Pressing method has a long history and its technological process is relatively simple. After steaming and frying the oil, the oil is extruded mechanically. The ancient pressing method requires heavy manual labor of operators. In the extruded oil residue (oil cake), the residual oil content is quite high, which wastes extremely valuable oil resources. Modern pressing method has been industrialized and automated operation, but the problem of high residual oil content in oil residue can not be solved.
It can be distinguished from the pretreatment of crushed raw materials by cold pressing and hot pressing, also known as ripe pressing. Cold pressing means that the raw material is directly put into the mustard oil press machine
to extrude the oil without baking or steaming. In this method, the oil is relatively light in color and brighter in color, but the oil yield is low, and the flavor of the oil is not strong and mellow. The purpose of drying oil crops before pressing is to reduce the moisture content of raw materials, increase the activity and fluidity of oil molecules, thereby increasing oil yield and ensuring the fragrance of oil quality and flavor. But it also destroys the chemical composition of the oil, resulting in darker and darker oil.
The process of oil being extruded: When oil enters the chamber of the mustard oil press machine, the pressure increases with the rotation of the chamber. With the continuous extrusion of oil and grease, the direct contact of squeezed particles produces pressure on each other, which results in the plastic deformation of seeds, especially in the rupture of oil film and bonding. In this way, after being squeezed out of the chamber, the squeeze material is not loose, but a plastic body, called the oil cake. Because of the dual effects of temperature and pressure, protein will continue to deteriorate, and then affect the plasticity of the squeeze material. In a word, the proper degree of protein denaturation can ensure the best oil extraction effect.