Vegetable oil refining is necessary for vegetable oils & fats or animal oils & fats so they can be used for cooking and frying foods. The crude oil obtained from cooking oil press machine or solvent extraction plant contains impurities.
Vegetable oil refining machine helps to remove impurities to make the edible oil, more palatable and stable against rancidity upon storage. The process of removing these impurities is called refining.Refining of vegetable oils is essential to ensure removal of Gums, Waxes, Phosphatides and Free Fatty Acids (F.F.A.) from the oils.
Dry degumming is widely applied in refining low phosphatide oil such as edible oil, or used for preparing oils for further physical refining. Gums are removed through precipitation by acid conditioning and via filtration in the bleaching process, rather than centrifugal separation. It is a well-proven degumming method featured of cost effective.
Dry degumming process of edible oil: For crude edible oil refining plant, drying degumming process is suggested. Classically, crude edible oil is first mixed with about 0.05– 0.1% concentrated phosphoric acid. Then, after a short retention time, about 1 or 2% acid-activated bleaching earth is added under vacuum at a temperature of 80–120℃. After a suitable contact time, the spent degumming is removed by filtration. Phosphoric acid is mainly used by edible oil refiners especially in world, due to economical reasons. However, citric acid is also used in some cases. The critical factor affecting the quality of refined edible oil is the introduced amount of acid. Either over or under dosage can lead to darkening and offflavor problems of the edible oil.
Except dry degumming, there are also other types of degumming methods applied in vegetable oil refining plant, such as water degumming and acid degumming. The main differences between these types lie in processing method and chemicals used. Besides, the selection degumming method is based on the content of phosphatides in the crude oil.
Water Degumming: Water degumming is suggested for refining crude oil with phosphorus content around 200ppm, such as soybean oil. The crude oil is firstly go through precipitatation by pure water hydration. Then gums are removed from the crude oil by using the principle of centrifugal separation. Water is the key agent in this degumming process.
Acid degumming: Through acid conditioning process, gums are precipitated from the crude oil and then be removed by centrifugal separation. It is normally used in refining process of rice bran and sunflower oil.