Crude oils often cannot meet the requirements of various applications directly and require further refining to improve their stability, color, and flavor. Refining is a multi-step purification process, mainly including:
* Degumming: Removing water-soluble gums, primarily phospholipids, from crude oils. This is usually done by adding hot water or dilute acid to hydrate and coagulate the gums, which are then removed by sedimentation or centrifugation.
* Deacidification: Neutralizing and removing free fatty acids from oils. The most common method is alkali refining, which involves adding an appropriate amount of alkali solution to the oil to saponify the free fatty acids and form soapstock, which is then removed by centrifugation. This step is crucial for improving the taste and extending the shelf life of oils.
* Decolorization: Improving the color of oils. Using adsorbents such as activated clay and activated carbon, under heating and stirring conditions, pigments (such as chlorophyll and carotenoids) and other trace impurities in the oil are adsorbed. The adsorbent is then separated from the oil using filtration equipment.
* Deodorization: Removing unpleasant odors and volatile substances from oils. Under high temperature and high vacuum conditions, steam is introduced into the oil, and the principle of steam distillation is used to remove low-boiling-point off-odor substances and residual free fatty acids. Deodorization significantly improves the flavor and smoke point of the oil.
Refined animal fats become clearer, lighter in color, purer in flavor, and more stable, making them suitable for a wider range of food processing or industrial applications.
