Cooking oil

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 flavoring that doesn't involve 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, although some oils that contain saturated fat, such as coconut oil, palm oil and palm kernel oil, are solid at room temperature.

Types of cooking oil include: olive oil, avocado oil, palm oil, soybean oil, canola oil (rapeseed oil), pumpkin seed oil, corn oil, sunflower oil, safflower oil, peanut oil, grape seed oil, sesame oil, argan oil, rice bran oil and other vegetable oils.

Oil can be flavoured with aromatic foodstuffs such as herbs, chillies or garlic.

Health and nutrition

Olive oil

Italian olive oil

Sunflowerseed oil

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 fewer 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, initial meta-analyses (1997, 2003) found a high correlation between high consumption of such fats and coronary heart disease. Surprisingly, however, more recent meta-analyses (2009, 2010), based on cohort studies and on controlled, randomized trials, find a positive or neutral effect from shifting consumption from carbohydrate to saturated fats as a source of calories, and only a modest advantage for shifting from saturated to polyunsaturated fats (10% lower risk for 5% replacement).

Mayo Clinic has highlighted oils that are high in saturated fats, including 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, avocado, safflower, corn, sunflower, soy, mustard 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 monounsaturated oils while soybean and sunflower oils are rich with polyunsaturated fat. Results of research carried out in Costa Rica in 2005 suggest that consumption of non-hydrogenated unsaturated oils like soybean and sunflower are preferable to the consumption of palm oil.

Not all saturated fats have negative effects on cholesterol. Some studies indicate that 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. Further, it has been reported that palm oil consumption reduces blood cholesterol in comparison with other traditional sources of saturated fats such as coconut oil, dairy and animal fats.

Saturated fat is required by the body and brain to function properly. In fact, one study in Brazil compared the effects of soybean oil to coconut oil (a highly saturated fat) and found that while both groups showed a drop in BMI, the soybean oil group showed an increase in overall cholesterol (including a drop in HDL, the good cholesterol). The coconut oil group actually showed an increase in the HDL:LDL ratio (meaning there was more of the good cholesterol), as well as smaller waist sizes (something that was not shown in the soybean oil group.

In 2007, scientists Kenneth C. Hayes and Pramod Khosla of Brandeis University and Wayne State University indicated that the focus of current research has shifted from saturated fats to individual fats and percentage of fatty acids (saturates, monounsaturates, polyunsaturates) in the diet. 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.

Oils high in unsaturated fats may help to lower "bad" LDL cholesterol and may also raise "good" HDL cholesterol, though these effects are still under study.

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 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.

A 2001 parallel review of 20-year dietary fat studies in the United Kingdom, the United States of America, and Spain found that polyunsaturated oils like soya, canola, sunflower, and corn oil degrade easily to toxic compounds when heated. Prolonged consumption of burnt oils led to atherosclerosis, inflammatory joint disease, and development of birth defects. The scientists also questioned global health authorities' recommendation that large amounts of polyunsaturated fats be incorporated 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 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. 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.

Oils that are suitable for high-temperature frying (above 230 °C (446 °F)) because of their high smoke point

• Refined Avocado oil
• Corn oil
• Mustard oil
• Palm oil
• Peanut oil (marketed as "groundnut oil" in the UK and India)
• Rice bran oil
• Safflower oil
• Semirefined Sesame oil
• Soybean oil
• Semirefined Sunflower Oil

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. Vitamin E oil is a natural antioxidant that can also be added to cooking oils to prevent rancidification.

All oils should be kept in a cool, dry place. Oils may thicken, but they will soon return to liquid if they stand at room temperature. To prevent negative effects of heat and light, oils should be removed from cold storage just long enough for use. 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 eight months, while unrefined polyunsaturated oils will keep only about half as long.

In contrast, saturated oils, such as coconut oil and palm oil, have much longer shelf lives and can be safely stored at room temperature. Their lack of polyunsaturated content causes them to be more stable.

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.

Type of oil or fat	Saturated	Monounsaturated	Polyunsaturated	Smoke point	Uses
Almond oil	8%	64%	28%	221 °C (430 °F)	Baking, sauces, flavoring
Avocado oil	14%	71%	15%	249 °C (480 °F)	Frying, sautéing,baking, barbecuing (naturally refined avocado only - not applicable to virgin avocado oil) dipping oil, salad oil
Butter	66%	30%	4%	177 °C (351 °F)	Cooking, baking, condiment, sauces, flavoring
Ghee, clarified butter	65%	32%	3%	190–250 °C (374–482 °F)	Deep frying, cooking, sautéeing, condiment, flavoring
Canola oil	8%	64%	28%	204 °C (399 °F)	Frying, baking, salad dressings
Coconut oil	86%	13%	1%	177 °C (351 °F)	Commercial baked goods, candy and sweets, whipped toppings, nondairy coffee creamers, shortening
Rice bran oil	20%	47%	33%	254 °C (489 °F)	Cooking, frying, deep frying, salads, dressings. Very clean flavoured & palatable.
Corn oil	13%	25%	62%	236 °C (457 °F)	Frying, baking, salad dressings, margarine, shortening
Cottonseed oil	24%	26%	50%	216 °C (421 °F)	Margarine, shortening, salad dressings, commercially fried products
Flaxseed oil	8%	21%	71%	107 °C (225 °F)
Grape seed oil	8%	21%	71%	252 °C (486 °F)	Cooking, salad dressings, margarine
Hemp oil	9%	12%	79%	166 °C (331 °F)	Cooking, salad dressings, ...
Lard	41%	47%	2%	182–204 °C (360–399 °F)	Baking, frying
Margarine, hard	80%	14%	6%	150 °C (302 °F)	Cooking, baking, condiment
Mustard oil	13%	60%	21%	254 °C (489 °F)	Cooking, frying, deep frying, salads, dressings. Very clean flavoured & palatable.
Margarine, soft	20%	47%	33%	150–160 °C (302–320 °F)	Cooking, baking, condiment
Macadamia oil	14%	84%	2%	196 °C (385 °F)	Cooking, frying, deep frying, salads, dressings. A slightly nutty odour.
Diacylglycerol (DAG) oil	3.5%	37.95%	59%	215 °C (419 °F)	Frying, baking, salad oil
Olive oil (extra virgin)	7%	78%	15%	208 °C (406 °F)	Cooking, salad oils, margarine
Olive oil (virgin)	14%	73%	11%	215 °C (419 °F)	Cooking, salad oils, margarine
Olive oil (refined)	14%	73%	11%	225 °C (437 °F)	Sautee, stir frying, deep frying, cooking, salad oils, margarine
Olive oil (extra light)	14%	73%	11%	242 °C (468 °F)	Sautee, stir frying, frying, deep frying, cooking, salad oils, margarine
Palm oil	52%	38%	10%	230 °C (446 °F)	Cooking, flavoring, vegetable oil, shortening
Peanut oil	11%	71%	18%	231 °C (448 °F)	Frying, cooking, salad oils, margarine
Pumpkin seed oil	8%	36%	57%	121 °C (250 °F)	salad oils
Safflower oil	7%	78%	15%	265 °C (509 °F)	Cooking, salad dressings, margarine
Sesame oil (Unrefined)	14%	43%	43%	210 °C (410 °F)	Cooking
Sesame oil (semi-refined)	14%	43%	43%	232 °C (450 °F)	Cooking, deep frying
Soybean oil	15%	24%	61%	241 °C (466 °F)	Cooking, salad dressings, vegetable oil, margarine, shortening
Sunflower oil	11%	78%	11%	226 °C (439 °F)	Cooking
Tea seed oil	22%	60%	18%	252 °C (486 °F)	Cooking, salad dressings, stir frying, frying, margarine
Walnut (Semi-refined)	15%	21%	64%	204 °C (399 °F)	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.

Cooking oil producers targeting the health food market often use cold press extraction only, as it provides an extraction process free of chemical solvents and high temperatures. This process is generally referred to as "naturally refined"

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 oil but not in water, 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 tempuratures 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. 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. These unrefined oils must be cared for properly in order to avoid increased instability from heat, air and light. Smoke point of virgin, unrefined oils is often much lower than advertised due to the instability of the product. Health food markets will often also sell "naturally refined, expeller pressed" versions of cooking oils. These oils have not been processed using chemicals or extreme temperatures. The result is a healthy, stable cooking oil with increased smoke point and suitability for high heat cooking.

Waste cooking oil

A bin for spent cooking oil in Austin, Texas, USA, managed by a recycling company.

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. Also, oil can congeal on pipes provoking blockages.

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.

Cooking oil can be recycled. It can be used to produce soap and biodiesel.

See also

• Cooking spray
• Vegetable fats and oils
• Toxic oil syndrome
• Gutter oil

References

• O'Brien, R.D. (1998). Fats and Oils: Formulating and Processing for Applications. Lancaster, PA: Technomic Publishing Co., Inc. ISBN 0-8493-1599-9.
• Potter, N.N. and J.H. Hotchkiss (1995). Food Science (Fifth ed.). New York: Chapman & Hall. pp. 359–80, 402–7. ISBN 0-442-01398-1.

Further reading

• Fox, R. (2001). Frying oils. In Kaarin Goodburn (Ed.) EU Food Law. Woodhead. pp. 195–224. ISBN 978-1-85573-557-6.

External links

• American Oil Chemical Society official website
• Food Oil Smoke Points from the Canola Council
• Review of Nutritional Attributes of Cold Pressed Hemp Seed Oil from King's College London
• Algae: Another way to grow edible oils