Expeller pressing

Expeller pressing (also called oil pressing) is a mechanical method for extracting oil from raw materials trademarked by Anderson International Corp. Mr. Valerius D. Anderson founded the V. D. Anderson Company in Cleveland, Ohio in 1888. In 1900, Mr. V. D. Anderson created the first successful continuously operated Expeller® press. 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 up; in the case of harder nuts (which require higher pressures) the material can exceed temperatures of 120 °F (49 °C).

An expeller press is a screw-type machine that mainly presses oil seeds through a caged barrel-like cavity. Other materials used with an expeller press include but are not limited to 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 drives to move and compress the seed material. The oil seeps 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 140–210 °F (60–99 °C). 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 of the cake left over after pressing. In most small-scale rural situations this is of little or no importance, as the cake that remains after the oil has been removed finds uses in local dishes, in the manufacture of secondary products, or for animal feed. Some raw materials, however, do not release oil by simple expelling, the most notable being rice bran. In order 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.

The earliest expeller presses utilized a continuous screw design. The compression screws were much like the screws of a screw conveyor—that is, the helicoid flighting started at one end and ended at the other.

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