Plant Oils

Part of Soap Making

Which plants yield usable oils, how to extract them, and how their properties shape the soap you make.

Why This Matters

Fat is half the soap equation. Without a reliable fat source, you have lye and nothing to put it to. In a rebuilding scenario, animal fats are useful but limited — they require slaughter or rendering, and in lean times, tallow and lard compete with nutrition. Plant oils sidestep that constraint. If you can grow sunflowers, press olives, crack coconuts, or harvest rapeseeds, you have a renewable, scalable soap feedstock that doesn’t compete with your food supply in the same way.

Beyond availability, different plant oils produce radically different bars of soap. An all-coconut-oil soap is rock-hard, lathers furiously, but dries out skin. An all-olive-oil soap (Castile) is gentle and conditioning but soft, slow-lathering, and takes months to harden properly. Blending oils lets you engineer the soap you actually need — hard bars for field use, lathering bars for washing clothes, conditioning bars for medical care. Understanding each oil’s properties gives you that engineering control.

Finally, knowing how to extract and store plant oils without refrigeration or industrial equipment is a foundational skill that extends well beyond soap. The same pressed oil you use in soap is your cooking oil, your lamp fuel, your wood preservative, and your skin salve. Mastering oil extraction once pays dividends across dozens of applications.

Plants That Produce Usable Soap Oils

Not every oily plant is practical for soap. You need: sufficient oil content (above ~20% by weight), a viable extraction method with simple tools, and an oil that saponifies reliably. The following are proven options ranked by practicality in most temperate-to-tropical climates.

Olive (Olea europaea) — 15–20% oil by fresh weight of fruit, ~30% of dry flesh. Mediterranean staple, but viable in any frost-light climate. Produces a soft, conditioning soap (Castile soap) that is very gentle on skin. Low lather volume, slow cure, but considered the gold standard for skin-safe soap. Press ripe olives; the oil separates from water with settling or gentle heating.

Sunflower (Helianthus annuus) — Seeds contain 40–50% oil. Grows in most temperate regions with a long summer. Produces a soft, conditioning soap similar to olive but with higher linoleic acid content. Good for skin, moderate lather. Easy to press with a simple screw press.

Rapeseed/Canola (Brassica napus) — Seeds contain 40–45% oil. Extremely cold-hardy, producing oil in climates too cold for olive or sunflower. Produces a moderately conditioning soap with reasonable hardness. One of the most important soap oils in historical northern Europe.

Coconut (Cocos nucifera) — Dried copra contains 60–70% oil. Tropical regions only. Produces the hardest, highest-lathering bar possible. Essential for any soap formula that needs to lather in saltwater. The dominant oil in commercial soap. Too much coconut oil alone makes skin-drying soap — cap at 30–35% of your oil blend.

Palm (Elaeis guineensis) — Tropical. Palm fruit pulp: ~45% oil. Produces a very hard bar with stable lather — the other dominant commercial soap oil. Ethically controversial in modern times due to deforestation, but in a rebuilding scenario it is simply a productive oil palm. Red palm oil (from fruit pulp) contains high carotenoids; refined palm oil (lighter colored) is neutral. Both work for soap.

Castor (Ricinus communis) — Seeds: 40–50% oil. Important caveat: the plant produces ricin (extremely toxic), but this is in the seed meal after pressing, not in the oil itself. Cold-pressed castor oil is safe and uniquely useful in soap — it dramatically improves lather and helps bind other oils. Use at 5–10% of your blend. Do not consume the seed meal; dispose of it safely.

Linseed/Flax (Linum usitatissimum) — Seeds: 40–44% oil. Grows in cool climates. Produces a soft, skin-conditioning soap, but linseed oil is highly unsaturated and goes rancid quickly — in soap and in storage. Use in small percentages only, and use fresh oil. Soap made with high linseed ratios develops dreaded orange spots (rancidity) within weeks.

Hemp (Cannabis sativa) — Seeds: 25–35% oil. Similar properties to linseed — conditioning but prone to rancidity. Best used at 10–15% of blend, combined with more stable oils.

Pumpkin/Squash (Cucurbita spp.) — Seeds: 35–50% oil. Available wherever squash is grown. Soft, conditioning soap. Seed oil is easy to extract by hand-pressing dried seeds. Good backup oil when primary crops fail.

Extraction Methods

Cold Pressing

The simplest mechanical method. Seeds or fruit are crushed and the oil squeezed out without heat. Produces the highest-quality oil with full nutrient content preserved.

Crude hand method: Dry seeds thoroughly (moisture causes mold and rancidity). Grind in a stone mortar or between flat stones until you have a rough paste. Wrap the paste in clean cloth and twist tightly, squeezing oil into a bowl. This is slow and recovers only 40–60% of available oil, but requires no tools beyond rocks and cloth.

Screw press (edge runner press): A wooden or iron screw tightened against a perforated basket containing ground seed paste. Build the basket from closely-spaced wooden slats or drill many small holes in a wooden cylinder. The screw can be a carved wooden thread or a wrought-iron bolt. Recovery improves to 75–85%. This is the practical workhorse for community-scale oil production.

Wedge press: A tapered wooden wedge driven by a mallet into a slotted frame holding the wrapped seed cake. Cruder than a screw press but buildable from basic timber. Used in Mediterranean olive production for centuries.

For olives specifically: crush the whole olives (pit and all) with a stone roller or between stones, then press the paste. The resulting liquid is an emulsion of oil and water — allow it to settle in a shallow pan for 1–2 hours; oil rises to the top and can be skimmed off. Or gently heat the emulsion to 40°C, which breaks the emulsion faster.

Hot Pressing and Rendering

For oils resistant to cold pressing (some nut oils), or when you want maximum yield:

Heat the seed paste to 60–80°C while pressing, or pre-roast seeds briefly before crushing. This ruptures more oil cells but degrades some nutrients and introduces color. For soap purposes, hot-pressed oil works perfectly; for eating, cold-pressed is superior.

Water extraction: Boil crushed oily seeds or coconut flesh in water for 30–60 minutes. Oil floats on the surface; skim it off or allow the pot to cool and the oil to solidify on top (coconut oil, palm oil). This is the traditional method for coconut oil in tropical regions. Low yield compared to pressing but requires no equipment beyond a pot.

Crude Refining

Raw-pressed oils often contain plant matter, water, and pigments that can affect soap color and shelf life. For soap use, basic settling is usually sufficient:

1. Let pressed oil stand in a tall container for 24–48 hours at room temperature.
2. Sediment sinks; surface foam can be skimmed.
3. Carefully pour or siphon off the clear oil from the top, leaving sediment behind.
4. If the oil appears cloudy (water emulsion), gently heat to 60°C and stir in a small amount of salt (1% by weight). The salt breaks the emulsion; water and salt sink, oil clears.

You do not need bleached, deodorized, or refined oil for soap — basic settled oil is fine. Dark green olive oil makes green soap. Red palm oil makes orange soap. This is not a defect.

Oil Properties for Soap

Each oil contributes specific characteristics to the final bar. You need to balance four key qualities:

Hardness: How firm the bar is when cured. Comes primarily from saturated fatty acids (palmitic, stearic). Coconut and palm oils are hardest. Olive and sunflower are softest. A very soft bar is inconvenient and wastes quickly in use.

Cleansing: Stripping power — how well the soap removes grease and dirt. Coconut oil provides most of this. Too much cleansing makes skin dry and tight. Too little and the soap doesn’t cut grime effectively.

Lather quality: Coconut and castor oils produce abundant, fluffy lather. Olive oil produces creamy, lotion-like lather. Lard and tallow produce stable but unremarkable lather. In cold or hard water, lather is harder to achieve — coconut oil helps.

Conditioning: Skin feel after washing — whether skin feels moisturized or stripped. Olive, sunflower, hemp, and castor oils contribute conditioning. Coconut oil in excess removes conditioning.

Simplified SAP values: Each oil requires a specific amount of lye to fully saponify. This ratio (grams of NaOH per gram of oil) is called the saponification value. You don’t need precise numbers to start — use established recipes — but understand that substituting oils means adjusting lye amounts, not just swapping fat volume for volume. If you replace olive oil (SAP ~0.134) with coconut oil (SAP ~0.190), you need significantly more lye.

Balanced Oil Blends

Three reliable starting formulas using oils likely available in most regions:

Basic temperate blend (olive/sunflower/tallow):

• 40% olive or sunflower oil
• 40% lard or tallow (if available — improves hardness)
• 20% coconut oil (if available — improves lather) If no coconut: 60% olive/sunflower, 40% lard/tallow. Harder bar, less lather, but solid soap.

Tropical blend (coconut/palm):

• 35% coconut oil
• 50% palm oil
• 15% castor oil Produces a very hard, long-lasting bar with excellent lather. The classic West African formula.

All-olive Castile (no animal fat, no tropical oils):

• 100% olive oil Simple but requires a 6-month cure for the bar to harden properly. Lather is minimal at first but improves with age. Extremely gentle — suitable for infant skin and medical use.

Cold-climate blend (rapeseed/lard):

• 50% rapeseed oil
• 35% lard or tallow
• 15% castor oil (if available) Practical for northern Europe, Canada, highland Asia. Good hardness, moderate lather.

Storing Oils to Prevent Rancidity

Rancid oil makes soap that smells bad, develops orange or brown spots, and can irritate skin. Oxidation is the enemy.

Reduce oxygen exposure: Store oil in filled containers with minimal air space. If a container is partially empty, transfer to a smaller container. Seal tightly.

Keep cool and dark: Heat and light accelerate oxidation. Ceramic crocks, buried stone jars, or root cellar storage dramatically extend shelf life. Even cool room temperature (15–18°C) versus direct sunlight makes months of difference.

Shelf life by oil type:

• Coconut and palm: 18–24 months sealed, very stable
• Olive and rapeseed: 12–18 months
• Sunflower and hemp: 6–12 months
• Linseed: 3–6 months (use fresh or don’t bother storing)

Warning signs of rancidity: Smell — off, paint-like, crayon-like odor. Color change — darkening or cloudiness where there was none. If oil smells clearly rancid, don’t use it for soap. The rancidity will carry through saponification and produce unpleasant, irritating bars.

Antioxidant additions: A few drops of vitamin E oil (from any seed oil capsule, if available) mixed into your stored oil dramatically slows oxidation. Rosemary oleoresin extract (simmered rosemary strained from oil) serves the same function with primitive means.

Regional Oil Availability Guide

You will use what grows near you. Plan your oil supply around your climate:

• Mediterranean / North Africa / Middle East: Olive is dominant. Sesame is available and works well. Castor grows as a weed in disturbed soil.
• Sub-Saharan Africa: Palm oil and coconut are abundant. Shea butter (from shea tree nuts) works excellently in soap at 20–30% of blend.
• South and Southeast Asia: Coconut oil dominates. Palm available. Rice bran oil is plentiful as a byproduct of rice milling and makes decent soap.
• Temperate Europe and North America: Lard and tallow historically dominant, supplemented with linseed and rapeseed. Sunflower widely growable. Import substitution with castor bean (grows in warm summers) is viable.
• Tropical Americas: Coconut and palm available. Avocado oil (seeds: ~15% oil) is a luxury conditioning option.

Common Mistakes

• Using rancid oil: Results in spotted, smelly soap. Always smell oil before using it.
• Substituting oils without adjusting lye amount: Each oil needs a different amount of NaOH. Don’t swap oils by volume and expect the same recipe to work.
• Using too much linoleic-rich oil (linseed, hemp, sunflower): These oxidize after saponification too, causing dreaded orange spots (DOS — dreaded orange spots) in cured soap.
• Not drying seeds before pressing: Wet seeds yield less oil and the oil is cloudy with water emulsion; it separates and causes issues in soap.
• Pressing olive pits separately: The pit oil is bitter and lower quality. Crack pits out if you want premium olive oil; crush whole olives only if you want maximum yield at lower quality.
• Storing oil in plastic long-term: Plastic off-gasses into oil and oil oxidizes through thin plastic walls. Use glass, ceramic, or food-grade metal.

Key Takeaways

• The most practical soap oils by climate: olive/sunflower (temperate), coconut/palm (tropical), rapeseed/lard (cold climates)
• Cold pressing in a screw press is the workhorse extraction method — achieves 75–85% oil recovery
• Balance four properties in your blend: hardness, cleansing, lather, conditioning
• Substituting oils requires recalculating lye amount — don’t substitute by volume without adjustment
• Highly unsaturated oils (linseed, hemp, high-linoleic sunflower) cause rancidity in finished soap — limit to 10–15% of blend
• Store oil sealed, cool, and dark; use within 6–18 months depending on oil type
• Castor oil at 5–10% of any blend dramatically improves lather quality