how to refine edible oil

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Edible oils are extracted from various sources including sunflowers, soybeans, cottonseeds, groundnuts, palms, mustard seeds rice bran and olives. Edible oil refining process involves strict step-by-step procedures which should be followed adequately. The various processes include:

Degumming:

Degumming is the initial step in edible oil refining process. Degumming can either be pure water degumming, enzymatic degumming or chemical degumming.
  • Water Degumming
This is the initial phase of the edible oil refining process. Oils have hydratable phosphatides that take in water. After being hydrated they become oil-insoluble and can be centrifuged to separate. The water degummed gums are processed into lecithin the required end product needed by consumers. Water degumming has certain shortcomings. There are increased oil losses, increased costs of refining and possible impurities and wastes in the refined oil.
  • Enzymatic Degumming
It was developed by Indian Institute of Chemical Technology. It involves the use of enzymes to act on certain specific impurity molecules in the oil such as phosphorus hence increasing precision in oil refinery. It can be dry, partial or full enzymatic degumming. With the world’s turning into green energies such as biodiesel, enzymatic degumming is taking the centre stage in the refining process.

small edible oil refinery

Alkali Refining (Neutralization)

This method has existed for centuries and is one of the most popular refinery techniques. An alkali solution is used to treat fats and oils. The free fatty acids in the oils and fats are responsible for acidity in the oil and alkali is used to remove them. The free fatty acids derived from this process are converted into soaps which are then separated via separators due to their water soluble nature. Phospholipids, proteins and carbohydrates can also be hydrated into water soluble substances. The treated oils and fats are then passed through a vacuum dryer to get rid of moisture. Generally, Alkali refining involves heating edible oil at specific optimal temperatures, conditioning, neutralization, washing and vacuum drying.

Bleaching

The alkali treated oil is then bleached to remove any traces of soap, iron, phospholipids and carotenes. These contents are undesirable. Bleaching process involves the addition of clay absorbent to remove colors and impurities like chlorophyll, residual soap and gums and metal traces. Strict parameters on moisture levels, temperature, contact time and vacuum must be followed accordingly. Filtration is then carried out to get the final oil product.

Dewaxing/ Winterization

This procedure is use to clear refined edible oils so as to meet cloud point specifications. It involves effective crystallization and filtration methods. Homogenizers, crystallizers and self-filters are used enhanced by a good cooling system.

Physical refining

Physical refining involves removal of free fatty acid by use of steam distillation technique. Physical refining is a very important step in edible oil refining process since it creates a fatty acid free and odorless product with light hue and stability from possible oxidation. This is done under warm temperatures and high vacuum. The simplest way to carry out physical refining process and in an economical manner is to subject the oil through a series of compartments intermittently. These compartments should be placed horizontally and vertically and with continuous steam supply. The oil is subjected to this steam under high vacuum. All volatiles such as fatty acids, ketones, alcohols, coloring agents and aldehydes are removed from the oil. The process should be monitored through instruments with precision on key variables like temperatures, vacuum and time. This is followed by deodorization.
refined edible oil

Deodorization

Deodorization is used to get rid of unacceptable odor through vacuum stripping using steam distillation. Steam is a good stripping agent. Through steam distillation, the odorous molecules and compounds are stripped off aided by injection of steam into heated oil under low pressure. Volatile off-flavors in bleached edible oil and the ones formed in this thermally intensive process are removed. Deodorization procedure is time specific and should operate at optimal time. Deodorizing edible oil for too long can take off the essential flavors in the oil and deodorizing for a short time can retain unwanted precursors and flavors leading to unwanted flavors during storage.

Fractionation

Dry fractionation is the last step in edible oil refining process. Fractionation is used to separate edible oils into two major components, Olein and Stearin. Olein and stearin are yielded in this process. The process does not require addition of extra external agents or components. The process is carried out either in a continuous rotary vacuum drum filter and plate with frame filter or through crystallization method which develops and grows particle sizes for easy and swish separation of stearin and Olein.The process entails preheating edible oil to attain uniformity and homogeneity and eliminating any solid or semisolid zones. Crystallization is then carried out to allow the oils to be passed through membrane filters thus separating solid from liquid.
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