Cooking oil is a plant, animal, or synthetic liquid 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 may be called edible oil.
Read Pritish Kumar Halder blog, cooking oil, its health and nutrition benefit. Also discussed is its extraction process.
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 is 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. Cooking spray is an aerosol of cooking oil.
Health and nutrition
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 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. 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 170–190 °C (338–374 °F), less commonly, lower temperatures ≥ 130 °C (266 °F) 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 at higher temperatures and is resistant to oxidation 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:
Peanut oil (marketed as “groundnut oil” in the UK and India)
Rice bran 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 200 °C (392 °F) smoke and 315 °C (599 °F) 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.
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.
There are three broad types of oil extraction:
1)Chemical solvent extraction, most commonly using hexane.
2)Pressing, using an expeller press or cold press (pressing at low temperatures to prevent oil heating).
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 can either be unrefined or refined using one or more of the following refinement processes (in any combination):
1)Distilling, which heats the oil to evaporate off chemical solvents from the extraction process.
2)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.
3)Neutralization, or deacidification, which treats the oil with sodium hydroxide or sodium carbonate to pull out free fatty acids, phospholipids, pigments, and waxes.
4)Bleaching, which removes “off-coloured” components by treatment with fuller’s earth, activated carbon, or activated clays, followed by heating, filtering, then drying to recoup the oil.
5)Dewaxing, or winterizing, improves clarity of oils intended for refrigeration by dropping them to low temperatures and removing any solids that form.
6)Deodorizing, by treating with high-heat pressurized steam to evaporate less stable compounds that might cause “unusual” odors or tastes.
7)Preservative addition, including antioxidants such as BHA, BHT, and tocopherol to help preserve oils that have been made less stable due to high-temperature processing.
Filtering, a non-chemical process that 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.