Mechanical Expression of Oil

Mechanical expression of rice bran yields less oil, 10-12%, than solvent extraction, 16-18%. Rice bran is treated with steam and dried prior to pressure expression. Prepressing is usually carried out at 70 kg/cm followed by oil expulsion at 105-316 kg/cm (9). As a result of the low yield of oil from mechanical extraction, residual oil in the bran is recovered with hexane. Hexane extraction can be performed by batch or a continuous operation. Continuous operation uses countercurrent flow to improve mass transfer. Solvent extraction at high temperatures results in higher crude oil yield, but the crude oil is of lower quality. A new oil-extraction process, which involves premolding of rice bran at 14% moismre content and <40°C followed by hexane extraction at <15°C, was reported to yield a light-colored crude oil with no wax (9). 

Venter MJ, Willems P, Kuipers NJM, Haan ABd. 2006. Gas Assisted Mechanical Expression of Cocoa Butter from Cocoa Nibs and Edible Oils from Oilseeds. The Journal of Supercritical Fluids 37(3) 350-358. 

Canola Oil occurs as a light yellow oil. It is typically obtained by a combination of mechanical expression followed by n-hexane extraction, from the seed of the plant Brassica juncea, Brassica napus, or Brassica rapa (Fam. Cruciferae). The plant varieties are those producing oil-bearing seeds with a low erucic acid (C22 i) content. It is a mixture of triglycerides composed of both saturated and unsaturated fatty acids. It is refined, bleached, and deodorized to substantially remove free fatty acids phospholipids color odor and flavor components and miscellaneous, other non-oil materials. It can be hydrogenated to reduce the level of unsaturated fatty acids for functional purposes in foods. It is a liquid at 0° and above. 

Palm Kernel Oil (Unhydrogenated) is a fat obtained from the kernel of the fruit of the oil palm Elaeis guineensis Jacq. (Fam. Arecaceae) by mechanical expression or solvent extraction. It is refined, bleached, and deodorized to substantially remove free fatty acids, phospholipids, color, odor and flavor components, and miscellaneous other non-oil materials. Like coconut oil, it has a more abrupt melting range than other fats and oils. 

The modem commercial methods of oil extraction from oilseeds include (1) batch hydraulic pressing Oil seeds are expressed by hydraulic pressure to yield oil (2) continuous mechanical pressing Oil seeds are squeezed through a tapering outlet and oil is expressed by the increasing pressure and (3) solvent extraction Oil seeds are extracted with solvent followed by removal of solvent to yield oil. These methods are also employed in the extraction of sesame seeds with some modification. 

Although extraction with solvents is an effective method for the recovery of oil (or fat) from any material, it is most advantageous with materials low in oil. The minimum oil content to which oilseed press-cake can be reduced by mechanical expression is approximately the same for all oilseeds, about 2-3%. Consequently, the oil unrecoverable by mechanical expression, in terms of percentage of the total oil, increases progressively as the oil content of the material decreases. 

The PhEur 2005 describes sunflower oil as the refined fatty oil obtained from the seeds of Helianthus annus C. by mechanical expression or by extraction. A suitable antioxidant may be added. 

Sunflower oil should be labeled to indicate the name and concentration of any antioxidant added, and also whether the oil was obtained by mechanical expression or extraction. A specification for sunflower oil is contained in the Food Chemicals Codex (FCC). 

Vaziri (54) extended the Risnes model (53) by incorporating several features important to solution gas drive processes. Dissolved gas can come out of solution as the reservoir pressure is depleted below the oil bubble point/ Solution gas drive refers to oil production resulting from expansion of the gas phase. Vaziri assumed that liquid and gas form a single phase completely filling the pore space. Mechanical properties of the fluid (e.g., compressibility) vary with proportion of the gas phase and can be determined by application of Boyle s and Henry s laws. An expression for a fluid compressibility capacity, termed fluid flexibility, of the following form is used ... 

The German word verfahrenstechnik, literally to be translated as process technics, can be misunderstood easily Americans should not try to translate it. When this expression was coined prior to World War I, it was practically identical with unit operations. Now it is used by engineers to express that their methods can be applied to any type of industry such as mechanical, chemical, food, oil, and other industries. The German technical chemist by using this word means the development of a process whose core is the reactor which is decisive for the chemical conversion and thus for the whole arrangement of the plant for production cost and profitability. 

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