Castile Soap Recipe (100% Olive Oil Bar)
A gentle, long-curing bar made from nothing but olive oil, lye and water.
Formula not yet verified. These numbers haven't been re-run by a second maker. Don't make this batch until this notice is gone.
- Yield
- 10 bars
- Method
- Cold process
- Difficulty
- Beginner
- Cure
- 6 months
- Superfat
- 5%
- Lye conc.
- 35%
On this page
Castile is the simplest soap you can make: one oil, lye and water. The catch is time. A pure olive oil bar takes days to unmold and months to cure, and this recipe uses a little less water than usual to speed the first part up.
Why this recipe works
- Olive, 100%. The mildest common soap oil. It makes a hard bar in the end, but it gets there slowly.
- 35% lye concentration. Less water than usual so the soft batter firms up enough to unmold.
Ingredients
| Oil | % | Grams | Ounces |
|---|---|---|---|
| Olive oil | 100% | 1,000 g | 35.27 oz |
| Lye solution | |||
| Sodium hydroxide (NaOH) 5% superfat | 128 g | 4.52 oz | |
| Distilled water 35% lye concentration | 238 g | 8.40 oz | |
Instructions
Step 1: Gear up and make the lye solution
Put on goggles and gloves. Add the lye to the water, never the reverse, and stir until clear. Let it cool to around 100°F (38°C).
Step 2: Warm the olive oil
Bring the olive oil to roughly the same temperature as the lye solution.
Step 3: Blend to trace
Pour the lye solution into the oil and stick blend in bursts. Pure olive oil traces slowly, so expect 5–10 minutes of blending.
Step 4: Pour, then wait
Pour into the mold and leave it at room temperature. Castile can take 3–5 days to firm up enough to unmold.
Step 5: Cut and cure
Cut once it's firm and cure for at least 6 months. Young castile works but feels slimy; the long cure makes a hard, mild bar.
Variations
Bastille
Swap 10–20% of the olive for coconut oil for more lather and a faster unmold.
Unscented
Castile is popular plain. Skip the fragrance if it’s for sensitive skin.
Herbal
Infuse the olive oil with calendula petals before weighing.
If something goes wrong
- Still soft after 3 days
- Normal for castile. Wait. Next time try a higher lye concentration.
- Slimy lather
- It needs more cure time. Castile lather improves for a year.
FAQ
Why does castile soap take so long to cure?
Olive oil makes soap that holds water and hardens slowly. The long cure lets water evaporate and the bar harden, which also makes the lather less slimy.
Is castile soap good for sensitive skin?
Many people find it very gentle. As with any soap, patch test first; we don't make skin-condition claims.
Can I use pomace olive oil?
Yes. Pomace traces faster than extra virgin, which can make the batch quicker to work.
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