Edible/vegetable oil refining is a step by step process. Refining oil removes phospholipids, pigments, off-flavors, free fatty acids and other impurities. The entire oil refining plant process comprises degumming/neutralization, bleaching, deoderization, and winterization. Chemical refining is performed in order to remove the fatty acids from the crude oil that is extracted from the seeds. These 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, another method that is used for edible oil refining is physical refining. Through this method, the free fatty acids are removed through the process of distillation in one stage of deodorizing. In order to come up with effective results, the crude oil should be thoroughly degummed. This is not applicable with some oil like the oil extracted from cottonseeds. All kinds of refining methods are done with the help of various equipment and machinery, and are used to refine almost all kinds of oil extracted from oil seeds like sunflower seeds, linseeds, groundnuts, sesame seeds, and mustard seeds, etc.
Physical and chemical refining is defined according to the technology used. Physical refining means the removal of gum in 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 is then separated by centrifuges.