Most cooking oils start as seeds, nuts, or fruits and go through a combination of mechanical pressing, chemical extraction, and refining before reaching your kitchen. The exact process depends on the source material and the type of oil being produced, but nearly all follow the same general path: prepare the raw material, separate the oil from everything else, then clean it up for sale.
Preparing Seeds Before Extraction
Before any oil can be squeezed or pulled from a seed, the raw material needs to be cleaned and broken down. Most oilseeds go through cleaning, drying, dehulling, size reduction, flaking, and conditioning. The cleaning step, sometimes called scalping, uses rotating screens and airflow to remove stems, leaves, sticks, and other debris that could spoil the batch during storage or processing.
After cleaning, seeds are typically cracked open and their hulls removed, then rolled into thin flakes. Flaking dramatically increases the surface area, which makes it easier for oil to escape the cells during the next stage. Many operations also heat and condition the flakes to soften the cell walls and help the oil flow more freely.
Mechanical Pressing
The oldest and simplest way to extract oil is to crush the raw material under pressure. Modern operations use a screw press, sometimes called an expeller, which works like a giant drill bit inside a barrel. Seeds are fed in one end, and the rotating screw forces them forward under increasing pressure, squeezing oil out through small gaps in the barrel while pushing the leftover meal out the other side.
Friction from this process generates heat naturally. In conventional expeller pressing, seeds are often cooked or steamed beforehand to soften them and release more oil. Cold pressing skips that step entirely. Raw, uncooked seeds go straight into the press, which means the machine has to apply significantly more torque to extract oil through pressure alone. The trade-off is lower yield but a less processed product that retains more of its original flavor and nutrients.
For extra virgin olive oil, the process looks different because olives are a fruit, not a seed. Olives are crushed into a paste, then slowly mixed in a trough with spiral blades (a step called malaxation) for 20 to 45 minutes while keeping the temperature below 27°C (about 81°F). The paste then goes into a centrifuge that spins at high speed to separate the oil from the skins, pits, and water. A second centrifuge spin may follow to remove any remaining water.
Solvent Extraction
Mechanical pressing can only recover so much oil. For large-scale production, especially from lower-oil seeds like soybeans, the industry uses solvent extraction to pull out nearly everything that’s left. The prepared seed flakes are washed with a petroleum-based solvent, typically hexane, which dissolves the oil out of the solid material and creates a mixture of oil and solvent called miscella.
From there, the process splits into two recovery tracks. The oil-solvent mixture goes through distillation columns where heat evaporates the hexane away from the oil. A final stripping column, heated indirectly with steam, removes any lingering solvent and moisture. Meanwhile, the spent seed meal also contains residual solvent, which is removed in a separate unit that heats and toasts the meal. All the recovered hexane vapor is condensed and recycled back into the extractor for reuse.
The FDA requires that residual hexane in finished edible oils fall below detectable levels, with a limit of quantitation set at 1 milligram per kilogram. In practice, the distillation process is thorough enough that commercial refined oils contain virtually no solvent residue.
Refining, Bleaching, and Deodorizing
Crude oil straight from the press or solvent extractor isn’t what you see on store shelves. It contains phospholipids, free fatty acids, pigments, and volatile compounds that affect taste, color, shelf life, and cooking performance. Turning crude oil into the clear, neutral product most people buy requires three main steps, known in the industry as RBD: refining, bleaching, and deodorizing.
Refining starts with degumming, which removes phospholipids. The simplest version mixes water into the oil, which causes certain phospholipids to clump together so they can be spun out by centrifuge. More stubborn phospholipids require acid treatment. In soybean oil production, these removed phospholipids (called gums) are a source of lecithin, a common food additive you’ll see on ingredient labels for everything from chocolate to salad dressing. After degumming, free fatty acids are neutralized, often with a caustic solution that converts them into soap, which is then separated out.
Bleaching comes next. Despite the name, it doesn’t use chlorine or household bleach. Instead, the oil is mixed with a special type of clay that adsorbs pigments and compounds that would otherwise accelerate spoilage. This is what gives refined oils their pale, uniform color compared to the deeper tones of unrefined versions.
Deodorizing is the final step. The oil is heated under vacuum, which strips away volatile compounds responsible for strong or off-putting flavors. What’s left is a mild, shelf-stable oil ready for bottling.
How Refining Changes the Oil
The most noticeable practical difference between refined and unrefined oils is their smoke point, the temperature at which an oil starts to break down and produce visible smoke. Refining removes the free fatty acids and impurities that cause oil to smoke at lower temperatures, which is why refined oils can handle much higher heat.
The differences can be dramatic. Refined peanut oil has a smoke point around 232°C (450°F), while unrefined peanut oil smokes at just 160°C (320°F). Refined safflower oil can reach 266°C (510°F) compared to only 107°C (225°F) for unrefined. Refined avocado oil handles 271°C (520°F), while virgin avocado oil tops out around 200°C (392°F). Refined coconut oil smokes at about 204°C (400°F) versus 177°C (350°F) for virgin.
The flip side is that unrefined oils keep more of their original flavor, aroma, and minor nutrients like polyphenols and vitamin E. That’s why cold-pressed or virgin oils tend to taste more like their source material and work better in dressings, dips, or low-heat cooking where you want that flavor to come through.
How Essential Oils Are Made
Essential oils are a completely different product from cooking oils. They’re concentrated aromatic compounds extracted from flowers, leaves, bark, or roots, and they’re produced using different methods.
Steam distillation is the most common technique. Plant material is placed in a chamber, and steam passes through it, carrying volatile aromatic compounds with it. The steam then cools in a condenser, turning back into liquid. Since the essential oil doesn’t mix with water, it floats on top and is skimmed off. This method is widely used because water is inexpensive and environmentally friendly, but the high temperatures can damage delicate compounds in some plants.
For more fragile botanicals, producers sometimes use solvent extraction with hexane or other organic solvents, which works at lower temperatures and captures a broader range of aromatic compounds. The downside is that evaporating and recovering the solvent is time-consuming and can introduce trace impurities. Citrus essential oils, by contrast, are typically cold pressed directly from the fruit peel, similar in concept to how olive oil is made. Traditional methods like enfleurage, where flowers are pressed into animal fat that absorbs their fragrance, are largely historical curiosities today, replaced by more efficient industrial techniques.