Seed oil extraction is the process of collecting oil from many oil‑bearing materials. These include soybeans, canola or rapeseed, sunflower seeds, peanuts, and specialty materials like macadamia nuts, walnuts, and almonds. In seed oil extraction, some processors rely on the mechanical method using a screw press or expeller. Others prefer solvent extraction or specialized equipment. Each processing method has its own advantages and disadvantages. In this blog post, we’ll explore some of the most common extraction methods and the benefits and drawbacks of each.
Screw Press/Expeller Mechanical Oil Extraction
Mechanical seed oil extraction remains one of the oldest and simplest methods for separating oil from oil‑bearing materials. This method involves pressing the materials seeds using a screw press to extract the oil. Operators often crack or flake the seeds and condition them to the correct moisture and temperature. Then, they use a screw press to extract the oil. The oil is then filtered and frequently refined before usage. This extraction method produces high-quality oil that manufacturers commonly use for food applications. The solids (press cake) is often used for animal feed.
A key advantage of mechanical extraction is that it doesn’t require solvents or chemicals. This makes the process simple, safe, and efficient. Solvent-free full press extraction is an environmentally friendly method of oilseed extraction, as it does not produce any hazardous waste. Mechanical extraction is more economical for small‑capacity operations under 500 tons per day. However, it’s not always suitable for every type of oil‑bearing material. Also, the amount of oil that is recovered is higher than using the solvent extraction method with residual oil in the press cake typically in the range of 4.0% to 8.0% depending on the material being processed.
Cold Pressing Extraction
On some oil bearing materials the heat used in the mechanical extraction process can cause some degradation of the oil and press cake. For these materials the mechanical extraction process is used but at lower temperatures. Producers can process the material with a screw press, expeller, or hydraulic press. Our screw presses are unique in that the press shaft and the surrounding cages can be water cooled to further assist in keeping the operating temperatures as low as possible. Cold pressing yields oil that maintains high quality, rich nutrients, and a distinctive aroma.
One of the other main advantages of cold pressing is that it produces high-quality oil without the use of solvents or chemicals. Due to the high quality oil and the heath advantages, cold pressing is gaining popularity in the consumer market in comparison to refined/solvent based-oils. However, cold pressing can be slower and less efficient than other extraction methods, and it may not be suitable for all types of oilseeds.
Solvent Extraction
Solvent seed oil extraction is another widely used method that employs petroleum‑based solvents such as hexane to separate the oil from oilseeds. The seeds are first ground flaked and conditioned, and then the solvent is added to the material in the solvent extractor. The solvent separates dissolves the oil from the solids. The oil exits the extractor with the solvent, which is then separated from the solvent using a distillation process. The solids also have to be desolventized in a separate desolventizer-toaster (DT).
Solvent extraction is generally considered to be a more efficient method of extraction than mechanical pressing for larger capacity processes above 500 tons per 24 hour day, and it can be used to extract oil from a wide variety of oilseeds. This process can typically reduce the oil content in the solids to less than 2.0% and on some materials down to 1.0% or less. However, the use of solvents can be a safety concern, and it can also affect the quality of the resulting oil as the oil is exposed to high temperatures in the final stage to evaporate out the hexane and minute amounts of solvent can remain. Legislators in the European Union are raising concern over the use of hexane, derived from petroleum, for the extraction of oils and vegetable proteins. Other areas of the world will likely follow.
Supercritical CO2 Extraction
Supercritical CO₂ seed oil extraction is a relatively new process that uses carbon dioxide, liquefied under high pressure, as a clean and efficient solvent. The seeds are first ground into a fine powder. Then they are exposed to supercritical CO2, which separates the oil from the solids. The resulting oil is then separated from the CO2. This process is typically used for specialty, high value products and operates at much lower capacities than solvent extraction.
Supercritical CO2 extraction of oilseeds is generally considered to be a safe and efficient method of extraction that produces high-quality oil. However, it requires specialized equipment, which can be expensive, and it may not be suitable for all types of oilseeds.
Consider a Mechanical Screw Press from French
Oilseed extraction is a complex process that involves a variety of factors. You must consider the type of oilseed, the desired quality of the oil, and the equipment available. At French Oil Mill Machinery Company, we offer the best oilseed equipment. Browse our equipment designs and request a quote today.