1.4: Oils

Oils are a type of fat that remains liquid at room temperature. Cooking oils are refined from various seeds, plants and vegetables. When purchasing oils, 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 clown at different temperatures. When fats break down, their chemical structure is altered - the triglyceride molecules that make up fat are converted into individual fatty acids. These acids add undesirable flavors to the fat and can ruin the flavor of the food being cooked. The temperature at which a given fat begins to break down an d smoke is known as its smoke point. Select fats with higher smoke points for high-temperature cooking such as deep-frying and sautéing.

The flavor and cost of each oil must be considerations. For example, both corn oil and walnut oil can 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).

Terms:

• smoke point the temperature at which a fat begins to break down and smoke.
• flash point the temperature at which a fat ignites and small flames appear on the surface of the fat.
• shortening (1) a white , flavorless, solid fat formulated for baking or deepfrying; (2) any fat used in baking to tenderize the product by shortening gluten strands.

When fats spoil, they go rancid. Rancidity is a chemical change cause d 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 container s 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 them from absorbing odors.

Vegetable oils are extracted from a variety of plants, including corn, cottonseed, peanuts, grape seeds, sesame seeds 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 are extracted from a variety of nuts and are usually 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. 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 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 foods, while 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 the level of free acidity, expressed as oleic acid. Extra virgin oil is virgin oil with not more than 1% free acidity (oleic acid); virgin oil may have 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, also known as infused oils, are an interesting and increasingly popular condiment. These oils may be used as a dip for breads, a cooking medium or a 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 a 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.