Vegetable Oils Refining is necessary for vegetable oils and fats so they can be used for cooking and frying foods.
Vegetable Oils Refining is necessary for vegetable oils and fats so they can be used for cooking and frying foods. Vegetable oils are obtained from a variety of seeds, grains and nuts. Most common types of oil bearing seeds and nuts are Rice bran, cotton seed, Palm, Palm kernel, Peanut, Soyabean, Sunflower, Cottonseed, Rapeseed. Other major specialty oils are obtained from Almond, cashew, shea, walnut, etc.
Vegetable Oils and fats have impurities such as moisture, solids(insolubles), Gums(lecithins), Free Fatty Acids(FFA), waxes and compounds of sodium, potassium, magnesium, calcium, and other metals. These impurities must be removed to improve the functionality of the oils. Other characteristics of oils (such as Color, odor, and taste) are also considered impurities by modern consumers. These impurities are removed in a series of steps such as degumming (to remove gums), neutralizing (to remove FFA), bleaching (to remove color), deodorizing (to remove odor and taste), and dewaxing or winterization (to remove waxes).
In Chemical Refining, Vegetable Oil is treated with caustic lye for separation of free fatty acids from oil. This is a conventional process that can be applied to all oils. A byproduct of alkali refining is soap-stock, which is used for manufacture of low quality washing soap. Alternately, the soap-stock can be treated with acid to recover fatty acids. The waste-water from refinery requires extensive treatment. This can be avoided by alternate Physical Refining process.
In Physical Refining, Vegetable Oil is subject to distillation to remove free fatty acids. The alkali treatment is completely avoided. This reduces the amount of waste water and eliminates production of soap. This process is becoming more popular.
The purpose of Degumming Vegetable Oils is to remove Gums. All oils have hydratable and non-hydratable gums.
a. Water Degumming: Hydratable gums are removed by treating oils with water and separating the gums. The gums can be dried to produce lecithin.
b. Acid Degumming: Non-Hydratable gums are removed by treating oils with acids and separating the gums.
The purpose of Neutralizing Vegetable Oils is to remove Free-Fatty Acids (FFAs). Traditionally, FFAs are treated with caustic soda (NaoH). The reaction produces Soaps which are separated from the oil. Because trace amounts of soaps remain in the oil, the oil is either washed with water or treated with Silica.
Some processors prefer not to perform caustic neutralizing. Instead, they prefer Physical Refining in which the FFAs are evaporated from the oil under high temperature and vacuum. This process can be combined with deodorization step described under FFA stripping.
Physical Refining process is preferred because (a) it does not produce soaps; (b) it recovers fatty acids that provide better cost recovery; (c) there is smaller yield loss compared to caustic refining—especially for oils with higher FFAs; and (d) it is a chemical-free process.
The purpose of Bleaching is to remove color pigments contained in Vegetable Oils. The oil is treated with Bleaching Clays that adsorb the color pigments. The clay is filtered and the clean bleached oil is stored for further processing. Process flow diagram is attached.
The purpose of Deodorizing Vegetable Oils is to remove odor substances. The oil is subjected to steam distillation under high temperature and vacuum to evaporate all odor substances. The resulting deodorized oil is almost bland and tasteless.
As mentioned previously, the Deodorizing equipment can be modified to achieve Physical Refining. Since the conditions for deodorization and physical refining are almost identical, the modified equipment can be employed to achieve deodorization as well as physical refining.
Fatty-Acids are evaporated (distilled) in FFA Stripping. The Fatty-Acid vapors are condensed by direct contact with liquid Fatty-Acids to recover the evaporated Fatty-Acids. The distillation and condensation of Fatty-Acids is accomplished under very high vacuum to lower the boiling point of Fatty-Acids and prevent them from oxidizing.
The purpose of dewaxing Vegetable Oils is to remove waxes especially in those oils that contain waxes. Such oils are subjected to chilling and filtration to remove waxes and other high melting point substances.
Winterizing is also used to separate the unsaturated fats from unsaturated fats—especially in Palm Oil or other saturated fats. The chilling process solidifies the saturated fats; thus enabling separation via filtration.