Soybean oil is primarily extracted through mechanical pressing or solvent extraction methods.
Harvesting soybean oil involves extracting the oil from the soybeans themselves. This is not like harvesting a liquid crop, but rather processing the solid soybean seeds to separate the oil component. The main techniques used are mechanical pressing and solvent extraction.
Mechanical Pressing Explained
Mechanical pressing is a physical method of extracting oil from soybeans. This process involves applying pressure to the beans to force the oil out.
- The Process: Soybeans are typically cleaned and then crushed using mechanical presses. These presses can be screw presses or expeller presses. The action of the screw or press applies significant pressure, squeezing the oil from the bean material.
- Types Produced: Mechanical pressing yields oil varieties known as cold-pressed or expeller-pressed oil.
- Characteristics: Oils produced this way often retain more of the soybean's natural flavor compared to solvent-extracted oils. The yield of oil from mechanical pressing alone is generally lower than with solvent extraction.
Solvent Extraction Process
Solvent extraction is a chemical method widely used for extracting soybean oil due to its efficiency in maximizing oil yield.
- The Process: This method uses a solvent, commonly hexane, to dissolve the oil out of prepared soybean flakes. The soybeans are first cleaned, cracked, dehulled, and rolled into thin flakes to increase the surface area. The solvent is then passed through these flakes, dissolving the oil.
- Separation: After the oil is dissolved in the solvent, the resulting mixture (called miscella) is separated from the solid soybean material (defatted flakes). The solvent is then evaporated from the miscella, leaving behind the crude soybean oil. The solvent is recovered and reused.
- Efficiency: Solvent extraction is highly efficient and extracts most of the oil contained within the soybeans.
Comparing Extraction Methods
While both methods effectively extract oil, they differ in process, yield, and the characteristics of the resulting oil.
| Feature | Mechanical Pressing | Solvent Extraction |
|---|---|---|
| Method | Physical (Crushing/Squeezing) | Chemical (Dissolving using solvent) |
| Primary Output | Cold-Pressed, Expeller-Pressed Oil | Crude Soybean Oil (requires refining) |
| Solvent Used | None | Yes (e.g., Hexane) |
| Oil Yield | Lower | Higher (more efficient) |
| Flavor | More distinct, can vary with process heat | Neutral (after refining) |
Often, a combination of both methods is used, where soybeans are first expeller-pressed, and the remaining oil in the press cake is then extracted using a solvent to maximize yield.
