Overview: the standard route for a high-oil seed
Rapeseed — and its food-grade variety canola — is a high-oil oilseed, typically carrying around 40–44% oil by weight. Because so much of each seed is oil, the economical and proven industrial route is pre-press followed by solvent extraction. A screw press first squeezes out the bulk of the oil; the remaining oil-bearing cake is then washed with hexane to recover almost all of what is left. This two-stage approach gives both high total yield and good throughput, which is why it is the default for high-oil seeds rather than full-pressing alone. Attempting to recover all of the oil by pressing alone would mean very high pressures, slow throughput, heavy wear on the press, and oil that is still left locked in the cake — so the industry splits the work between mechanical and solvent stages.
The other defining trait of rapeseed is its chemistry. Crude rapeseed oil is comparatively high in phospholipids (gums), so thorough degumming is essential before the oil can be refined into a stable, light product. The full production chain therefore runs from seed handling through mechanical pre-pressing, solvent extraction, and a complete refining sequence. The sections below follow that chain step by step. For a side-by-side look at the two oil-recovery methods, see pressing vs. solvent extraction.
The seed: rapeseed vs. canola
Rapeseed plants produce small, round, dark seeds with a hard hull and a high oil concentration. Historically, traditional rapeseed was naturally high in erucic acid and in glucosinolates, compounds that limited its use in food and feed. Canola is rapeseed that has been bred to be low in both — making the oil suitable for food use and the meal more valuable as animal feed. In practice the equipment and process for the two are essentially the same; the difference is the seed variety, not the machinery.
From a processing standpoint, the key facts are simple: the seed is small and high in oil, so it benefits from being flattened into thin flakes and conditioned with heat before oil recovery. Its naturally high phospholipid load means the crude oil will need careful gum removal downstream. These two characteristics — high oil content and high gum content — shape every step that follows, from how the flakes are cooked through how aggressively the crude oil must be degummed. Keeping these traits in mind makes the rest of the process easy to follow: each stage is essentially a response to one or the other.
Pretreatment: cleaning, conditioning, flaking, cooking
Before any oil is recovered, the seed is prepared so that the oil cells are opened up and the seed is in the right physical and thermal condition. This pretreatment stage has a direct effect on both yield and final oil quality.
Incoming seed is weighed, sampled, and cleaned to remove dust, stems, stones, metal, and other foreign matter. Magnets and screens protect downstream equipment and keep contaminants out of the oil.
The cleaned seed is gently warmed and moisture-adjusted so the hull and kernel soften. Properly conditioned seed flakes cleanly instead of shattering, which is critical for the next step.
Softened seed passes through flaking rolls that press it into thin flakes. Thin flakes have a short path for oil to travel out, which improves both pressing efficiency and later solvent penetration.
The flakes are heated and conditioned in a cooker. This ruptures remaining oil cells, lowers oil viscosity, and brings the flakes to the temperature and moisture that the press needs to work efficiently.
The detailed mechanics of this stage are covered in rapeseed pretreatment for oil and, more generally, in how oilseed pretreatment works.
| Pretreatment step | Purpose | Typical effect |
|---|---|---|
| Cleaning | Remove foreign matter | Protects equipment, cleaner oil |
| Conditioning | Soften seed | Clean flaking, less fines |
| Flaking | Thin the seed | Shorter oil path |
| Cooking | Rupture oil cells, heat flakes | Higher yield, better press feed |
Pre-pressing: the first oil recovery
With the flakes cooked and conditioned, the seed enters a screw press (expeller) for pre-pressing. The press squeezes the flakes under rising mechanical pressure, forcing out a large share of the oil. For a high-oil seed like rapeseed, the goal of pre-pressing is not to extract every drop — it is to remove the bulk of the oil and leave a cake that still holds roughly 16–20% residual oil, in a porous form ideal for solvent extraction.
This is the heart of why the route is called "pre-press." Trying to mechanically press a high-oil seed all the way down is slow and hard on the equipment, and it still leaves oil behind. By pressing only partway and finishing with solvent, the mill gets both high throughput and near-complete oil recovery. The oil released here is screened and clarified, then joins the extracted oil stream. For the machine itself, see how a screw oil press works and our oil press machines.
- Conditioned flakes feed into the press barrel.
- The rotating screw builds pressure along the barrel.
- Oil drains out through the cage slots and is collected.
- A firm cake exits the press at ~16–20% residual oil.
- Cake is broken up and sent to solvent extraction.
Video: a multi-stage screw oil press in our workshop.
Solvent extraction: recovering the rest
The pre-pressed cake still holds a meaningful amount of oil, and solvent extraction is what recovers it efficiently. The broken cake is washed with food-grade hexane, which dissolves the residual oil out of the cake. The resulting mixture of oil and solvent — called miscella — is separated, and the hexane is evaporated off and condensed for reuse, leaving crude rapeseed oil. The de-oiled flakes are stripped of residual solvent and become rapeseed meal.
This stage is what makes the overall process so efficient: it drives the residual oil in the spent material down to a very low level, far below what pressing alone could reach. Properly designed extraction, with full solvent recovery, is both economical and safe. The principles and equipment are explained in how solvent extraction works.
Refining: degumming is the critical first move
Crude rapeseed oil is dark, carries gums and free fatty acids, and is not yet suitable for the table. It is refined through the classic DBDW-style sequence — degum, neutralize, bleach, deodorize — to produce a clear, neutral, stable oil. For rapeseed, the degumming step is especially important because the crude oil is comparatively high in phospholipids; if the gums are not thoroughly removed, every downstream step suffers and the finished oil is unstable.
Water and/or acid is mixed with the warm oil to hydrate the phospholipids so they can be separated out. Thorough degumming is the foundation of good rapeseed oil and also yields lecithin. See how oil degumming works.
Free fatty acids are removed (commonly with alkali, or by physical refining), cutting acidity and improving stability.
The oil is treated with bleaching earth to adsorb color bodies, trace metals, and oxidation products, lightening the oil.
Steam under vacuum and heat strips out odor and flavor compounds, leaving the bland, neutral profile expected of canola oil.
The result is a light, neutral oil that is high in monounsaturated fats and low in saturated fats. Each refining step builds on the one before it: skipping or shortcutting degumming, for example, overloads the bleaching earth and leaves the deodorizer fighting problems that should have been removed earlier. Running the full sequence in order is what gives canola oil its characteristic clarity, bland flavor, and shelf stability. The full refining workflow is detailed in how to refine edible oil.
Yield & by-products
Because rapeseed is so oil-rich, total oil recovery across pre-press plus solvent extraction is high — the combined route captures the large majority of the seed's ~40–44% oil content. The two main co-products carry real value:
| Output | Source | Use |
|---|---|---|
| Refined rapeseed / canola oil | Press + extraction, refined | Edible oil |
| Rapeseed meal | De-oiled, desolventized flakes | Protein animal feed |
| Lecithin | Recovered during degumming | Food / industrial emulsifier |
Rapeseed meal is a protein-rich animal feed, and food-grade canola meal in particular is valued because the seed is low in glucosinolates, which improves its palatability and feeding value. Lecithin, separated during degumming, is a useful emulsifier in food and industrial applications. Because the meal typically represents a large share of the seed by weight, its quality and value matter to the overall economics of the plant, not just the oil. To estimate the oil, meal, and approximate outputs for a given seed throughput, our capacity calculator can help size the line and set realistic expectations.