Comparing Pressing and Solvent Extraction Methods in Oil Processing

Pressing and solvent extraction are two oil processing methods for edible oils. Pressing is a physical method that extracts oil from oilseeds by mechanical means. The process includes crushing the oilseeds,flaking, cooking, and finally pressing to squeeze out the oil. This method is simple, requires fewer supporting equipment, is adaptable to a wide range of oilseeds, is flexible in production, and produces high-quality oil with a light color and pure flavor. However, pressing leaves a high oil residue in the oil cake, resulting in lower oil extraction efficiency, high power consumption, and easy wear and tear of parts.

Solvent extraction involves soaking or spraying oil-bearing materials with a solvent to dissolve the oil. The mixture of solvent and oil is then filtered to obtain crude oil, which is processed through hydration, alkali refining, and decolorization to become edible oil that meets national standards. The evaporated solvent gas is cooled, recovered, and recycled. Solvent extraction can be divided into direct extraction and pre-pressing extraction.

Due to the low oil yield of the pressing method, the raw materials for pressing must have a high oil content and are often oil crops. Since pressing leaves a high oil residue in the oil cake, modern enterprises often use solvent extraction on the pressed oil cake to save resources and improve efficiency. Compared with pressing, solvent extraction has the advantages of high oil yield, low residual oil content in the meal (less than 1%), good meal quality, low processing cost, and low labor intensity.

Solvent extraction is suitable for most oil-bearing materials, especially those with high nutritional value but low oil yield. Due to the superiority of modern solvent extraction technology, it is widely used in oil processing, and about 90% of the world's oils are produced by this method.