| Plant oils |
|---|
 |
| Types |
| Uses |
| Components |
| Types offats infood |
|---|
| Components |
| Manufactured fats |
Plant oils or vegetable oils areoils derived from plant sources, as opposed toanimal fats orpetroleum. 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 are what are most commonly calledvegetable oils. These aretriglyceride-based, and include cooking oils likecanola oil, solid oils likecocoa butter, oils used inpaint likelinseed oil 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 thescrew 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, calledseed cake, are either discarded or used for other purposes.[1] Oil presses can be either manual or powered. The second type of oil press is theram 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 atMIT'sD-Lab, for example, is capable of exerting 800–1,000psi to extract peanut oil.[2]
Industrial machines for extracting oil mechanically are callexpellers. 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".[3]
In modern vegetable oil production, oils are usually extracted chemically, using asolvent such ashexane. 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.[4]
Macerated orinfused oils are oils to which other matter has been added, such as herbs or flowers. Typically, the oil used is a food-gradefat-type oil.
Essential oils are not true oils but volatile aromatic compounds that are used in flavors, fragrances, and inaromatherapy for health purposes. Essential oils are usually extracted bydistillation.
Maceration is also used as a means of extracting essential oils.[5] 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.