Crush oilseed to a coarse meal and warm it to 120-160 degrees F (49-71 degrees C) before pressing, which raises the oil yield by 10-20%, but never above 160 degrees F, which degrades the oil and scorches the meal. Warming 100 kg of seed by 45 degrees C takes about 2.25 kWh of heat, and a lump of beeswax set on the meal, which softens at about 62 degrees C, tells you when to stop.
Part of Oil Pressing at Scale
Breaking seed open and warming it for pressing: crushing options, the temperature window, the heat needed, and what the expeller method means at village scale.
Crush Coarse, Not To Flour
Crushing ruptures the cells that hold the oil. The corpus advises a coarse, oily paste rather than a fine powder, because the solid fragments leave channels for oil to flow through under pressure (Oil Extraction). The carrier gives three tools: a mortar and pestle for small batches, a grain mill set coarse, and a wooden mallet on a stone slab. For a village’s thousands of kilograms use the mill, with the cautions in Powered Press about oily paste in the fine furrows of a grain mill.
The Temperature Window Is Narrow And The Corpus Gives Three Limits
The carrier says to warm the crushed seed to 120-160 degrees F, which is 49-71 degrees C (120 degrees F is (120 - 32) x 5/9 = 48.9 and 160 degrees F is (160 - 32) x 5/9 = 71.1), and not to exceed 160 degrees F, which degrades the oil and can scorch the meal. The wiki’s seed-pressing page says not above 60 degrees C (Seed Pressing), and the oil-extraction page describes light roasting for 10-15 minutes until the seed darkens slightly and smells nutty. These limits do not agree: 71 degrees C against 60. Where the oil is to be stored for months, take the lower limit of 60 degrees C and avoid roasting; roast only for flavour in oil that will be eaten soon (the idea that heat shortens keeping is a recalled general rule, not a corpus figure).
The Expeller Method At Village Scale
An expeller is a continuous screw press in which the turning screw crushes and presses the seed and its own friction heats it. A village-built press that works in batches replicates the same sequence by hand: crush, warm, press. The cool-pressed standard of keeping the meal at or below 49 degrees C (120 degrees F, the carrier’s lower bound) is a recalled convention; going to the upper end of the window raises yield at some cost in oil quality.
Heat Needed
Heat is mass x specific heat x temperature rise. Oilseed has a specific heat of about 1.8 kJ/kg-K (recalled). Warming 100 kg from 15 to 60 degrees C, a rise of 45 K, takes 100 x 1.8 x 45 = 8,100 kJ, which is 8,100 / 3,600 = 2.25 kWh. At an open pan efficiency of 10% (assumed) and 15 MJ/kg for dry wood (recalled) the fuel is 8.1 MJ / (15 MJ/kg x 0.10) = 5.4 kg of wood per 100 kg of seed. For a season of 4,158 kg of seed that is 4,158 x 2.25 / 100 = 94 kWh of heat and about 225 kg of wood.
What You Need
- A crusher: mortar, grain mill set wide, or a mallet on a slab
- A shallow pan and a low fire, or a water bath
- A lump of beeswax and a thermometer if you have one; beeswax softens at about 62 degrees C (recalled), a handy upper marker
- A stirring paddle and heat-proof cloths
Method: Crush And Warm
Step 1: Crush the seed coarse in batches you can warm and press while hot.
Step 2: Warm in a pan over low heat, stirring constantly. The wet method adds warm water, roughly 10-15% of the paste volume, and gentle heat (Oil Extraction).
Step 3: Watch the limit. Keep the meal where you can hold a hand over it comfortably; when the wax lump on the surface begins to soften, take it off the heat.
Step 4: Press immediately while warm, as the carrier says; cold meal gives less oil.
Step 5: Never walk away from the pan. Seconds make the difference between warm and scorched.
Worked Example: A Day’s Batch
A day’s pressing of 100 kg of seed starts at 15 degrees C. Warmed to 60 degrees C: heat 2.25 kWh. A pan of 20 kg warmed in each of five batches needs 0.45 kWh each. The extra yield: the carrier’s 10-20% on a 60% base recovery moves it to 66-72%, which is 40 x 0.66 = 26.4 up to 40 x 0.72 = 28.8 kg of oil from 100 kg of 40% seed instead of 24 kg.
Common Mistakes
- Overheating to chase yield. Above 160 degrees F the oil degrades and the meal scorches.
- Letting the meal cool before pressing. Press while warm.
- Grinding to flour. It blocks the channels the oil needs.
Hot meal, hot oil and fire
Hot oily meal burns skin badly and oil in a pan can catch fire. Use a low fire, keep the pan away from sparks, never leave it, and smother an oil fire with a lid or dry sand; water thrown on burning oil spreads it (Lamp Fire Prevention). Seed dust is combustible: keep open flame away from the crushing area and never test for dust with a flame.
What’s Next
- Learn next: Pressing and Extraction - the press stage
- Combine with: Seed Cleaning and Drying - the stage before