Pre-Pressing
What pre-pressing is
Pre-pressing is the answer to a specific problem: what to do with high-oil seeds in a large, solvent-based plant. Seeds like sunflower, rapeseed/canola and groundnut contain a lot of oil — often 40–50% — and feeding that much oil straight into a solvent extractor overloads it: the flakes are too oil-rich to handle well and the miscella becomes too concentrated. So the plant first runs the prepared seed through a screw press, but only partially. Rather than chasing maximum yield, the press is set to remove roughly half to two-thirds of the oil, producing a pre-press cake that still holds around 15–20% oil. That cake — now at an oil level the extractor is designed for — goes on to solvent extraction, while the mechanically expressed oil is collected separately.
Why high-oil seeds are pre-pressed
Pre-pressing exists because the two ‘pure’ routes both fall short for high-oil seed. Full pressing alone (running the expeller hard) leaves 6–12% of the oil in the cake — a large loss on a high-value, high-oil crop — and strains the machine. Direct solvent extraction alone struggles because very oil-rich flakes extract and drain poorly and swamp the solvent system. Pre-press plus solvent combines the strengths of both: the press cheaply and quickly removes the bulk of the oil mechanically (no solvent needed for that fraction), and the solvent step then mops up the remaining oil down to about 1% in the meal. The result is high overall recovery at reasonable cost, which is why the pre-press/solvent combination is the standard design for high-oil seeds, while low-oil soybean is usually flaked and sent straight to solvent without pre-pressing at all.
How pre-pressing differs from full pressing
Mechanically, a pre-press and a full press are the same kind of machine — a screw press — run to a different target. In full pressing, the operator tightens the choke and runs hard to extract as much oil as the machine can, accepting lower throughput and higher wear for maximum mechanical yield. In pre-pressing, the press is run more gently and at higher throughput, deliberately leaving 15–20% oil in the cake because a solvent step will finish the job far more completely than pressing ever could. This makes pre-pressing easier on the machine and faster per tonne, and it means the pre-press cake is designed as a feed for extraction, not a finished product. The distinction is entirely about intent and setting, which is why the same screw press can serve either role.
Pre-press oil and the two oil streams
One practical consequence of pre-pressing is that a plant ends up with two oil streams: the mechanically pressed oil from the pre-press, and the solvent-extracted oil recovered from the cake. The pressed fraction is a straightforward mechanical oil, while the extraction oil is recovered from miscella after the solvent is stripped off. Plants may handle these separately or combine them before refining, but both ultimately go through refining to become finished edible oil, so the split matters more for processing than for the final product. What it does underline is that pre-pressing is a front-end step in an integrated plant, not a standalone method — its whole purpose is to feed the extractor and refinery efficiently, which is why it only makes sense at the scale where solvent extraction and refining are already in place.
Where pre-pressing fits
Pre-pressing is a large-plant, high-oil-seed technique, and understanding it clarifies the whole extraction map. Small mills without a solvent plant do the opposite — they full-press and sell the cake as feed. Big plants processing low-oil soybean skip pressing and go direct to solvent. Big plants processing high-oil sunflower, rapeseed or groundnut sit in between: they pre-press then extract. So the three configurations — full-press-only, pre-press-plus-solvent, and direct-solvent — map neatly onto seed oil content and plant scale, and pre-pressing is the bridge that makes solvent extraction efficient for the oil-rich crops. For the step that follows, see solvent extraction; for how the two routes compare head-to-head, see expeller vs solvent extraction.
Key figures (indicative)
| Parameter | Typical |
|---|---|
| What it is | partial screw pressing before solvent extraction |
| Cake residual | ~15–20% oil (designed feed for extraction) |
| Used on | high-oil seeds — sunflower, rapeseed/canola, groundnut |
| Not used on | low-oil soybean (flaked straight to solvent) |
| Paired with | solvent extraction (finishes to ~1% oil in meal) |
| Vs full press | run gentler, higher throughput, less wear |
FAQ
What is pre-pressing in oil extraction?
A partial screw-press step used on high-oil seeds in solvent plants: the expeller is run gently to remove only part of the oil, leaving a cake with about 15–20% residual oil that then goes to solvent extraction to recover the rest.
Why are high-oil seeds pre-pressed instead of full-pressed?
Full pressing leaves 6–12% of the oil in the cake — a large loss on an oil-rich crop — while feeding very oil-rich flakes straight to solvent overloads the extractor. Pre-pressing removes the bulk of the oil cheaply, then solvent recovers the rest, giving high overall yield at reasonable cost.
What is the residual oil in pre-press cake?
Indicatively around 15–20%, deliberately higher than a full-press cake because a solvent step follows to bring the meal down to about 1% oil. Actual figures vary with seed, preparation and how the press is set.
Which seeds are pre-pressed and which go straight to solvent?
High-oil seeds — sunflower, rapeseed/canola, groundnut — are usually pre-pressed then extracted; low-oil soybean is usually flaked and sent straight to solvent extraction without pre-pressing.