An expeller press is a continuous screw-type machine that compresses oilseeds under high mechanical pressure to expel oil, producing both a crude oil stream and a solid press cake without the use of chemical solvents.
In trade practice
The press is set up with a specific screw configuration and die opening to suit each seed type; sunflower and rapeseed require different settings. Friction generated during compression raises the temperature of the oil and cake, which must be monitored when a cold-pressed designation is claimed. Buyers sourcing expeller-pressed oil for food use typically request a certificate of analysis covering free fatty acid content, peroxide value and moisture. Residual solvent is not a concern with expeller pressing, which simplifies the analytical panel compared with solvent-extracted oils.
In a specification
A contract for expeller-pressed oil specifies the seed variety, whether the press was run under temperature-controlled conditions, and the maximum free fatty acid level permitted in the crude oil as delivered.