Soybean oil production
The production of commercial soybean oil is complicated. The mechanical production of soybean oil with hydraulic presses is not much used because it’s expensive and gives lower yields. Soybean oil is normally produced by extraction with solvents. The production consists of following steps:
Cleaning of soybeans
The soybeans are first cleaned, dried and dehulled prior to oil extraction. The soybean hulls needs to be removed because they absorb oil and give a lower yield. This de-hulling is done by cracking the soybeans and a mechanical separation of the hulls and cracked soybeans. Magnets are used to separate any iron from the soybeans.
The soybeans are also heated to about 75°C to coagulate the soy proteins to make the oil extraction easier.
Extraction of soybean oil
First the soybeans are cut in flakes which are put in a percolation extractors and immerged with a solvent, normally hexane. Counterflow 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 is 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 hexane free crude soybean oil is then further purified.
Purification of soybean oil
The crude soybean oil still contains many oil-insoluble and oil-soluble impurities that needs to be removed. 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 remove colour and other impurities.
Hydrogenation of soybean oil (optional)
This process will increase the stability of the soybean oil and will make it less liquid. However, this process will create more saturated fats and will reduce the favourable unsaturated fats. In addition, transfats are produced which can cause hearth problems. Hydrogenated soybean oil is used in foods that require more solid fat such as margarines.