The Question That Decides an Oil Mill's Profitability Before Machine Price
When an investor asks for a quotation on an edible oil production line from China, the first question is usually the price of the press. Yet the profitability of a vegetable oil plant is not set by equipment cost — it is set by how much oil stays trapped in the cake after pressing. A difference of two or three percentage points in residual oil means hundreds of tonnes of crude oil a year sold at feed prices instead of oil prices. Planning therefore has to start from three numbers: the seed type, its oil content and the daily seed throughput in tonnes.
Sections of a Complete Vegetable Oil Plant
A complete plant usually consists of four sections that can be purchased together or in phases:
- Preparation: seed cleaning, dehulling for sunflower and groundnut, cracking, conditioning and flaking.
- Pressing: screw presses for pre-pressing or full pressing, with filters to separate solids from the crude oil.
- Solvent extraction (optional): extractor, evaporators for hexane recovery and a desolventizer-toaster for the meal.
- Refining: degumming, neutralization, bleaching, deodorization, dewaxing where needed, then filling.
Oil Content by Seed and the Right Process for Each
| Seed | Approx. oil content | Recommended process |
|---|---|---|
| Soybean | 18 - 20% | Direct solvent extraction; pressing alone is not economical |
| Cottonseed | 18 - 22% | Pre-press then extraction, or pressing only at small capacities |
| Sunflower | 40 - 45% | Pre-press then extraction, or double pressing at small capacities |
| Canola / rapeseed | 40 - 44% | Pre-press then extraction |
| Groundnut | 45 - 50% | Hot or cold pressing depending on the target market |
| Sesame | 50 - 55% | Pressing, often cold pressing for premium oils |
The Formula for Real Oil Output
Never rely on an "oil yield" figure from a supplier without knowing how it was calculated. Use this simple formula (ignoring moisture for simplicity): cake mass = (seed mass × (1 − seed oil content)) ÷ (1 − residual oil in cake); then extracted oil = oil in seed − oil left in cake.
Worked example: a plant processing 50 tonnes of sunflower seed per day at 42% oil content. The seed contains 21 tonnes of oil and 29 tonnes of other material. With pressing alone, residual oil in the cake is around 8%, giving 31.5 tonnes of cake that holds 2.5 tonnes of oil — so extracted oil is about 18.5 tonnes per day. With pre-pressing followed by solvent extraction, residual oil drops to around 1% and extracted oil rises to about 20.7 tonnes per day. The gap is 2.2 tonnes a day, or roughly 670 tonnes of crude oil over 300 operating days a year. Multiply that by the crude oil price in your market to see the true value of the technology decision.
Mechanical Pressing or Solvent Extraction?
| Criterion | Mechanical pressing | Pre-press + solvent extraction |
|---|---|---|
| Residual oil in cake | 6 - 10% | Below 1% |
| Economical capacity | From 1 to about 100 t/day | Typically from 50 - 100 t/day upward |
| Investment and site requirements | Low, no explosion-proof zones | High, requires an explosion-proof zone, safety distances and special permits |
| Main consumables | Mainly electricity | Electricity, steam and hexane, usually quoted at 1 to 3 kg per tonne of seed |
| By-product | Oil-rich cake for animal feed | Low-fat, high-protein meal |
| Best suited for | Small and medium projects and premium oils | Large capacities and low-oil seeds |
The golden rule: every percentage point of residual oil in the cake is a permanent loss repeated on every operating day. Write a guaranteed, lab-measurable residual oil figure into the contract for the trial run — not just the press capacity in tonnes.
Sizing the Presses and Balancing the Line
Chinese screw presses are rated by seed throughput in tonnes per day, but that figure varies widely with seed type, degree of dehulling and pressing method. The same press can handle two to three times more seed in pre-pressing than in full pressing, because pre-pressing leaves roughly 15 to 20% oil in the cake for the extractor to recover. Ask the supplier for guaranteed capacity on your specific seed and your chosen pressing method. Size the preparation section about 10 to 15% above press capacity, because feed interruptions or fluctuating seed moisture raise residual oil and accelerate wear on press shafts and cage bars.
Why Conditioning and Seed Moisture Matter
Pressing efficiency is created before the press. Seeds normally need heat and moisture conditioning in a cooker before pressing, and drifting away from the optimum moisture produces either a soft cake that releases oil slowly or an over-dried cake that overloads the press and darkens the oil. Ask the supplier for the recommended temperature and moisture table for each seed, and make sure the cooker carries real measuring instruments rather than relying on manual estimation.
The Refinery: Batch or Continuous?
In most markets crude oil is not sold directly to consumers; it passes through refining stages that remove gums, free fatty acids, pigments and odours. Batch refineries suit small capacities up to about 20 tonnes of oil per day and give flexibility when switching oil types, while continuous refining becomes more economical above 30 tonnes per day thanks to lower losses and energy use per tonne.
- Chemical refining suits low-FFA oils such as sunflower and soybean and relies on caustic soda neutralization.
- Physical refining suits high-FFA oils such as palm oil; free fatty acids are distilled off during deodorization, which reduces losses.
- Deodorization typically runs at 230 to 260 °C under high vacuum, so ask about the vacuum system, heat source and thermal oil heater capacity.
- Sunflower oil needs a dewaxing (winterization) stage so it does not turn cloudy in the bottle at low temperatures.
Total refining loss typically ranges from 2 to 5% depending on the free fatty acid and gum content of the crude oil, and it must be built into the feasibility study before sizing the refinery and filling line.
Common Mistakes When Importing an Oil Plant from China
- Buying a press designed for one seed and running another seed without changing the cage bar and worm shaft configuration.
- Contracting on "press capacity" without specifying residual oil in the cake and solids content in the crude oil.
- Adding a solvent extraction unit without an explosion-proof zone, safety distances and a compliant fire suppression system.
- Skipping the dehulling section for sunflower, which raises fibre in the cake, lowers its feed value and wears out the presses quickly.
- Failing to require stainless steel on parts in contact with refined oil, especially the deodorizer.
- Ignoring CE marking and food-grade equipment conformity, which later stalls customs clearance and health licensing.
What to Demand Explicitly in the Quotation
- Throughput in t/day for your specific seed, and guaranteed residual oil in the press cake or extracted meal.
- Electricity consumption in kWh, steam in kg and hexane in kg per tonne of seed.
- Expected refining loss per stage, and refined oil specifications for acidity, colour and peroxide value.
- A site layout with elevations, since extraction and refining sections often require multi-storey buildings.
- A wear-parts list — press worm shafts, cage bars and filter cloths — for one full year of operation.
- Trial-run terms using a sample of your own seed, with results measured by an independent laboratory.
A successful oil plant is designed around the seed and the extraction rate, not the price of the press. If you are planning an edible oil pressing or refining plant or expanding an existing line, contact our team for an accurate oil yield calculation and technical specifications matched to your seed before you release any down payment.