The production of commercial soybean oil is complicated. It's expensive and gives lower yields to use the mechanical production of soybean oil with hydraulic presses. So soybean oil is normally produced by extraction with solvents. The production of soybean oil consists of following steps:
Cleaning of soybeans
Firstly, the soybeans are cleaned, dried and dehulled before oil extraction. The soybean hulls absorb oil and give a low yield, so they need to be removed by the huller through cracking the soybeans and a mechanical separation of the hulls and cracked soybeans. At the same time, magnets are used to separate any iron from the soybeans. In order to make the oil extraction easier, the soybeans are also heated to coagulate the soy proteins.
Extraction of soybean oil
During this process, the soybeans are cut in flakes which are put in percolation extractors and immerged with a solvent, normally hexane. Counter flow is used as extraction system because it gives the highest yield. After removing the hexane, the extracted flakes only contain about 1% of soybean oil and are used as livestock meal or to produce food products such as soy protein. The hexane is separated from the soybean oil in evaporators. The evaporated hexane is recovered and returned to the extraction process. The soybean oil is then further purified.
Purification of soybean oil
The crude soybean oil still contains many oil-insoluble and oil-soluble impurities that need to be refining. The oil-insoluble material are removed with filtration and the soluble materials is removed with different processes including degumming (removing of phosphatides), alkali refining (washing with alkaline solution to remove free fatty acids, colorants, insoluble matter and gums) and bleaching (with activated earth or activated carbon to bleach and remove other impurities).
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