oils of the flavoring ingredients yields a more intense flavor than merely steeping the same ingredients in the oil. Flavored oils should be stored as you would any other high-quality oil.