Clean oilseed of stems, leaves, stones and soil, then dry it to 8-10% moisture before pressing: drier seed gives less oil and wetter seed clogs the press. Drying 100 kg from 14% to 9% moisture removes about 5.5 kg of water, which takes 2-3 days spread thin in the sun and turned regularly, and sunflower seed should be dehulled before it is crushed.
Part of Oil Pressing at Scale
The first steps of oil making: removing foreign matter, drying the seed to pressing moisture, and dehulling sunflower.
Clean First, Because A Stone Does Real Damage
The carrier’s first step is to remove all foreign material: stems, leaves, stones and soil, by sieving through mesh or winnowing. A stone in the crusher chips its faces and can spark; soil adds grit to the oil and shortens its life. Discard any seed that is moldy, shriveled or insect-damaged, because it makes rancid, foul-tasting oil (Oil Extraction).
Dry To 8-10% Moisture
The carrier asks for 8-10% moisture, and warns that over-dry seed yields less oil while wet seed clogs the press. Seed that is too wet also molds in storage. Spread seed thinly on trays or clean cloth in the sun for 2-3 days, turning regularly. The corpus oil-extraction page adds a bite test: a dry seed snaps cleanly rather than bending or feeling chewy, and an alternative of 4-6 hours in a cooling clay oven at 80-100 degrees C.
How Much Water Leaves
Moisture is measured on a wet basis: water mass over total mass. Seed at 14% moisture holds 14 kg of water in 100 kg and 86 kg of dry matter. At 9% moisture the 86 kg of dry matter is 91% of the mass, so the mass is 86 / 0.91 = 94.5 kg and the water removed is 100 - 94.5 = 5.5 kg. To check a batch, weigh a 100 g sample, dry it until its weight stops falling and weigh again; if it falls to 91 g the moisture was (100 - 91) / 100 = 9%.
Dehull Sunflower, Skip Others
The carrier says sunflower seed should be dehulled before pressing. Hulls can be pressed with the seed, but the yield is lower and the oil quality reduced. Two methods: beat the seed in a bucket with a paddle and winnow off the lighter hulls, or pass the seed once through a grain mill set wide, which cracks the hulls without pulverizing the kernels (Specialty Grinds covers a similar hulling pass for oats). Hulls are good mulch or fuel.
What You Need
- Screens of two or three meshes and a winnowing space (Winnowing)
- Drying trays or clean cloth, a dry sunny place, and a rack to bring them in at night
- A scale and a warm place for the weigh-and-dry sample
Method: Prepare A Batch
Step 1: Sieve and winnow to remove stems, stones and soil; hand-pick moldy and damaged seed.
Step 2: Dry in thin layers, turning at least twice a day; bring the trays in before dew or rain.
Step 3: Test by bite and by weight until the seed is at 8-10%.
Step 4: Dehull sunflower and winnow the hulls away.
Step 5: Store dry in a sealed container until pressing, and press within a few weeks.
Common Mistakes
- Pressing wet seed. It clogs the press and the oil spoils.
- Over-drying in an oven. Over-dry seed yields less oil and may degrade the oil.
- Leaving seed out overnight. It re-absorbs damp.
Dust, hot ovens and sharp screens
Seed and hull dust is combustible: sweep it, keep open flame out of the cleaning area and never test for dust with a flame. Do not leave seed in an oven unattended. Moldy seed dust irritates the lungs, so wear a damp cloth over the mouth and nose when cleaning damaged seed.
What’s Next
- Learn next: Crushing and Heating (Expeller Method) - the next steps
- Combine with: Grain Storage - the same moisture discipline for storage