Oil extraction by pressing uses mechanical force to squeeze oil out of raw materials. This process mainly involves physical changes like material deformation, oil separation, frictional heating, and moisture evaporation. However, due to temperature, moisture, and microorganisms, biochemical changes such as protein denaturation and enzyme inactivation also occur.

During pressing, raw material particles are squeezed together, causing the liquid and gel parts to separate. The oil is extracted from the gaps in the raw material, and the particles form a hard oil cake. The effectiveness of oil extraction depends on the structure of the raw material and pressing conditions. The structure and selection of the oil press equipment also affect efficiency. The raw material's structure depends on pre-treatment quality and the oilseed's composition. Pressing conditions like pressure, time, temperature, material layer thickness, and oil discharge resistance are key factors.

Factors affect the effectiveness of oil extraction by pressing

1. Moisture Content of the Raw Material

As moisture content increases, the raw material's plasticity also increases. Optimal moisture content, or "critical moisture," ensures the best oil extraction. This range is narrow and depends on other factors like temperature and protein deformation. In practice, optimal moisture needs adjustment based on actual conditions. Too high or low moisture content can cause problems with the oil press, affecting oil discharge and residue.

2. Temperature of the Raw Material

Heating increases the raw material's plasticity, while cooling reduces it. Temperature affects plasticity, oil extraction efficiency, and the quality of oil and cake. There is an "optimal range" for temperature. In practice, increasing temperature reduces moisture content and vice versa. Too high or low temperatures cause similar issues as moisture content variations, affecting oil discharge and residue.

3. Degree of Protein Denaturation

Excessive protein denaturation reduces plasticity, increasing the required pressure for oil extraction. Proper protein denaturation is necessary for effective oil extraction, indicating the extent of colloidal structure destruction in the oilseed. During pressing, temperature and pressure continue to denature proteins. Appropriate protein denaturation ensures good oil extraction efficiency.