Olive and nut oils come from trees, so they pay back slowly: an olive tree takes 5-12 years to bear and then gives 20-50 lb of oil, and walnut oil takes 2.2-2.9 kg of kernels a litre at 350-450 mL of oil per kilogram. They are fine oils worth planting where the climate allows, but a village needing 1,100-2,200 lb of oil a year cannot rely on them in its first years.
Part of Oil Pressing at Scale
Tree oils for a village: olive in Mediterranean climates, walnut and hazelnut in temperate ones, what each yields, how the fruit or nut is processed and what the tree count has to be.
Olive Is A Mediterranean Crop With A Long Wait
The carrier says olives belong to Mediterranean climates only, with mild winters and hot, dry summers, and that a tree takes 5-12 years to begin bearing significantly. Do not try to grow them outside that range. Fruit is 15-25% oil by weight. The carrier gives 20-50 lb of oil from a mature tree, and the fruit is crushed in a stone mill and the paste pressed in a screw or lever press.
The oil figure is stated per tree with no statement of the period or of whether it is oil in the fruit or oil pressed; read it as one year’s crop and an upper figure and expect a press to recover 50-70% of the oil in the fruit. A village needing the carrier’s 1,100-2,200 lb of oil a year needs 1,100 / 50 = 22 up to 2,200 / 20 = 110 mature trees on the carrier’s figures.
Nut Oils Are Rich But Costly In Kernels
The corpus table gives walnut at 60-65% oil with 350-450 mL of finished oil per kilogram of kernels, and hazelnut at 55-60% with 300-400 mL per kilogram (Oil Extraction). Those yields are 50-70% of the oil the nuts hold. The kernel needed per litre is the reciprocal:
- Walnut: 1 / 0.45 = 2.2 kg to 1 / 0.35 = 2.9 kg of kernels a litre
- Hazelnut: 1 / 0.40 = 2.5 kg to 1 / 0.30 = 3.3 kg a litre
A year’s minimum of 1,100 lb of oil is 1,100 x 0.4536 = 499 kg, which at 0.92 kg/L is 499 / 0.92 = 542 litres. That is 542 x 2.2 = 1,192 kg up to 542 x 2.9 = 1,572 kg of walnut kernels, over a tonne of shelled nuts. Nut oil is a supplement for the village, not its base fat.
What You Need
- Mature trees, or a plan for planting that accepts the years to bearing
- A stone crusher that is not the grain millstone pair; the paste is oily and wet and will clog and glaze the fine furrows of a grain mill
- A press (Screw Press Design) and cloth bags
Method: Olive Oil
Step 1: Harvest the fruit ripe and process it soon after, because the fruit deteriorates once picked.
Step 2: Crush whole fruit, stones and flesh, to a paste in a stone mill.
Step 3: Press the paste in cloth in a screw or lever press, with gradual pressure.
Step 4: Settle and decant. Olive oil will separate from water and fruit juice (Settling and Cloth Filtration).
Method: Nut Oil
Step 1: Shell and pick the kernels, discarding any moldy, shriveled or insect-damaged ones.
Step 2: Dry. Kernels must be dry before pressing.
Step 3: Grind to a coarse paste, warm gently and press. Do not scorch the paste.
Step 4: Store small amounts, because tree-nut oils spoil more quickly than the olive oil in a cool store (a general rule recalled, not a corpus figure).
Common Mistakes
- Planting olives for next year’s oil. The first useful crop is 5-12 years away.
- Counting the oil in the fruit. The press leaves 30-50% behind.
- Pressing in the grain mill. The oily paste ruins the stones’ furrows.
Allergy and moving machinery
Nut oils can cause severe allergic reactions in people allergic to the nut; label every jar and tell the kitchen. Crushers and presses crush hands: guard them and stop the machine before clearing a jam. Nut and seed dust is combustible, so keep open flame out of the processing area.
What’s Next
- Learn next: Flax and Linseed - the fibre-and-oil crop
- Combine with: Oil Yield per Acre by Crop - tree and field crops compared