Seed oil is made by cleaning and preparing seeds, then extracting the oil through mechanical pressing, chemical solvents, or a combination of both. The finished product you buy at a grocery store has typically gone through additional refining steps to remove impurities, color, and odor. The process ranges from surprisingly simple (a single press) to highly industrial (chemical washes, high heat, and multiple purification stages), depending on the scale and the type of oil being produced.
Cleaning and Preparing the Seeds
Every seed oil starts the same way: with raw seeds that need to be cleaned. Harvested seeds arrive with soil, plant debris, and stray seeds mixed in, all of which get removed in the first step. For some seeds, the outer hull is also stripped away at this stage to improve the quality of the final oil.
Once clean, larger seeds are crushed or broken into smaller, uniform pieces. These pieces are then conditioned with heat to soften the seed material and make the oil easier to extract. Think of it like warming butter so it spreads more easily. This conditioning step is what separates standard pressed oils from cold-pressed ones, which skip or minimize the added heat.
Mechanical Pressing: Cold Press vs. Expeller
The most straightforward way to get oil out of a seed is to squeeze it. A screw press (also called an expeller) feeds seeds through a barrel with a rotating screw that generates enormous pressure. No external chemicals are needed. The oil flows out one side, and the solid leftover material, called press cake, comes out the other.
The key difference between cold-pressed and expeller-pressed oil is temperature. Cold pressing keeps the seed material below about 122°F (50°C), preserving more of the oil’s natural flavor, color, and nutrients. Expeller pressing generates significantly more friction, pushing temperatures to 140–210°F (60–99°C). That extra heat helps squeeze out more oil per batch, but it also begins to break down some heat-sensitive compounds.
Mechanical pressing alone typically yields 35% to 45% of the seed’s total oil content with a high-quality industrial screw press. That means a good portion of oil remains trapped in the leftover cake, which is why many large producers follow up with solvent extraction.
Solvent Extraction With Hexane
Most commercially produced seed oils use a chemical solvent, almost always hexane, to pull out the remaining oil that pressing leaves behind. The process works because hexane dissolves oil but not the other seed components, so it acts like a selective rinse.
Seeds are first processed into flakes, cracked pieces, or pre-pressed cake to expose as much surface area as possible. These are then washed with hexane, which absorbs the oil. The hexane-oil mixture is then heated to 63–69°C (145–156°F), the boiling range of hexane, which causes the solvent to evaporate off. The evaporated hexane is captured through distillation and recycled for the next batch.
The result is crude oil that still contains traces of hexane. European Union regulations cap hexane residue in finished edible oils at 1 mg per kilogram. Testing in Malaysia found that some sunflower oils exceeded this limit, which highlights why the refining steps that follow matter.
Refining: How Crude Oil Becomes Shelf-Stable
Crude seed oil, whether from pressing or solvent extraction, is cloudy, strongly flavored, and spoils relatively quickly. The refining process, often abbreviated as RBD (refined, bleached, deodorized), transforms it into the clear, neutral oil you recognize on store shelves.
Refining involves several stages. First, free fatty acids and other impurities are neutralized, either with an alkaline wash (chemical refining) or through steam distillation at high temperatures (physical refining). Next comes bleaching, which despite the name has nothing to do with household bleach. The oil is passed through bleaching earth or activated carbon, materials that absorb pigments, residual soaps, and trace metals. This is what gives refined oil its pale, uniform color.
After bleaching, some oils go through winterization (also called dewaxing). The oil is heated to about 55°C (131°F) to fully liquefy it, then slowly cooled to 10–15°C (50–59°F) and held at that temperature for several hours. Waxes and saturated fats solidify and are filtered out, which keeps the oil from turning cloudy in your refrigerator.
The final step is deodorizing, where the oil is exposed to high-temperature steam under vacuum. This strips out volatile compounds responsible for strong or off-putting smells. The goal of the entire RBD process is a lighter color, neutral odor, longer shelf life, and the removal of any contaminants picked up during extraction.
What Refining Does to Nutrients
The trade-off for a clean, stable oil is nutrient loss. Vitamin E (present in seeds as compounds called tocopherols and tocotrienols) is particularly vulnerable to heat. When seed oil blends were heated to 170°C (338°F), the most common form of vitamin E was completely destroyed in most samples. At 200°C (392°F), total vitamin E content dropped to just 1–6% of the original amount in unheated oil.
Polyphenols and carotenoids, which act as natural antioxidants, also diminish during refining. These compounds normally help protect the oil’s polyunsaturated fatty acids (the omega-6 and omega-3 fats) from breaking down. As they’re stripped away, the oil becomes more susceptible to oxidation over time, even though it appears more stable on the shelf thanks to the removal of other reactive compounds. The omega fatty acids themselves do degrade with heat, and the higher the temperature, the greater the breakdown.
This is the core reason cold-pressed oils command higher prices. By avoiding high heat and chemical processing, they retain far more of their original vitamins, antioxidants, and flavor. The compromise is a shorter shelf life and stronger taste that doesn’t suit every cooking application.
How Much Oil Seeds Actually Contain
Not all seeds are equally oil-rich. Sunflower seeds yield roughly 41 grams of oil per 100 grams of seed, making them one of the more productive oilseeds. Rapeseed (the source of canola oil) yields about 39 grams per 100 grams. Soybeans are considerably leaner, which is why soybean oil almost always requires solvent extraction to be commercially viable.
In practice, no extraction method captures 100% of the available oil. Mechanical pressing leaves behind a press cake that still contains anywhere from 1% to over 20% residual oil, depending on the seed type and equipment. Solvent extraction pushes that residual number much lower, which is why the two methods are often used in sequence: pressing first to capture the bulk, then hexane to mop up the rest.
What Happens to the Leftover Cake
The solid material left after oil extraction retains roughly 40–50% of the seed’s original protein, fiber, minerals, and bioactive compounds. Far from waste, this press cake is a valuable byproduct. Soybean cake can contain up to 52% protein, and flaxseed cake can reach 56% protein and 66% fiber.
The most common use is animal feed, where the high protein content makes it a staple ingredient. Increasingly, though, food manufacturers are incorporating oilseed cakes into human products: gluten-free breads, protein-enriched cookies, and plant-based meat alternatives like vegan burgers. Compressed dietary supplements made from sunflower, coconut, pumpkin, and flaxseed cakes are also sold for direct consumption. Non-edible cakes end up as organic fertilizer or feedstock for biogas production.
Making Seed Oil at Home
Home oil presses do exist, and they work on the same screw-press principle as industrial expellers, just at a fraction of the scale. These are compact, countertop-sized machines designed for small, occasional batches. You feed in raw seeds (sunflower, flax, sesame, rapeseed) and collect the oil that drips out.
Expect significantly lower yields than a commercial operation. Home presses lack the pressure and conditioning steps that maximize extraction, so you’ll use a lot of seeds for a relatively small amount of oil. The oil you get, however, is genuinely fresh and unrefined, with all its natural flavor, color, and nutrients intact. It’s essentially the cold-pressed equivalent of what you’d pay a premium for at a specialty store. Just keep it refrigerated and use it within a few weeks, since it won’t have the shelf stability of refined oil.
For anyone not ready to invest in a press, even a high-powered blender and a fine mesh strainer can produce small quantities of oil from high-fat seeds like sunflower or sesame, though the yield will be minimal and the process messy. A dedicated hand-crank or electric oil press, available for roughly $100–$300, is a far more practical option if you plan to do this regularly.