Gas assisted oilseed pressing

Recently oils from rapeseed and soybeans have gained increased importance in the alimentary sector and as regenerative energy source. Therefore, new technologies for enhanced oilseed expression are becoming increasingly interesting. In conventional seed oil production oil is recovered by mechanical solid–fluid separation using a screw press and/or by continuous solvent extraction with hexane (M. Bockisch, Handbuch der Lebensmitteltechnologie: Nahrungsfette und -Öle, Verlag Eugen Ulmer, Stuttgart, 1993, M. Bockisch, Fats and Oils Handbook, AOCS Press, Illinois, 1998). The new process of gas assisted oilseed pressing is a mechanical solid–fluid separation aided by the application of a dense gas. The gas is contacted with the oilseed before or during pressing in order to achieve lower residual oil contents. Different experimental studies could demonstrate the effectiveness of gas assisted oil pressing, especially using carbon dioxide. In uniaxial pressing experiments oil yield could be increased from 27% to as much as 71%.1 Against this background the omission of the solvent extraction step becomes a worthwhile option. It has been attempted to prove theoretically and experimentally the predominant effects, which can be divided into dissolution related and gas flow related effects. It became clear that the dominance of one mechanism or another depends on processing conditions, particularly residence time and dimension of the press cake.