What are the differences in the operating procedures of different oil presses?

vegetable oils, as an important source of human nutrition, has many kinds and different chemical constituents. From protein-rich soybeans to oily peanuts, from hard soybeans to soft rapeseed, the physical properties, chemical composition and oil content of these different oils directly dictate the different operating requirements of oil presses. This diversity not only requires highly adaptable oil presses, but also drives the development of oil extraction processes. Different oil processing process, pressing process and equipment parameters are differentiated in this paper, which provides practical guidance for the industry.

 

Comparison Core Pretreatment Steps

Pre-treatment is the primary step in the oil extraction process, which directly affects oil yield and product quality. The pretreatment process of different oilseeds vary widely:

· Soybeans: washed → Crush → softened (Moisture 10-12%, ≤ 60°C) → stirred → steamed (temperature 120 -180°C). Softening soybeans reduces elasticity and improves cooking and baking efficiency.

Peanuts: Shell → crush → bake (temperature 120 -150°C) → peel, skipping softening steps. Peanut kernels are high in oil, so baking directly destroys cell structure and promotes oil release.

Canola: Soften before peeling (Moisture 8-9%, 60-70°C). Oil content is high and the risk of drum adhesion needs to be controlled. Rapeseed skin is thin, high in oil and softened to prevent adhesion when peeling. Cottonseed: peeling → softening (10-12% moisture, 60°C) → peeling. High humidity vapour is required to reduce gossypol. Cottonseed contain gossypol toxins and require high high-humidity steam detoxification to detoxify.

Critical variance analysis

1.Smash Particle Size: Soybeans require secondary smashing with particle size ≤ 0.5mm to improve cooking efficiency. Peanut kernels are crushed and baked directly, which requires less granularity.

2.Softening required: Low-oil oilseeds (such as soybeans) must be softened to reduce elasticity, while high-oil oilseeds (such as peanuts) can skip the softening step.

3.Impurity Control: Cotton seeds require to be stripped of fat to prevent equipment from clogging up, while rapeseed needs to be cleaned of sludge to avoid affecting oil quality.

 

High-Oil Content Oilseeds (e.g. (e.g. canola, peanuts)

1. Process Selection: Thermal pressure or prepressure extraction is preferable. Thermal pressure uses high temperature to destroy cell structure and improve oil fluidity. Thermal pressure extraction combines heat pressure with solvent extraction to improve oil yield.

2. Operational Highlights:

• Thermal pressure requires high temperature steam (120-150°C) to degenerate proteins, destroy cell structures and promote oil precipitation.

In the pre-pressing process, the remaining oil content in the pre-pressing cake must be kept below 15%, and the remaining oil is then extracted with n-hexane solvent.

3. For example, Peanuts can reach 60-70% at hot pressure and 30-40% at cold pressure. However, the aroma of cold pressed oil is stronger.

Low-Oil Content Oilseeds (e.g. (e.g. soybean, rice bran)

1. Process selection: direct extraction as the main, extruder as the auxiliary. The extraction method can reduce residual oil yield to less than 1% by solvent spraying and soaking.

2. Operational Highlights:

extraction method uses n-hexane solvent and multiple spraying and immersion steps to extract the oil thoroughly.

• Crushing requires a combination of softening and steaming, but yields less oil than extraction method. It applies to small-scale production or specialized petroleum product needs.

 

Hard Oilseeds (e.g. soybean, cottonseed)

1.Adjustment Direction: strengthen the crushing and softening stage to meet the high pressure requirements of hard oilseeds.

2.Operational Highlights:

• Soybeans should be secondcrushed with particle size ≤0.5mm and softened at low temperature (50-60°C) to reduce elasticity and prevent failure due to insufficient plasticity during stripping.

Cotton seeds should be softened after removal, peeling thickness should be controlled between 0.3 and0.5mm, preventing the shell from not completely separating from the kernel, affecting oil yield.

3.Equipment Adaptation: A high torque oil press equipped with abrasionresistant drum is selected to meet the high pressure and friction of hard oilseeds.

Soft Oilseeds (e.g. canola, sesame seeds)

1.Adjustment Direction: Simplify pretreatment to minimize the risk of roller adhesion and maintain the aroma and nutrients of oils. Operational Highlights:

Rapeseed can be rolled directly (0.2-0.3mm thickness), but moisture content must be strictly controlled at ≤9% to prevent adhesion to the roller.

• Sesame seeds should be changed to water or pressed cold to avoid losing flavor and nutrients due to high temperatures.

Equipment Compatibility: Low friction roller to reduce soft oilseeds adhesion and temperature control system to ensure cool pressure ≤ 60 ℃.