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Cooking oil is plant, animal, or synthetic liquid fat used in frying, baking, and other types of cooking. It is also used in food preparation and flavoring not involving heat, such as
salad dressings A salad dressing is a sauce for salads. Used on virtually all '' leafy salads'', dressings may also be used in making salads of beans (such as three bean salad), noodle or pasta salads and antipasti, and forms of potato salad. Salad dressings ...
and bread dips, and may be called 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. There are a wide variety of cooking oils from plant sources such as olive oil, palm oil,
soybean oil Soybean oil (British English: soyabean oil) is a vegetable oil extracted from the seeds of the soybean (''Glycine max''). It is one of the most widely consumed cooking oils and the second most consumed vegetable oil. As a drying oil, processe ...
, canola oil ( rapeseed oil), corn oil,
peanut oil Peanut oil, also known as groundnut oil or arachis oil, is a vegetable oil derived from peanuts. The oil usually has a mild or neutral flavor but, if made with roasted peanuts, has a stronger peanut flavor and aroma. It is often used in Americ ...
and other vegetable oils, as well as animal-based oils like
butter Butter is a dairy product made from the fat and protein components of churned cream. It is a semi-solid emulsion at room temperature, consisting of approximately 80% butterfat. It is used at room temperature as a spread, melted as a condim ...
and lard. Oil can be flavored with aromatic foodstuffs such as
herb In general use, herbs are a widely distributed and widespread group of plants, excluding vegetables and other plants consumed for macronutrients, with savory or aromatic properties that are used for flavoring and garnishing food, for medicina ...
s,
chillies Chili peppers (also chile, chile pepper, chilli pepper, or chilli), from Nahuatl '' chīlli'' (), are varieties of the berry-fruit of plants from the genus ''Capsicum'', which are members of the nightshade family Solanaceae, cultivated for t ...
or
garlic Garlic (''Allium sativum'') is a species of bulbous flowering plant in the genus '' Allium''. Its close relatives include the onion, shallot, leek, chive, Welsh onion and Chinese onion. It is native to South Asia, Central Asia and northeas ...
.
Cooking spray Cooking spray is a spray form of an oil as a lubricant, lecithin as an emulsifier, and a propellant such as food-grade alcohol, nitrous oxide, carbon dioxide or propane. Cooking spray is applied to frying pans and other cookware to prevent fo ...
is an aerosol of cooking oil.


Health and nutrition

While consumption of small amounts of saturated fats is common in diets, meta-analyses found a significant correlation between ''high consumption'' of saturated fats and blood LDL concentration, a
risk factor In epidemiology, a risk factor or determinant is a variable associated with an increased risk of disease or infection. Due to a lack of harmonization across disciplines, determinant, in its more widely accepted scientific meaning, is often u ...
for cardiovascular diseases. Other meta-analyses based on cohort studies and on controlled, randomized trials found a positive, or neutral, effect from consuming polyunsaturated fats instead of saturated fats (a 10% lower risk for 5% replacement). Mayo Clinic has highlighted certain 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 omega-3) fats like olive oil, peanut oil, canola oil, soy and cottonseed oils are generally healthier. The US National Heart, Lung and Blood Institute 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 is preferable to the consumption of palm oil for lowering the risk of heart disease. Cashew oil and other nut-based oils do not present a hazard to persons with a nut allergy, because oils are primarily lipids, and allergic reactions are due to surface proteins on the nut. The seeds of most cultivated plants contain higher levels of omega-6 fatty acids than omega-3, with some notable exceptions. Growth at colder temperatures tends to result in higher levels of omega-3 fatty acids in seed oils.


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 LDL cholesterol and lowering levels of HDL cholesterol. Trans fats from partially hydrogenated oils are more harmful than naturally occurring oils. Several large studies indicate a link between the 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. In the US, trans fats are no longer "generally recognized as safe", and cannot be added to foods, including cooking oils, without special permission.


Cooking with oil

Heating as well as heating vessel rapidly changes characteristics of cooking oil. Oils that are healthy at room temperature can become unhealthy when heated above certain temperatures, especially when heating repeatedly. The toxic risk is linked to oxidation of fatty acids and fatty acids with higher levels of unsaturation are oxidized more rapidly during heating in air.Crosby (2018) Do Cooking Oils Present a Health Risk?
/ref> So, when choosing a cooking oil, it is important to match the oil's '' heat tolerance'' with the temperature which will be used. and to change frying oil a few times per week. Deep-fat frying temperatures are commonly in the range of , less commonly, lower temperatures ≥  are used. 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
deep frying Deep frying (also referred to as deep fat frying) is a cooking method in which food is submerged in hot fat, traditionally lard but today most commonly oil, as opposed to the shallow oil used in conventional frying done in a frying pan. ...
at higher temperatures and is resistant to
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
compared to high-polyunsaturated vegetable oils. 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, and for its high levels of natural antioxidants, though the refined palm oil used in industrial food has lost most of its carotenoid content (and its orange-red color). The following oils are suitable for high-temperature frying due to their high smoke point: * Avocado oil * Mustard oil * Palm oil *
Peanut oil Peanut oil, also known as groundnut oil or arachis oil, is a vegetable oil derived from peanuts. The oil usually has a mild or neutral flavor but, if made with roasted peanuts, has a stronger peanut flavor and aroma. It is often used in Americ ...
(marketed as "groundnut oil" in the UK and India) * Rice bran oil * Safflower oil * Olive oil * Semi-refined sesame oil * Semi-refined sunflower oil Less aggressive frying temperatures are frequently used. A quality frying oil has a bland flavor, at least smoke and flash points, with maximums of 0.1% free fatty acids and 3% linolenic acid. Those oils with higher linolenic fractions are avoided due to polymerization or gumming marked by increases in viscosity with age. Olive oil resists thermal degradation and has been used as a frying oil for thousands of years.


Storing and keeping oil

All oils degrade in response to heat, light, and oxygen. To delay the onset of rancidity, a blanket of an
inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...
, 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 form if they are left 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, keep ''up to a year'', while those high in polyunsaturated fats, such as
soybean oil Soybean oil (British English: soyabean oil) is a vegetable oil extracted from the seeds of the soybean (''Glycine max''). It is one of the most widely consumed cooking oils and the second most consumed vegetable oil. As a drying oil, processe ...
, keep about six months. Rancidity tests have shown that the shelf life of
walnut oil Walnut oil is oil extracted from walnuts, '' Juglans regia''. The oil contains polyunsaturated fatty acids, monounsaturated fatty acids, and saturated fats. Composition Walnut oil is composed largely of polyunsaturated fatty acids (72% of tota ...
is about 3 months, a period considerably shorter than the ''best before'' date shown on labels. By contrast, oils high in saturated fats, such as avocado oil, have relatively long shelf lives and can be safely stored at
room temperature Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a person when they are wearing typical indoor clothing. Human comfort can extend beyond this range depending on ...
, as the low polyunsaturated fat content facilitates stability.


Types and characteristics

Cooking oils are composed of various fractions of
fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...
s. For the purpose of frying food, oils high in monounsaturated or saturated fats are generally popular, while oils high in polyunsaturated fats are less desirable. High
oleic acid Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish. In chemical terms, oleic acid is classified as a monounsaturated o ...
oils include almond, macadamia, olive, pecan, pistachio, and high-oleic cultivars of safflower and sunflower.


Smoke point

The smoke point is marked by "a continuous wisp of smoke". It is the temperature at which an oil starts to burn, leading to a burnt flavor in the foods being prepared and degradation of
nutrients A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excr ...
and
phytochemical Phytochemicals are chemical compounds produced by plants, generally to help them resist fungi, bacteria and plant virus infections, and also consumption by insects and other animals. The name comes . Some phytochemicals have been used as poison ...
s characteristic of the oil. Above the smoke point are flash and fire points. The flash point is the temperature at which oil vapors will ignite but aren't produced in sufficient quantities to stay lit. The flash point generally occurs at about . The fire point is the temperature at which hot oil produces sufficient vapors they will catch on fire and burn. As frying hours increase, all these temperature points decrease. They depend more on an oil's acidity than fatty-acid profile. The smoke point of cooking oils varies generally in association with how oil is refined: a higher smoke point results from removal of impurities and free fatty acids. Residual solvent remaining from the refining process may decrease the smoke point. It has been reported to increase with the inclusion of antioxidants (BHA, BHT, and TBHQ). For these reasons, the published smoke points of oils may vary. Oils are extracted from nuts, seeds, olives, grains or legumes by
extract An extract is a substance made by extracting a part of a raw material, often by using a solvent such as ethanol, oil or water. Extracts may be sold as tinctures, absolutes or in powder form. The aromatic principles of many spices, nuts ...
ion using industrial chemicals or by mechanical processes.
Expeller pressing Expeller pressing (also called oil pressing) is a mechanical method for extracting oil from raw materials. The raw materials are squeezed under high pressure in a single step. When used for the extraction of food oils, typical raw materials are ...
is a chemical-free process that collects oils from a source using a mechanical press with minimal heat. Cold-pressed oils are extracted under a controlled temperature setting usually below intended to preserve naturally occurring phytochemicals, such as polyphenols, tocotrienols, plant sterols and
vitamin E Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vi ...
which collectively affect color, flavor, aroma and nutrient value.


Comparison to other types of food


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 Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relative ...
. * Pressing, using an expeller press or cold press (pressing at low temperatures to prevent oil heating). *
Decanter centrifuge A centrifuge is a device that employs a high rotational speed to separate components of different densities. This becomes relevant in the majority of industrial jobs where solids, liquids and gases are merged into a single mixture and the separation ...
. 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.


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 Fuller's earth is any clay material that has the capability to decolorize oil or other liquids without the use of harsh chemical treatment. Fuller's earth typically consists of palygorskite (attapulgite) or bentonite. Modern uses of fuller's ea ...
, 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, including antioxidants such as BHA, BHT, and
tocopherol Tocopherols (; TCP) are a class of organic chemical compounds (more precisely, various methylated phenols), many of which have vitamin E activity. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rat ...
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. 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 can congeal in pipes, causing sanitary sewer overflow. 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. Placing the container of oil in the refrigerator to harden also makes disposal easier and less messy.


Recycling

Cooking oil can be recycled. It can be used in animal feed, soap, make-up, clothes, rubber, detergents, directly as fuel, and to produce
biodiesel Biodiesel is a form of diesel fuel derived from plants or animals and consisting of long-chain fatty acid esters. It is typically made by chemically reacting lipids such as animal fat ( tallow), soybean oil, or some other vegetable oi ...
. In the recycling industry, used cooking oil recovered from restaurants and food-processing industries (typically from deep fryers or griddles) is called yellow grease, recycled vegetable oil (RVO), used vegetable oil (UVO), or waste vegetable oil (WVO).Brown Grease Feedstocks for Biodiesel
. K. Shaine Tyson, National Renewable Energy Laboratory. Retrieved January 31, 2009
Grease trap A grease trap (also known as grease interceptor, grease recovery device, grease capsule and grease converter) is a plumbing device (a type of trap) designed to intercept most greases and solids before they enter a wastewater disposal system. C ...
s or interceptors collect fats and oils from kitchen sinks and floor drains. The result is called brown grease, and unlike yellow grease its severe contaminants make it much harder to recycle.


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 Garbage, trash, rubbish, or refuse is waste material that is discarded by humans, usually due to a perceived lack of utility. The term generally does not encompass bodily waste products, purely liquid or gaseous wastes, or toxic waste produ ...
. In
Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...
, thieves sell stolen electric
transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
s to operators of roadside food stalls for reuse of the oil in
deep frying Deep frying (also referred to as deep fat frying) is a cooking method in which food is submerged in hot fat, traditionally lard but today most commonly oil, as opposed to the shallow oil used in conventional frying done in a frying pan. ...
, suitable for prolonged use longer than regular cooking oil, but a threat to consumer health due to the presence of PCBs and polycyclic aromatic hydrocarbons.


References

* *


Further reading

* * Fox, R. (2001)
Frying oils
In Kaarin Goodburn (Ed.) ''EU Food Law''. Woodhead. pp. 195–224. .


External links

* {{DEFAULTSORT:Cooking Oil Food science Non-timber forest products