Expeller pressing

Expeller pressing (also called oil pressing) is a mechanical method for extracting oil from raw materials. The raw materials are squeezed under high pressure in a single step. When used for the extraction of food oils, typical raw materials are nuts, seeds and algae, which are supplied to the press in a continuous feed. As the raw material is pressed, friction causes it to heat. In the case of harder nuts (which require higher pressures) the material can exceed temperatures of . An expeller press is a screw-type machine that mainly presses oil seeds through a caged barrel-like cavity. Some other materials used with an expeller press include meat by-products, synthetic rubber and animal feeds. Raw materials enter one side of the press and waste products exit the other side. The machine uses friction and continuous pressure from the screw drive to move and compress the seed material. The oil seeps through small openings that do not allow seed fiber solids to pass. Afterward, the seeds are formed into a hardened press cake, which is removed from the machine. Pressure involved in expeller pressing creates heat in the range of . Raw materials are typically heated up to to make the pressing more efficient, otherwise the pressing itself will heat the oil to . Some companies claim that they use a cooling apparatus to reduce this temperature to protect certain properties of the oils being extracted. Expeller processing cannot remove every last trace of liquid (usually oil) from the raw material. A significant amount remains trapped inside the cake remaining after pressing. In most small-scale rural situations this is of little importance, as the remaining cake after oil extraction finds uses in local dishes, in the manufacture of secondary products, or in animal feed. Some raw materials do not release oil by expelling, the most notable being rice bran. To remove oil from commodities that do not respond to expelling or to extract the final traces of oil after expelling, it is necessary to use solvent extraction.