Vegetable oil can be extracted from oil seeds by several different methods, including solvent extraction, expeller method, and supercritical extraction. To maximize extraction efficiency, oil seeds are usually "crushed," thus decreas­ing particle size and lowering the mass transfer resistances of oil removal. The traditional method for extraction is using an expeller machine, of which there are two variations: a screw type and a ram type. Solvent extraction is a more recent method, and usually utilizes a petroleum-based product such as hexane. Expeller methods are typically used for edible products such as nutrients and food oils, whereas solvent extraction is for more modern oil applications. Supercritical extraction is used for extraction of value-added nutrient and medicinal ingredients from oil seeds and is still in the develop­ment stage. Typical oil extraction efficiency by these methods is shown in Table 2.2. However, it should be noted that the actual efficiency depends on the specific type of oil seeds, specific design of the machinery used, specific extraction conditions employed, the moisture level of raw materials, and dif­ferent operational parameters.

Global Production/Consumption of Vegetable Oils3

Source: aOilseeds: World Markets and Trade, Foreign Agricultural Service, USDA, and Economic Research Service. Oil Crops Yearbook. U. S. Department of Agriculture.

Note: The worldwide production data for 2008-2009 are forecast values.