Scent Almanac
Castile (olive oil) soap
A traditional 100% olive oil soap: very gentle and mild, slow to trace and soft at first, with a long cure that turns it hard and silky.
- Difficulty
- ●●○
- Time
- active 1.5 h · cut in 2–4 days · cure 3–6 months or longer
Safety first
- Wear chemical-splash goggles (not just glasses), nitrile or rubber gloves, long sleeves and closed shoes from the moment the lye container opens until the raw soap is put away.
- Mix lye solution in a well-ventilated spot: under a running range hood, by an open window, or outdoors. Don't lean over it. The fumes in the first minute sting the lungs.
- Always add lye to water, never water to lye ('snow falls on the lake'). Pouring water onto lye can erupt and splash boiling caustic liquid.
- Mix and hold lye in a heavy stainless steel or #5 PP plastic container, and stir with stainless or silicone. NEVER use aluminum, which reacts violently and gives off hydrogen gas. Avoid glass, which lye etches and can crack.
- Keep children and pets out of the room until the lye, raw soap and all tools are cleaned up and put away.
- Keep vinegar handy for wiping lye or raw soap off counters and floors. It is for surfaces only. For skin and eyes, use plain running water: flush for 15 minutes. For eyes, flush for 15 minutes and get medical help.
- Weigh everything (oils, water and lye) on a digital scale in grams. Never measure by volume.
- Run every recipe through a lye calculator before you make it, including this one and any time you swap an oil. The preset here opens in the app's lye calculator.
- Store lye sealed, labeled and out of reach. Raw soap stays caustic for a day or two, so wear gloves to unmold and cut it.
Steps
- Check the recipe in the lye calculator and write down the weights. Put on protective gear and clear children and pets from the room.
- In a ventilated spot, add the lye to the water (never water to lye) in a stainless steel or #5 PP container, stir until clear, and let it cool.
- Warm the olive oil gently. Bring the lye solution and oil to about 90–110°F (32–43°C).
- Pour the lye solution into the oil and stick-blend in bursts. Olive oil traces slowly, so blend for 1–2 minutes, rest, and repeat. It can take 10 minutes or more to reach light trace.
- Stir in the essential oil at light trace, then pour into the mold and tap out air bubbles.
- Cover it loosely. Castile doesn't need forced gel, and insulating it can cause a soft center, so leave it at room temperature.
- Castile stays soft and sticky for a while. Unmold after 2–4 days, when it feels firm like cheddar, then cut. Wear gloves.
- Cure on a rack with airflow for at least 3–6 months, or longer. It gets harder, milder and longer-lasting with time, and many makers cure a year.
- Before use, do the zap test or check with a pH strip (9–10 is normal).
- Expect a slimy feel when wet and a low, lotion-like lather. That's normal for castile. Keep it on a draining soap dish.
NaOH128.2 g · 4.5 oz
Water (distilled)238 g · 8.4 oz
1.9 : 1 water to lye
Fragrance30 g · 1.1 oz
Batch weight1396 g · 49.3 oz
| Oil | % | Weight |
|---|---|---|
| Olive oil | 100.0 | 1000 g · 35.3 oz |
Bar qualities
Hardness
17
Cleansing
0
Conditioning
82
Bubbly
0
Creamy
17
Iodine
85
INS
104
Green bands are the usual ranges for a balanced bar. Liquid soap, castile and salt bars fall outside them on purpose.
Lye safety: wear goggles and gloves. Add lye to water, never water to lye, in a heat-safe stainless or #5 plastic container, with good ventilation and no children or pets nearby. Always double-check a lye amount with a second calculator before you make soap.
If something goes wrong
- Won't reach trace
- Normal for olive oil. Keep blending in bursts, with rests to protect the blender motor. Warming the batter a little or using a lower water amount (higher lye concentration) speeds it up.
- Too soft to unmold
- Give it more days in the mold. Next time, use a slightly higher lye concentration or a little sodium lactate.
- Slimy bars
- Characteristic of castile. A longer cure and a draining soap dish help a lot.
- False trace (thick, then separates)
- The oil or lye was too cool. Warm both to about 100°F (38°C) and keep blending until it stays emulsified.
- Soda ash (white powdery film on top)
- Harmless: unreacted lye met air before saponification finished. Steam it off, plane it off, or wash the bar once. Prevent it by spritzing the fresh top with 91–99% isopropyl alcohol, covering the mold, and using a higher lye concentration.