Here is an extract from this site (http://blog.sejalvora.com/2010/10/25/the-truth-about-refined-cooking-oil/):
Refining:
Oil refining is a process where crude oils; i.e. natural oils from vegetables are refined to remove any substances that may contribute to off flavor, off odor, undesirable color, or for keeping standardization, and standardization is required because if 100 million tons are being sold, there would be chaos at the supermarket if every bottle would be different in color and clarity as it is naturally supposed to be.
Step 1: “Washing” of oil using water, salts and acids in order to remove waxes, phosphates and other impurities.
Step 2: Oil undergoes a neutralization process. Alkali which is soap mixed with oil and heated to 180F. A separator then removes the soap from the oil.
Step 3: The oil is subjected to “physical” refinement to remove odor compounds by vacuum steam distillation process.
Step 4: Next the oil is subjected to cooling. By doing this, some fats will crystallize and are removed using filtration.
Step 5: The oil is then bleached. This process stabilized the oil. Bleaching involves using clay to remove color and impurities from the oil. Oil is bleached by heating it to 130F, and mixing with clay. The mixture is held for several minutes and then the hot oil is filtered from the clay and cooled.
Step 6: Hydrogenation process is completed by pumping pressurized hydrogen into an agitated tank filled with oil. This must be done in the presence of a catalyst metal, such as nickel. Hydrogenation is done at 204C and pressure of 60psig.
Refining:
Oil refining is a process where crude oils; i.e. natural oils from vegetables are refined to remove any substances that may contribute to off flavor, off odor, undesirable color, or for keeping standardization, and standardization is required because if 100 million tons are being sold, there would be chaos at the supermarket if every bottle would be different in color and clarity as it is naturally supposed to be.
Step 1: “Washing” of oil using water, salts and acids in order to remove waxes, phosphates and other impurities.
Step 2: Oil undergoes a neutralization process. Alkali which is soap mixed with oil and heated to 180F. A separator then removes the soap from the oil.
Step 3: The oil is subjected to “physical” refinement to remove odor compounds by vacuum steam distillation process.
Step 4: Next the oil is subjected to cooling. By doing this, some fats will crystallize and are removed using filtration.
Step 5: The oil is then bleached. This process stabilized the oil. Bleaching involves using clay to remove color and impurities from the oil. Oil is bleached by heating it to 130F, and mixing with clay. The mixture is held for several minutes and then the hot oil is filtered from the clay and cooled.
Step 6: Hydrogenation process is completed by pumping pressurized hydrogen into an agitated tank filled with oil. This must be done in the presence of a catalyst metal, such as nickel. Hydrogenation is done at 204C and pressure of 60psig.