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What is Expeller Pressing?
Expeller pressing is the method of extracting oil with a mechanical press rather than utilizing a chemical extraction process. An expeller press is a screw type machine, which presses oil seeds through a caged barrel-like cavity. This machine uses friction and continuous pressure from the screw drives to move and compress the seed material. The oil seeds through small openings that do not allow seed fiber solids to pass through. Afterward, the pressed seeds are formed into a hardened cake, which is removed from the machine. Pressure involved in expeller pressing creates heat in the range of 140-210º F (60-99º C).Advantage and Disadvantages of the Expeller Pressing Method
Expellers can be used with almost any kind of oilseeds and nuts. The process is relatively simple and not capital-intensive. While the smallest solvent extraction plant would have a processing capacity of 100-200 tons per day, expellers are available for much smaller capacities, from a few tons per day and up.There are no solvent (chemical) residues in oil that has been expeller pressed resulting in a cleaner more pure oil, higher in natural colors and flavors. The process of extraction is the critical quality difference between oils often found in the natural foods marketplace as opposed to mass market or supermarket brands.
The main disadvantage of the expeller pressing method is its relatively low yield of oil recovery. Even the most powerful presses cannot reduce the level of residual oil in the press-cake below 3 to 5%. In the case of oil-rich seeds such as sesame or peanuts this may still be acceptable. Furthermore, most of the oil left in the cake can be recovered by a stage of solvent extraction. Such two stage processes (pre-press/solvent extraction) are now widely applied.
