Soybean oil is produced by extracting fat from soybeans using either chemical solvents or mechanical pressing, then refining the crude oil to remove impurities. Soybeans contain about 20% oil by weight, and the process of getting that oil out involves careful seed preparation, extraction, and several purification steps. Here’s how it works at both industrial and small scales.
Seed Preparation
Before any oil can be extracted, soybeans need to be cleaned, conditioned, and physically broken down to make the oil accessible. At industrial facilities, this means removing dirt, stones, and damaged beans, then adjusting the moisture and temperature of the seeds. The ideal moisture content for processing sits between 8% and 12%, with 10% being the sweet spot. Moving too far outside that range, below about 7% or above 13%, noticeably reduces the amount of oil you can recover.
Once conditioned, the beans are cracked into smaller pieces, dehulled to remove the outer skin, and then rolled into thin flakes. Flaking is the critical step here. Thin flakes expose far more surface area than whole beans, which lets the solvent or press reach the oil trapped inside the cells. These prepared flakes are what enter the extraction stage.
Industrial Solvent Extraction
The vast majority of commercial soybean oil is made using solvent extraction, a process that washes the prepared flakes with a petroleum-based solvent (typically hexane) to dissolve and carry away the oil. The flakes move through an extractor where the solvent repeatedly contacts them, pulling out nearly all the available fat. Modern solvent extraction recovers 97% to 99% of the oil in the bean, leaving behind a meal with only 0.5% to 1.2% residual oil.
After extraction, the solvent-oil mixture is heated to evaporate the hexane, which is then captured and recycled. The resulting crude soybean oil still contains phospholipids, free fatty acids, pigments, and trace impurities that need to be removed before it’s suitable for cooking or food manufacturing.
Regulations limit hexane residue in finished oil to no more than 1 mg/kg in the European Union. By the time crude oil goes through refining, virtually all solvent traces are gone.
Mechanical Pressing
Mechanical pressing, sometimes called expeller pressing, uses physical pressure to squeeze oil out of the beans rather than dissolving it with chemicals. This method is simpler and doesn’t involve solvents, which is why it appeals to people making oil at home or producers marketing “cold-pressed” or “chemical-free” products.
The trade-off is efficiency. A single mechanical press recovers roughly 85% to 92% of the available oil, and even with optimized preparation you’ll top out around 93% to 95%. The leftover meal retains 5% to 8% oil compared to about 1% from solvent extraction. For a home press, expect around 90 grams of oil from 500 grams of soybeans, or roughly an 18% yield. The process itself is straightforward: feed dried soybeans into the press, and oil and pressed cake come out separately. A small batch takes under an hour.
Home oil press machines designed for soybeans are widely available and work by feeding beans through a screw mechanism that generates pressure and friction. No chemicals are involved, and the resulting oil is unrefined, retaining more of the bean’s natural flavor and color.
Refining Crude Soybean Oil
Crude soybean oil, whether solvent-extracted or pressed, goes through several refining steps before it becomes the clear, neutral oil you find on store shelves. Each step targets a different category of impurity.
Degumming
The first step removes phospholipids, naturally occurring compounds that make crude oil cloudy and unstable. Some of these dissolve easily in water and can be washed out simply by mixing the oil with hot water and separating the layers. Others resist water and require an acid treatment or enzyme treatment to convert them into a form that can be removed. Enzymatic degumming is a newer technique that uses specialized enzymes to break apart these stubborn phospholipids.
Neutralization
Free fatty acids give crude oil an unpleasant taste and accelerate spoilage. In chemical refining, an alkaline solution (sodium hydroxide) is mixed into the oil to neutralize these acids, forming soaps that are then spun out in a centrifuge. In physical refining, the free fatty acids are instead removed later during deodorization by heating the oil under vacuum, which causes them to evaporate while the oil itself stays behind.
Bleaching and Deodorizing
Bleaching passes the oil through absorbent clays that pull out pigments, residual soaps, and trace metals. This lightens the color and improves stability. Deodorizing is the final step: the oil is heated to high temperatures under vacuum, which strips out volatile compounds responsible for off-flavors and odors. The result is a clean, pale, neutral-tasting oil with a smoke point of about 234°C (453°F), making it well suited for frying, baking, and general cooking.
What’s Left Behind: Soybean Meal
Oil extraction produces far more meal than oil. Since soybeans are only about 20% fat, the remaining 80% becomes soybean meal, a protein-rich byproduct containing roughly 47% to 49% protein. This meal is one of the most important animal feed ingredients in the world, used extensively in poultry, swine, and aquaculture diets. It also serves as feedstock for organic fertilizers, dietary supplements, and bio-based products, though its use in human food is still limited compared to its role in animal nutrition.
Nutritional Profile of Soybean Oil
Soybean oil is predominantly polyunsaturated fat. Its main fatty acid is linoleic acid (an omega-6 fat) at about 51 to 53%, followed by oleic acid (a monounsaturated fat) at around 22 to 24%. It also contains 7 to 8% alpha-linolenic acid, an omega-3 fat, which is relatively high for a common cooking oil. Saturated fats make up about 15 to 16% of the total, mostly from palmitic and stearic acids.
That high polyunsaturated content is a double-edged quality. It contributes to a favorable fat profile nutritionally, but it also makes soybean oil prone to oxidation. Rancidity develops faster in soybean oil than in oils with more saturated or monounsaturated fat.
Storage and Shelf Life
Because of its high polyunsaturated fat content, soybean oil is easily oxidized by heat, light, and air exposure. Store it in a cool, dry place away from direct sunlight, ideally in a dark or opaque container. Oil stored at room temperature maintains better quality over months than oil kept at elevated temperatures. Research on soybean oil-based products found that storage at 37°C (about 99°F) significantly increased peroxide values and acidity compared to room temperature storage, with quality declining steadily over six months.
Unrefined or cold-pressed soybean oil has a shorter shelf life than refined oil because it retains more of the natural compounds that accelerate oxidation. If you press your own oil at home, plan to use it within a few weeks and keep it refrigerated to slow rancidity.