![Cooking oils on a shelf 02](https://upload.wikimedia.org/wikipedia/commons/f/f0/Cooking_oils_on_a_shelf_02.jpg)
Cooking oil is plant, animal, or synthetic liquid
fat
In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food.
The term often refers spec ...
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 c ...
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
frameless , right , alt = A cracked coconut and a bottle of coconut oil
Coconut oil (or coconut butter) is an edible oil derived from the wick, meat, and milk of the coconut palm fruit. Coconut oil is a white solid fat; in warmer climates duri ...
,
palm oil
Palm oil is an edible vegetable oil derived from the mesocarp (reddish pulp) of the fruit of the oil palms. The oil is used in food manufacturing, in beauty products, and as biofuel. Palm oil accounted for about 33% of global oils produced from ...
and
palm kernel oil
Palm kernel oil is an edible plant oil derived from the kernel of the oil palm tree ''Elaeis guineensis''. It is related to other two edible oils: ''palm oil'', extracted from the fruit pulp of the oil palm, and ''coconut oil'', extracted from th ...
are solid.
There are a wide variety of cooking oils from plant sources such as
olive oil
Olive oil is a liquid fat obtained from olives (the fruit of ''Olea europaea''; family Oleaceae), a traditional tree crop of the Mediterranean Basin, produced by pressing whole olives and extracting the oil. It is commonly used in cooking: f ...
,
palm oil
Palm oil is an edible vegetable oil derived from the mesocarp (reddish pulp) of the fruit of the oil palms. The oil is used in food manufacturing, in beauty products, and as biofuel. Palm oil accounted for about 33% of global oils produced from ...
,
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, processed so ...
,
canola oil
Close-up of canola blooms
Canola flower
Rapeseed oil is one of the oldest known vegetable oils. There are both edible and industrial forms produced from rapeseed, the seed of several cultivars of the plant family Brassicaceae. Historically, i ...
(
rapeseed
Rapeseed (''Brassica napus ''subsp.'' napus''), also known as rape, or oilseed rape, is a bright-yellow flowering member of the family Brassicaceae (mustard or cabbage family), cultivated mainly for its oil-rich seed, which naturally contains a ...
oil),
corn oil
Corn oil (North American) or maize oil (British) is oil extracted from the germ of corn (maize). Its main use is in cooking, where its high smoke point makes refined corn oil a valuable frying oil. It is also a key ingredient in some margarines. ...
,
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 American ...
and other
vegetable oil
Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or fat ...
s, 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 condiment ...
and
lard
Lard is a semi-solid white fat product obtained by rendering the fatty tissue of a pig.[Lard]
entry in the o ...
.
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 medicinal ...
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, Allium fistulosum, Welsh onion and Allium chinense, Chinese onion. It is native to South A ...
.
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 foo ...
is an aerosol of cooking oil.
Health and nutrition
![Sunflowerseed oil](https://upload.wikimedia.org/wikipedia/commons/7/7d/Sunflowerseed_oil.jpg)
While consumption of small amounts of
saturated fat
A saturated fat is a type of fat in which the fatty acid chains have all single bonds. A fat known as a glyceride is made of two kinds of smaller molecules: a short glycerol backbone and fatty acids that each contain a long linear or branched c ...
s is common in diets,
meta-analyses
A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting me ...
found a significant correlation between ''high consumption'' of saturated fats and blood
LDL
Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall densit ...
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 use ...
for
cardiovascular diseases
Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, ...
. Other meta-analyses based on
cohort studies
A cohort study is a particular form of longitudinal study that samples a cohort (a group of people who share a defining characteristic, typically those who experienced a common event in a selected period, such as birth or graduation), performing ...
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
The Mayo Clinic () is a nonprofit American academic medical center focused on integrated health care, education, and research. It employs over 4,500 physicians and scientists, along with another 58,400 administrative and allied health staff, ...
has highlighted certain oils that are high in saturated fats, including coconut
The coconut tree (''Cocos nucifera'') is a member of the palm tree family ( Arecaceae) and the only living species of the genus ''Cocos''. The term "coconut" (or the archaic "cocoanut") can refer to the whole coconut palm, the seed, or the ...
, palm oil
Palm oil is an edible vegetable oil derived from the mesocarp (reddish pulp) of the fruit of the oil palms. The oil is used in food manufacturing, in beauty products, and as biofuel. Palm oil accounted for about 33% of global oils produced from ...
and palm kernel oil
Palm kernel oil is an edible plant oil derived from the kernel of the oil palm tree ''Elaeis guineensis''. It is related to other two edible oils: ''palm oil'', extracted from the fruit pulp of the oil palm, and ''coconut oil'', extracted from th ...
. 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 oil
Cottonseed oil is cooking oil from the seeds of cotton plants of various species, mainly ''Gossypium hirsutum'' and ''Gossypium herbaceum'', that are grown for cotton fiber, animal feed, and oil.
Cotton seed has a similar structure to other oi ...
s are generally healthier. The US National Heart, Lung and Blood Institute
The National Heart, Lung, and Blood Institute (NHLBI) is the third largest Institute of the National Institutes of Health, located in Bethesda, Maryland, United States. It is tasked with allocating about $3.6 billion in FY 2020 in tax revenue to ...
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
Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, hea ...
.
Cashew oil
The cashew tree (''Anacardium occidentale'') is a tropical evergreen tree native to South America in the genus ''Anacardium'' that produces the cashew seed and the cashew apple accessory fruit. The tree can grow as tall as , but the dwarf cult ...
and other nut-based oils do not present a hazard to persons with a nut allergy
A tree nut allergy is a hypersensitivity to dietary substances from tree nuts and edible tree seeds causing an overreaction of the immune system which may lead to severe physical symptoms. Tree nuts include, but are not limited to, almonds, Brazil ...
, 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
Omega-6 fatty acids (also referred to as ω-6 fatty acids or ''n''-6 fatty acids) are a family of polyunsaturated fatty acids that have in common a final carbon-carbon double bond in the ''n''-6 position, that is, the sixth bond, counting from ...
than omega-3
Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chem ...
, 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
Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pla ...
by raising levels of LDL
Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall densit ...
cholesterol and lowering levels of HDL cholesterol. Trans fats from partially hydrogenated oils
Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic c ...
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
The National Heart, Lung, and Blood Institute (NHLBI) is the third largest Institute of the National Institutes of Health, located in Bethesda, Maryland, United States. It is tasked with allocating about $3.6 billion in FY 2020 in tax revenue to ...
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
Health, according to the World Health Organization, is "a state of complete physical, mental and social well-being and not merely the absence of disease and infirmity".World Health Organization. (2006)''Constitution of the World Health Organiza ...
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?](_blank)
/ref>
So, when choosing a cooking oil, it is important to match the oil's ''heat tolerance
Plant breeding is process of development of new cultivars. Plant breeding involves development of varieties for different environmental conditions – some of them are not favorable. Among them, heat stress is one of such factor that reduces the pr ...
'' 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
Palm oil is an edible vegetable oil derived from the mesocarp (reddish pulp) of the fruit of the oil palms. The oil is used in food manufacturing, in beauty products, and as biofuel. Palm oil accounted for about 33% of global oils produced from ...
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. Norm ...
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 a d ...
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
The smoke point, also referred to as the burning point, is the temperature at which an oil or fat begins to produce a continuous bluish smoke that becomes clearly visible, dependent upon specific and defined conditions. Smoke point values can va ...
:
* Avocado oil
Avocado oil is an Vegetable oil, edible oil extracted from the pulp of avocados, the fruit of ''Persea americana''. It is used as an edible oil both raw and for cooking, where it is noted for its high smoke point. It is also used for lubrication a ...
* Mustard oil
Mustard oil can mean either the pressed oil used for cooking, or a pungent essential oil also known as volatile oil of mustard. The essential oil results from grinding mustard seed, mixing the grounds with water, and extracting the resulting vol ...
* Palm oil
Palm oil is an edible vegetable oil derived from the mesocarp (reddish pulp) of the fruit of the oil palms. The oil is used in food manufacturing, in beauty products, and as biofuel. Palm oil accounted for about 33% of global oils produced from ...
* 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 American ...
(marketed as "groundnut oil" in the UK and India)
* Rice bran oil
Rice bran oil is the oil extracted from the hard outer brown layer of rice called bran. It is known for its high smoke point of and mild flavor, making it suitable for high-temperature cooking methods such as stir frying and deep frying. It is p ...
* Safflower oil
Safflower (''Carthamus tinctorius'') is a highly branched, herbaceous, thistle-like annual plant in the family Asteraceae. It is commercially cultivated for vegetable oil extracted from the seeds and was used by the early Spanish colonies along ...
* Olive oil
Olive oil is a liquid fat obtained from olives (the fruit of ''Olea europaea''; family Oleaceae), a traditional tree crop of the Mediterranean Basin, produced by pressing whole olives and extracting the oil. It is commonly used in cooking: f ...
* Semi-refined sesame oil
Sesame oil is an edible vegetable oil derived from sesame seeds. The oil is one of the earliest-known crop-based oils. Worldwide mass modern production is limited due to the inefficient manual harvesting process required to extract the oil. O ...
* Semi-refined sunflower oil
Sunflower oil is the non-volatile oil pressed from the seeds of the sunflower (''Helianthus annuus''). Sunflower oil is commonly used in food as a frying oil, and in cosmetic formulations as an emollient.
Sunflower oil is primarily composed ...
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
Rancidification is the process of complete or incomplete autoxidation or hydrolysis of fats and oils when exposed to air, light, moisture, or bacterial action, producing short-chain aldehydes, ketones and free fatty acids.
When these processes oc ...
, 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
Tank blanketing, also referred to as tank padding, is the process of applying a gas to the empty space in a storage tank, storage container. The term storage container here refers to any container that is used to store products, regardless of its s ...
.
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
Macadamia oil (or macadamia nut oil) is the non-volatile oil collected from the nuts of the macadamia (''Macadamia integrifolia''), a native Australian plant. It is used in food as a frying or salad oil, and in cosmetic formulations as an emollien ...
, 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, processed so ...
, 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 total ...
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
Avocado oil is an Vegetable oil, edible oil extracted from the pulp of avocados, the fruit of ''Persea americana''. It is used as an edible oil both raw and for cooking, where it is noted for its high smoke point. It is also used for lubrication a ...
, 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, fr ...
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 omega ...
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 excret ...
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 poisons ...
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, h ...
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
Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some of ...
, tocotrienols
The vitamin E family comprise four tocotrienols (alpha, beta, gamma, delta) and four tocopherols (alpha, beta, gamma, delta). The critical chemical structural difference between tocotrienols and tocopherols is that tocotrienols have unsaturated is ...
, plant sterols
Phytosterols are phytosteroids, similar to cholesterol, that serve as structural components of biological membranes of plants. They encompass plant sterols and stanol ester, stanols. More than 250 sterols and related compounds have been identified ...
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 vitami ...
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, relatively ...
.
* Pressing, using an expeller
Expeller pressing (also called oil pressing) is a mechanical method for extracting oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes w ...
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 rats, i ...
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
Sanitary sewer overflow (SSO) is a condition in which untreated sewage is discharged from a sanitary sewer into the environment prior to reaching sewage treatment facilities. When caused by rainfall it is also known as wet weather overflow. Cause ...
.
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 oil with ...
.
In the recycling industry, used cooking oil recovered from restaurants and food-processing industries (typically from deep fryer
A deep fryer (also referred to as a deep fat fryer), is a kitchen appliance used for deep frying. Deep frying is a method of cooking by submerging food into oil at high heat, typically between temperatures of .
While commonly used in commercia ...
s or griddle
A griddle, in the UK also called a girdle, is a cooking device consisting mainly of a broad, usually flat cooking surface. Nowadays it can be either a movable metal pan- or plate-like utensil, a flat heated cooking surface built into a stove or ...
s) is called yellow grease, recycled vegetable oil (RVO), used vegetable oil (UVO), or waste vegetable oil (WVO).[Brown Grease Feedstocks for Biodiesel](_blank)
. 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. Co ...
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
Gutter oil, trench oil, or sewer oil (, or ) is a Chinese slang term for recycled oil.
It can be used to describe the illicit practice of restaurants reusing cooking oil that has already been cooked with longer than safety codes permit. It can ...
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 produc ...
.
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 stall A food kiosk or food booth (also food stand, temporary food service facility) is generally a temporary structure used to prepare and sell food to the general public, usually where large groups of people are situated outdoors in a park, at a parade ...
s 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. Norm ...
, suitable for prolonged use longer than regular cooking oil, but a threat to consumer health due to the presence of PCBs
Polychlorinated biphenyls (PCBs) are highly carcinogenic chemical compounds, formerly used in industrial and consumer products, whose production was banned in the United States by the Toxic Substances Control Act in 1979 and internationally by t ...
and polycyclic aromatic hydrocarbons
A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. P ...
.
References
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Further reading
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* Fox, R. (2001)
Frying oils
In Kaarin Goodburn (Ed.) ''EU Food Law''. Woodhead. pp. 195–224. .
External links
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{{DEFAULTSORT:Cooking Oil
Food science
Non-timber forest products