Cooking oil
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Cooking oil is plant, animal, or synthetic fat used in frying, baking, and other types of cooking. It is also used in food preparation and flavouring not involving heat, such as salad dressings and bread dips, and in this sense might be more accurately termed edible oil.
Cooking oil is typically a liquid at room temperature, although some oils that contain saturated fat, such as coconut oil, palm oil and palm kernel oil are solid.[1]
There are a wide variety of cooking oils from plant sources such as olive oil, palm oil, soybean oil, canola oil (rapeseed oil), corn oil, peanut oil and other vegetable oils, as well as animal-based oils like butter and lard.
Oil can be flavoured with aromatic foodstuffs such as herbs, chillies or garlic.
Contents
Health and nutrition
The appropriate amount of fat as a component of daily food consumption is established as a guideline by regulatory agencies such as the FDA which recommends that 10% or fewer of calories consumed daily should be from saturated fat and 20-35% of total daily calories come from polyunsaturated and monounsaturated fats.[2]
While consumption of small amounts of saturated fats is common in diets,[3] meta-analyses found a significant correlation between high consumption of saturated fats and blood LDL concentration,[4] a risk factor for cardiovascular diseases.[5] Other meta-analyses based on cohort studies and on controlled, randomized trials found a positive[6] or neutral[7] effect from shifting consumption from saturated fats to polyunsaturated fats (10% lower risk for 5% replacement).[7]
Mayo Clinic has highlighted oils that are high in saturated fats, including coconut, palm oil and palm kernel oil. Those having lower amounts of saturated fats and higher levels of unsaturated (preferably monounsaturated) fats like olive oil, peanut oil, canola oil, soy and cottonseed oils are generally healthier.[8] The US National Heart, Lung and Blood Institute[9] urged saturated fats be replaced with polyunsaturated and monounsaturated fats, listing olive and canola oils as sources of healthier monounsaturated oils while soybean and sunflower oils as good sources of polyunsaturated fats. One study showed that consumption of non-hydrogenated unsaturated oils like soybean and sunflower are preferable to the consumption of palm oil for lowering the risk of heart disease.[10]
Peanut, cashew and other nut-based oils may present a hazard to persons with a nut allergy.
Trans fats
Unlike other dietary fats, trans fats are not essential, and they do not promote good health.[11] The consumption of trans fats increases one's risk of coronary heart disease[12] by raising levels of "bad" LDL cholesterol and lowering levels of "good" HDL cholesterol.[13] Trans fats from partially hydrogenated oils are more harmful than naturally occurring oils.[14]
Several large studies[15][16][17][18] 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 limiting the intake of trans fats.
Cooking with oil
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.[19]
Palm oil contains more saturated fats than canola oil, corn oil, linseed oil, soybean oil, safflower oil, and sunflower oil. Therefore, palm oil can withstand the high heat of deep frying and is resistant to oxidation compared to highly unsaturated vegetable oils.[20] Since about 1900, palm oil has been increasingly incorporated into food by the global commercial food industry because it remains stable in deep frying or in baking at very high temperatures[21][22] and for its high levels of natural antioxidants.[23]
Oils that are suitable for high-temperature frying (above 230 °C or 446 °F) because of their high smoke point:
- Avocado oil
- Mustard oil
- Palm oil
- Peanut oil (marketed as "groundnut oil" in the UK and India)
- Rice bran oil
- Safflower oil
- Semi-refined sesame oil
- Semi-refined sunflower oil[24]
Storing and keeping oil
All oils degrade in response to heat, light, and oxygen.[25] To delay the development of rancidity, a blanket of an inert gas, usually nitrogen, is applied to the vapor space in the storage container immediately after production, a process called tank blanketing.
In a cool, dry place, oils have greater stability, but may thicken, although they will soon return to liquid if they stand at room temperature. To minimize the degrading effects of heat and light, oils should be removed from cold storage just long enough for use. Refined oils high in monounsaturated fats, such as macadamia oil,[25] keep up to a year, while those high in polyunsaturated fats keep about six months. Rancidity tests show that the life of walnut oil is about 3 months, a period considerably shorter than the "best before" duration shown on labels.[25]
In contrast, saturated oils, such as avocado oil, have relatively long shelf lives and can be safely stored at room temperature, as their lower polyunsaturated content facilitates stability.[25]
Types of oils and their characteristics
Lighter, more refined oils tend to have a higher smoke point. 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.[citation needed]
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, reduce the heat immediately. The cook should be fully prepared to extinguish a burning oil fire before beginning to heat the oil, by having on hand the lid to place on the pan, or (for the worst case) having on hand the proper fire extinguisher.
| Type of oil or fat | Saturated | Monounsaturated | Polyunsaturated | Omega-3 | Omega-6 | Smoke point [note 1] |
Uses | |
|---|---|---|---|---|---|---|---|---|
| Almond | 8% | 66% | 26% | 0 | 17% | 221 °C (430 °F) | Baking, sauces, flavoring | |
| Avocado oil | 12% | 74% | 14% | 0.95% | 12% | 271 °C (520 °F) | Frying, sautéing, dipping oil, salad oil | |
| Butter | 66% | 30% | 4% | 0.3% | 2.7% | 150 °C (302 °F) | Cooking, baking, condiment, sauces, flavoring | |
| Ghee, clarified butter | 65% | 32% | 3% | 0 | 0 | 190–250 °C (374–482 °F) | Deep frying, cooking, sautéing, condiment, flavoring | |
| Canola oil | 6% | 62% | 32% | 9.1% | 18% | 204 °C (399 °F) | Frying, baking, salad dressings | |
| Coconut oil, (virgin) | 92% | 6% | 2% | 0 | 1.8% | 177 °C (351 °F) | Cooking, tropical cuisine, beauty products | |
| Rice bran oil | 20% | 47% | 33% | 1.6% | 33% | 254 °C (489 °F) | Cooking, frying, deep frying, salads, dressings. Very clean flavoured & palatable. | |
| Corn oil | 13% | 25% | 62% | 1.1% | 53% | 236 °C (457 °F) | Frying, baking, salad dressings, margarine, shortening | |
| Cottonseed oil | 24% | 26% | 50% | 0.2% | 50% | 216 °C (421 °F) | Margarine, shortening, salad dressings, commercially fried products | |
| Flaxseed oil (Linseed oil)[28] | 11% | 21% | 68% | 53% | 13% | 107 °C (225 °F)[29] | Salad dressings, nutritional supplement | |
| Grapeseed oil | 12% | 17% | 71% | 0.1% | 69% | 204 °C (399 °F) | Cooking, salad dressings, margarine | |
| Hemp oil | 9% | 12% | 79% | 18% | 55% | 165 °C (329 °F) | Cooking, salad dressings | |
| Lard | 41% | 47% | 2% | 1% | 10% | 138–201 °C (280–394 °F) | Baking, frying | |
| Margarine, hard | 80% | 14% | 6% | 2% | 22% | 150 °C (302 °F)[note 2] | Cooking, baking, condiment | |
| Mustard oil | 13% | 60% | 21% | 5.9% | 15% | 254 °C (489 °F) | Cooking, frying, deep frying, salads, dressings. Very clean flavoured & palatable. | |
| Margarine, soft | 20% | 47% | 33% | 2.4% | 23% | 150–160 °C (302–320 °F) | Cooking, baking, condiment | |
| Macadamia oil | 12.5% | 84% | 3.5% | 0 | 2.8% | 210 °C (410 °F) | Cooking, frying, deep frying, salads, dressings. A slightly nutty odour. | |
| Diacylglycerol (DAG) oil | 3.05% | 37.95% | 59% | 0 | - | 215 °C (419 °F) | Frying, baking, salad oil | |
| Olive oil (extra virgin) | 14% | 73% | 11% | 0.7% | 9.8% | 190 °C (374 °F) | Cooking, salad oils, margarine | |
| Olive oil (virgin) | 14% | 73% | 11% | 0.7% | 9.8% | 215 °C (419 °F) | Cooking, salad oils, margarine | |
| Olive oil (refined) | 14% | 73% | 11% | 0 | 0 | 225 °C (437 °F) | Sautee, stir frying, deep frying, cooking, salad oils, margarine | |
| Olive oil (extra light) | 14% | 73% | 11% | 0 | 0 | 242 °C (468 °F) | Sautee, stir frying, frying, deep frying, cooking, salad oils, margarine | |
| Palm oil | 52% | 38% | 10% | 0.2% | 9.1% | 230 °C (446 °F) | Cooking, flavoring, vegetable oil, shortening | |
| Peanut oil / groundnut oil | 18% | 49% | 33% | 0 | 31% | 231 °C (448 °F) | Frying, cooking, salad oils, margarine | |
| Pumpkin seed oil | 8% | 36% | 57% | 0% | 64% | 121 °C (250 °F) | salad oils | |
| Safflower oil | 10% | 13% | 77% | 0 | 74% | 265 °C (509 °F) | Cooking, salad dressings, margarine | |
| Sesame oil (Unrefined) | 14% | 43% | 43% | 0.3 | 41% | 177 °C (351 °F) | Cooking | |
| Sesame oil (semi-refined) | 14% | 43% | 43% | 0.3 | 41% | 232 °C (450 °F) | Cooking, deep frying | |
| Soybean oil | 15% | 24% | 61% | 6.7% | 50% | 241 °C (466 °F) | Cooking, salad dressings, vegetable oil, margarine, shortening | |
| Sunflower oil (linoleic, refined) | 11% | 20% | 69% | 0% | 56% | 246 °C (475 °F) | Cooking, salad dressings, margarine, shortening | |
| Sunflower oil (high oleic, refined)[30] | 9% | 82% | 9% | 0.2% | 3.6% | 225 °C (437 °F) | Cooking | |
| Tea seed oil[31] | 22% | 60% | 18% | 0.7% | 22% | 252 °C (486 °F) | Cooking, salad dressings, stir frying, frying, margarine | |
| Walnut oil (Semi-refined) | 9% | 23% | 63% | 10% | 53% | 204 °C (399 °F)[32] | Salad dressings, added to cold dishes to enhance flavor |
Cooking oil extraction and refinement
Cooking oil extraction and refinement are separate processes. Extraction first removes the oil, typically from a seed, nut or fruit. Refinement then alters the appearance, texture, taste, smell, or stability of the oil to meet buyer expectations.
Extraction
There are three broad types of oil extraction:
- Chemical solvent extraction, most commonly using hexane.
- Pressing, using an expeller press or cold press (pressing at low temperatures to prevent oil heating).
- Decanter centrifuge.
In large-scale industrial oil extraction you will often see some combination of pressing, chemical extraction and/or centrifuging in order to extract the maximum amount of oil possible.[38]
Refinement
Cooking oil can either be unrefined, or refined using one or more of the following refinement processes (in any combination):
- Distilling, which heats the oil to evaporate off chemical solvents from the extraction process.
- Degumming, by passing hot water through the oil to precipitate out gums and proteins that are soluble in water but not in oil, then discarding the water along with the impurities.
- Neutralization, or deacidification, which treats the oil with sodium hydroxide or sodium carbonate to pull out free fatty acids, phospholipids, pigments, and waxes.
- Bleaching, which removes "off-colored" components by treatment with fuller's earth, activated carbon, or activated clays, followed by heating, filtering, then drying to recoup the oil.
- Dewaxing, or winterizing, improves clarity of oils intended for refrigeration by dropping them to low temperatures and removing any solids that form.
- Deodorizing, by treating with high-heat pressurized steam to evaporate less stable compounds that might cause "unusual" odors or tastes.
- Preservative addition, such as BHA and BHT to help preserve oils that have been made less stable due to high-temperature processing.
Filtering, a non-chemical process which screens out larger particles, could be considered a step in refinement, although it doesn't alter the state of the oil.
Most large-scale commercial cooking oil refinement will involve all of these steps in order to achieve a product that's uniform in taste, smell and appearance, and has a longer shelf life.[38] Cooking oil intended for the health food market will often be unrefined, which can result in a less stable product but minimizes exposure to high temperatures and chemical processing.
Waste cooking oil
Proper disposal of used cooking oil is an important waste-management concern. Oil is lighter than water and tends to spread into thin and broad membranes which hinder the oxygenation of water. Because of this, a single litre of oil can contaminate as much as 1 million litres of water.[citation needed] Also, oil can congeal on pipes provoking blockages.[39]
Because of this, cooking oil should never be dumped in the kitchen sink or in the toilet bowl. The proper way to dispose of oil is to put it in a sealed non-recyclable container and discard it with regular garbage.[40] Placing the container of oil in the refrigerator to harden also makes disposal easier and less messy.
Recycling
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Cooking oil can be recycled. It can be used as animal feed, directly as fuel, and to produce biodiesel,[41] soap, and other industrial products.
In the recycling industry, used cooking oil recovered from restaurants and food-processing industries (typically from deep fryers or griddles) is called recycled vegetable oil (RVO), used vegetable oil (UVO), waste vegetable oil (WVO), or yellow grease.[42]
Yellow grease is used to feed livestock, and to make soap, make-up, clothes, rubber, detergents, and biodiesel fuel.[43][44]
Used cooking oil, besides being converted to biodiesel, can be used directly in modified diesel engines and for heating.
Grease traps or interceptors collect fats and oils from kitchen sinks and floor drains which would othewise clog sewer lines and interfere with septic systems and sewage treatment. The collected product is called brown grease in the recycling industry.[42] Brown grease is contaminated with rotted food solids and considered unsuitable for re-use in most applications.
Adulteration
Gutter oil and trench oil are terms used in China to describe recycled oil processed to resemble virgin oil, but containing toxic contaminants and sold illegally for cooking; its origin is frequently brown grease from garbage.[45]
In Kenya, thieves sell transformer oil stolen from electric transformers to operators of roadside food stalls for use in deep frying, suitable for prolonged use longer than regular cooking oil, but a threat to consumer health due to the presence of PCBs.[46]
Notes
- ↑ The smoke point of an oil depends primarily on its free fatty acid content (FFA) and molecular weight. Through repeated use, as in a deep fryer, the oil accumulates food residues or by-products of the cooking process, that lower its smoke point further. The values shown in the table must therefore be taken as approximate, and are not suitable for accurate or scientific use.[26][27]
- ↑ The smoke point of margarine varies depending on the types of oils used in its formulation, but can be generally assumed to be similar to that of butter.[citation needed]
References
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- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ The Nurses' Health Study (NHS)
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- ↑ 25.0 25.1 25.2 25.3 Lua error in package.lua at line 80: module 'strict' not found.
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- ↑ A. G. Vereshagin and G. V. Novitskaya (1965) The triglyceride composition of linseed oil. Journal of the American Oil Chemists' Society 42, 970-974. [1]
- ↑ http://www.goodeatsfanpage.com/collectedinfo/oilsmokepoints.htm
- ↑ Sunflowernsa.com
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ nutritiondata.com → Oil, vegetable, sunflower Retrieved on September 27, 2010
- ↑ USDA → Basic Report: 04042, Oil, peanut, salad or cooking Retrieved on January 16, 2015
- ↑ nutritiondata.com → Egg, yolk, raw, fresh Retrieved on August 24, 2009
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
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- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 42.0 42.1 Brown Grease Feedstocks for Biodiesel. K. Shaine Tyson, National Renewable Energy Laboratory. Available from Northeast Regional Biomass Program. Retrieved January 31, 2009
- ↑ Murphy, Denis J. Plant lipids: biology, utilisation, and manipulation. Wiley-Blackwell, 2005, p. 117.
- ↑ Radich, Anthony Biodiesel Performance, Costs, and Use
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
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Further reading
- Lua error in package.lua at line 80: module 'strict' not found.
- Fox, R. (2001). Frying oils. In Kaarin Goodburn (Ed.) EU Food Law. Woodhead. pp. 195–224. ISBN 978-1-85573-557-6.
