Edible/vegetable oil refining is a step by step process. Refining removes phospholipids, pigments, off-flavors, free fatty acids and other impurities in the crude oil. The entire oil refining plant process comprises degumming/neutralization, bleaching, deodorization, and winterization.
Chemical refining is performed in order to remove the fatty acids from the crude oil which are further neutralized with the use of caustic soda. This results in the removal of sodium soaps by batch settling or centrifugal separators. The neutral oils are then bleached and deodorized.
Apart from chemical refining, physical refining is another method that used for edible oil refining. Through this method, the free fatty acids are removed during the process of distillation, which is one stage of deodorizing. The crude oil should be thoroughly degummed to come up with effective results. This is not applicable to some oil such as cottonseed oil. With the help of various equipment and machinery, all kinds of refining methods are done and used to refine almost all kinds of oil from seeds like sunflower seeds, linseeds, groundnuts, sesame seeds, and mustard seeds, etc.
More simply, physical and chemical refining is defined according to the technology used. Physical refining means the removal of gum from oil via the process of degumming, a special method for removing FFA in the process of deodorization by steam. Chemical refining, however, means chemically removing FFA (acid-base neutralization). Gum and soap produced in the last step are then separated by centrifuge.