Corn oil extraction is not an isolated event in any corn-based refinery. Thus the process of oil extraction goes along with other processes like production of starch, corn sweeteners etc. Basic step for all these processes is inspection and cleaning. The shipments are inspected for contamination and cleaned thrice to remove cob parts, dust, chaff and foreign materials before steeping, the first processing step begins. In this step of steeping, clean corn grains are soaked at 50°C water for 30-40 hours in big steel tanks called steep tank. During this process the grains swell and soften. After steeping, the corn is coarsely ground to break the germ loose from other components. The ground corn, in water slurry, flows to the germ separators. In this process of germ separation, cyclone separators spin the low density corn germ out of the slurry. The germs are pumped into a screen and washed separately to remove stray amount of starch in the mixture. Oil is recovered from corn germ by expelling, solvent extraction or a combination of expelling and solvent extraction. Wet milled germ is preferably expelled from an oil content of 50-60% down to 20-25% and finally extracted with hexane to a residual oil content of 1-2% in the spent corn germ flakes. The oil is then refined and filtered into finished corn oil. The germ residue is saved and used as a component of animal feeds. The starch component of the grain is further processed to give a number of products.

Crude corn oil contains 95% triglycerides besides containing minor compounds like free fatty acids, waxes, phospholipids, pigments, and odourous compounds. Before making the corn oil acceptable to the consumers these components are removed from the crude oil through a refining process. This process involves several steps: (i) formation of sodium soaps of the free fatty acids, (ii) removal of the emulsion containing the soaps and phospholipids by centrifugation, (iii) removal of waxes by chilling, (iv) removal of pigments by contact with bleaching clays, (iv) removal of odours by high-vacuum distillation at 225°C to 260°C. The fatty acid fraction is recovered by.heating the emulsion in the presence of sulphuric acid and is sold as an ingredient for use in beef and poultry rations.