Cooking oil is purified fat of plant origin, which is usually liquid at room temperature (Saturated oils such as coconut and palm are more solid at room tempurature than other oils).
Some of the many different kinds of edible vegetable oils include: olive oil, palm oil, soybean oil, canola oil, pumpkin seed oil, corn oil, sunflower oil, safflower oil, peanut oil, grape seed oil, sesame oil, argan oil and rice bran oil. Many other kinds of vegetable oils are also used for cooking.
The generic term "vegetable oil" when used to label a cooking oil product refers to a blend of a variety of oils often based on palm, corn, soybean or sunflower oils.
Oil can be flavored by immersing aromatic food stuffs such as fresh herbs, peppers, garlic and so forth in the oil for a period of time. However, care must be taken when storing flavored oils to prevent the growth of Clostridium botulinum (the bacteria that produces toxins that can lead to botulism).
Health and nutrition
The appropriate amount of fat as a component of daily food consumption is the topic of some controversy. Some fat is required in the diet, and fat (in the form of oil) is also essential in many types of cooking. The FDA recommends that 30% or less of calories consumed daily should be from fat. Other nutritionists recommend that no more than 10% of a person's daily calories come from fat. In extremely cold environments, a diet that is up to two-thirds fat is acceptable and can, in fact, be critical to survival.
While consumption of small amounts of saturated fats is essential, meta-studies conducted by several scientists find high corelation between excessive amounts of such fats and coronary heart disease. Mayo Clinic highlighted oils that are high in saturated fats include coconut, palm oil and palm kernel oil. Those of lower amounts of saturated fats, and higher levels of unsaturated (preferably monounsaturated) fats like olive oil, peanut oil, canola oil, avocados, safflower, corn, sunflower, soy, musterd and cottonseed oils are generally healthier. The National Heart, Lung and Blood Institute and World Heart Federation have urged saturated fats be replaced with polyunsaturated and monounsaturated fats. The health body lists olive and canola oils as sources of monosaturated oils while soybean and sunflower oils are rich with polyunsaturated fat. A 2005 research in Costa Rica suggests consumption of non-hydrogenated unsaturated oils like soybean and sunflower over palm oil.
The labelling of the cholesterol content of foods on the basis of their total saturated fats content is unjustified because not all saturated fats are equally cholesterolemic. Palmitic acid in palm oil, does not behave like other saturated fats, and is neutral on cholesterol levels because it is equally distributed among the three “arms” of the triglyceride molecule. Studies have indicated that palm oil consumption reduces blood cholesterol in comparison with other traditional sources of saturated fats such as coconut oil, dairy and animal fats.
In 2007, scientists Kenneth C. Hayes and Pramod Khosla of Brandeis University and Wayne State University indicated research focus has shifted from saturated fats to individual and total composite of fatty acids (saturates, monounsaturates, polyunsaturates) that comprise our daily fat intake. An adequate intake of both polyunsaturated and saturated fats is needed for the ideal LDL/HDL ratio in blood, as both contribute to the regulatory balance in lipoprotein metabolism.
Olive oil's high oleic fatty acids raises "good" HDL cholesterol, a heart-healthy effect that need not be limited by an arbitrary figure.
Peanut, cashew and other nut-based oils may also present a hazard to persons with a nut allergy. A severe allergic reaction may cause anaphylactic shock and result in death.
Trans fats
Unlike other dietary fats, trans fats are not essential, and they do not promote good health. The consumption of trans fats increases one's risk of coronary heart disease by raising levels of "bad" LDL cholesterol and lowering levels of "good" HDL cholesterol. Trans fats from partially hydrogenated oils are more harmful than naturally occurring oils.
Several large studies indicate a link between consumption of high amounts of trans fat and coronary heart disease, and possibly some other diseases. The United States Food and Drug Administration (FDA), the National Heart, Lung and Blood Institute and the American Heart Association (AHA) all have recommended people to limit intake of trans-fat.
Cooking with oils
Heating an oil changes its characteristics. Oils that are healthy at room temperature can become unhealthy when heated above certain temperatures. When choosing a cooking oil, it is important to match the oil's heat tolerance with the cooking method.
A 2001 parallel review of 20-year dietary fat studies in the United Kingdom, the United States of America and Spain concluded that polyunsaturated oils like soya, canola, sunflower and corn degrade easily to toxic compounds when heated up. Prolonged consumption of burnt oils lead to atherosclerosis, inflammatory joint disease and development of birth defects. The scientists also questioned global health authories’ wilful recommendation of large amounts of polyunsaturated fats into the human diet without accompanying measures to ensure the protection of these fatty acids against heat-and oxidative-degradation.
Palm oil contains more saturated fats then canola oil, corn oil, linseed oil, soybean oil, safflower oil, and sunflower oil. Therefore, palm oil can withstand extreme deepfry heat and resistant to oxidation compared to vegetable oils of high unsaturated fats. Since the turn of the century, palm oil is increasingly incorporated into the global commercial food industry because it remains stable when deepfried or baked in extreme high heat and for its high levels of natural antioxidants.
Oils that are suitable for high-temperature frying (above 230 °C/446 °F) because of their high smoke point include:
- Canola oil (marketed as "rapeseed oil" or, sometimes, simply "vegetable oil" in the UK)
- Corn oil
- Mustard oil
- Olive oil, pomace
- Olive oil, extra light
- Palm oil
- Peanut oil (marketed as "groundnut oil" in the UK)
- Rice bran oil
- Safflower oil
- Sesame oil (semi-refined)
- Soybean oil
- Sunflower oil
Oils suitable for medium-temperature frying (above 190 °C/374 °F) include:
- Almond oil
- Ghee, Clarified Butter
- Cottonseed oil
- Grape seed oil
- Lard
- Diacylglycerol (DAG) oil
- Olive oil (Virgin, and refined)
- Walnut oil
- Mustard oil
Unrefined oils should not be used for frying, but are safe for simmering.
Storing and keeping oil
Whether refined or not, all oils are sensitive to heat, light and exposure to oxygen. Rancid oil has an unpleasant aroma and acrid taste, and its nutrient value is greatly diminished. To delay the development of rancid oil, a blanket of an inert gas, usually nitrogen, is applied to the vapor space in the storage container immediately after production. This is referred to as tank blanketing.
It is best to store all oils in the refrigerator or a cool, dry place. Oils may thicken, but if you let them stand at room temperature they will soon return to liquid. To prevent negative effects of heat and light, take oils out of cold storage just long enough to use them. Refined oils high in monounsaturated fats keep up to a year (olive oil will keep up to a few years), while those high in polyunsaturated fats keep about six months. Extra-virgin and virgin olive oils keep at least 9 months after opening. Other monounsaturated oils keep well up to a high eight months; unrefined polyunsaturated oils only about half as long.
In contrast, saturated oils such as coconut and palm have much longer shelf lives and can be safely stored at room temperature. This is due to their lack of polyunsaturated content.
Types of oils and their characteristics
Lighter, more refined oils tend to have higher smoke points. Experience using an oil is generally a sufficiently reliable guide. Although outcomes of empirical tests are sensitive to the qualities of particular samples (brand, composition, refinement, process), the data below should be helpful in comparing the properties of different oils.
Smoking oil indicates a risk of combustion, and left unchecked can also set off a fire alarm. When using any cooking oil, should it begin to smoke, heat should be reduced immediately . Generally, one should be fully prepared to extinguish a burning oil fire before heating, typically by having on hand the lid to place on the pan, or (for the worst case) having on hand the proper fire extinguisher.
Comparison to other types of food
Fat composition in different foods (click at right to hide or show) view • talk • edit
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