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.

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 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, 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.

WASTE COOKING OIL

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.

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