Plant oils or vegetable oils are

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) and lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...

s derived from plant sources, as opposed to

animal fat Animal fats are lipids derived from animals which are used by the animal for a multitude of functions, or can be used by humans for dietary, sanitary, and cosmetic purposes. Depending on the temperature of the fat, it can change between a solid s ...

s or

petroleum Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...

. There are three primary types of plant oil, differing both the means of extracting the relevant parts of the plant, and in the nature of the resulting oil: #

Vegetable fats and oils Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of edible plants. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed ...

were historically extracted by putting part of the plant under

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

, squeezing out the oil. # Macerated oils consist of a base oil to which parts of plants are added. #

Essential oil An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the ...

s are composed of volatile aromatic compounds, extracted from plants by

distillation Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixt ...

Vegetable fats and oils

are what are most commonly called ''vegetable oils''. These are

triglyceride A triglyceride (from '' tri-'' and '' glyceride''; also TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids. Triglycerides are the main constituents of body fat in humans and other vertebrates ...

-based, and include cooking oils like

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. Historical ...

, solid oils like

cocoa butter Cocoa butter, also called theobroma oil, is a pale-yellow, edible Vegetable oil, fat extracted from the cocoa bean (''Theobroma cacao''). It is used to make chocolate, as well as some ointments, toiletries, and pharmaceuticals. Cocoa butter h ...

, oils used in

paint Paint is a material or mixture that, when applied to a solid material and allowed to dry, adds a film-like layer. As art, this is used to create an image or images known as a painting. Paint can be made in many colors and types. Most paints are ...

linseed oil Linseed oil, also known as flaxseed oil or flax oil (in its edible form), is a colorless to yellowish oil obtained from the dried, ripened seeds of the flax plant (''Linum usitatissimum''). The oil is obtained by pressing, sometimes followed by ...

and oils used for industrial purposes. Pressed vegetable oils are extracted from the plant containing the oil (usually the seed), using one of two types of oil press. The most common is the ''screw press'', which consists of a large-diameter metal screw inside a metal housing. Oil seeds are fed into the housing, where the screws mash the seeds, and create pressure which forces the oil out through small holes in the side of the press. The remaining solids, called ''seed cake'', are either discarded or used for other purposes. Oil presses can be either manual or powered. The second type of oil press is the ''ram press'', where a piston is driven into a cylinder, crushing the seeds and forcing out the oil. Ram presses are generally more efficient than screw presses. There has been recent interest in improving the design of mechanical oil presses, particularly for use in developing countries. A press developed at

MIT The Massachusetts Institute of Technology (MIT) is a private research university in Cambridge, Massachusetts, United States. Established in 1861, MIT has played a significant role in the development of many areas of modern technology and sc ...

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D-Lab
for example, is capable of exerting 800–1,000psi to extract peanut oil. Industrial machines for extracting oil mechanically are call ''expellers''. Many expellers add heat and pressure, in order to increase the amount of oil extracted. If the temperature does not exceed 120 °F, the oil can be called "cold-pressed". In modern vegetable oil production, oils are usually extracted chemically, using a

solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

such as

hexane Hexane () or ''n''-hexane is an organic compound, a straight-chain alkane with six carbon atoms and the molecular formula C6H14. Hexane is a colorless liquid, odorless when pure, and with a boiling point of approximately . It is widely used as ...

. Chemical extraction is cheaper and more efficient than mechanical extraction, at a large scale, leaving only 0.5–0.7% of the oil in the plant solids, as compared to 6–14% for mechanical extraction.

Macerated oils

Macerated or ''infused oils'' are oils to which other matter has been added, such as herbs or flowers. Typically, the oil used is a food-grade fat-type oil.

Essential oils

Essential oils are not true oils but volatile aromatic compounds that are used in flavors, fragrances, and in

aromatherapy Aromatherapy is a practice based on the use of aromatic materials, including essential oils and other aroma compounds, with claims for improving psychological well-being. It is used as a complementary therapy or as a form of alternative medic ...

for health purposes. Essential oils are usually extracted by

. Maceration is also used as a means of extracting essential oils. In this process, used, for example, to extract the onion, garlic, wintergreen and bitter almond essential oil, the plant material is macerated in warm water to release the volatile compounds in the plant.

References

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Vegetable fats and oils

Macerated oils

Essential oils

References

See also