Keyword: refining, chemical, physical 

The aim of refining process is to reduce the free fatty acid content and to remove other gross impurities such as phosphatides, proteinaceous and mucilagenous substances present in crude oils. The process is normally carried out on vegetable oils as animal fats, are usually not refined. The most common method of refining is by treatment of the fat or oil with an alkali solution, i.e. chemical refining. This results in a large reduction of free fatty acids through their conversion into water-soluble soaps. Phosphatides, proteinaceous and mucilagenous substances are soluble in the oil only in an anhydrous form and upon hydration with the caustic or other refining solution are readily separated. Oils low in phosphatide content such as palm and coconut oils, on the other may undergo physical refining, i.e. by the use of stripping steam to distil off the more volatile impurities.