What is Crushing?
In the past, crushing was done between mill stones that later became steel rollers. Hence the factories are known as oil mills and the process as oil milling or oil crushing. Seeds with a high oil content, like rape seed and sunflower seed, are usually mechanically pressed in expellers after a preheating step in indirectly heated conditioners. The expeller cake (or pressed cake) will then be further treated in the extractor, as it might still contain up to 18 per cent of oil. In some cases, the expeller cake may not be further extracted but sold as such for feed purposes.
In the expeller, the oil-bearing material is fed into one end of a cylinder within which a power-driven worm conveyor forces the material to the other end of the cylinder and out against resistance. The pressure exerted in the process squeezes out the oil.
Soybeans, which have a relatively low oil content, are thermally treated, mechanically crushed and used as raw material/flakes for further extraction.
Sometimes the raw material is pressed without heating; such oils are known as cold-pressed oils. Since cold pressing does not extract all the oil, it is practiced only in the production of a few speciality edible oils.
What is refining
The purpose of refining edible oils and fats is to remove the free fatty acids, moisture, colour pigments and other impurities while maintaining the nutritional value and ensuring the quality and stability of the end product. The crude oil is refined by neutralising and bleaching and then deodorised with steam under vacuum. There are two main refining processes - chemical/alkali refining and physical refining, which differ principally in the way the free fatty acids are removed.
Oils and fats are recognised as essential nutrients in both human and animal diets. Fats are part of a normal, balanced, healthy diet and the body needs them for a variety of reasons including provision of energy; provision of the essential fatty acids (from omega-6 and omega-3 families) which we need because our bodies cannot produce them; vitamin absorption of vitamins A, D, E and K as well as making a large contribution to the texture and palatability of foods. You can find more information on the different oils here