Scent Almanac
Liquid soap paste (KOH)
A potassium hydroxide (KOH) soap paste cooked until clear, then diluted with water into liquid hand or body soap. One batch of paste makes several bottles.
- Difficulty
- ●●●
- Time
- active 3–4 h · dilute overnight · settle 1–2 weeks
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.
- KOH solution gets hotter than sodium hydroxide and can bubble when the flakes hit the water. Add the KOH slowly, a little at a time.
- Use KOH (potassium hydroxide) only. Sodium hydroxide makes bar soap and won't dilute into liquid.
- Use a slow cooker you'll never cook food in again, and fill it no more than halfway because the paste can foam up.
Steps
- Check the recipe in the lye calculator with the KOH purity set correctly (usually 90%), and write down the weights. Put on protective gear and clear the room.
- Melt the oils in the slow cooker on LOW, to about 160°F (71°C).
- In a ventilated spot, slowly add the KOH to the water (never water to KOH) in a stainless steel or #5 PP container and stir until dissolved. It gets very hot and may fizz.
- Pour the KOH solution into the oils and stick-blend. KOH soap can look separated for a few minutes, then thickens quickly past trace into a taffy-like paste. Keep blending in bursts until it's too thick to blend.
- Cover and cook on LOW for about 3–4 hours, folding it over every 20–30 minutes. It will turn from opaque to a translucent, amber, petroleum-jelly-like paste.
- Clarity test: dissolve about 1 tsp (5 g) of paste in 2 tsp (10 g) of very hot distilled water. Clear or slightly hazy means it's done. Milky or with oil floating means keep cooking. Also check with a pH strip (9–10 is normal).
- Weigh the finished paste. It keeps for months in a sealed container, so you can dilute as you need it.
- Dilute: add hot distilled water at about 1.5–2 times the paste weight, cover, and leave it on LOW or overnight until dissolved, stirring occasionally. Add more water, a little at a time, until you like the thickness. Pure liquid soap stays fairly thin.
- When diluted and cooled, stir in the fragrance and any preservative.
- Let the diluted soap settle, covered, for 1–2 weeks. Any cloudiness sinks, and you can pour the clear soap off the top.
- Bottle it in pump bottles and label it.
KOH (90% purity)111.9 g · 3.9 oz
Water (distilled)288 g · 10.1 oz
2.6 : 1 water to lye
Fragrance15 g · 0.5 oz
Batch weight915 g · 32.3 oz
| Oil | % | Weight |
|---|---|---|
| Olive oil | 50.0 | 250 g · 8.8 oz |
| Coconut oil (76°) | 30.0 | 150 g · 5.3 oz |
| Castor oil | 20.0 | 100 g · 3.5 oz |
Bar qualities
Hardness
33
Cleansing
20
Conditioning
64
Bubbly
38
Creamy
30
Iodine
63
INS
145
Green bands are the usual ranges for a balanced bar. Liquid soap, castile and salt bars fall outside them on purpose.
More than 10% castor oil tends to make a soft, sticky bar.
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
- Cloudy liquid soap
- Unsaponified oil or hard-water minerals. Test the paste for clarity before diluting, use distilled water, and let it settle for 1–2 weeks. A little haze is harmless.
- Soap is too thin
- Normal for pure liquid soap. Next time use less dilution water. Salt thickens it only a little and can make it cloudy.
- Paste separated while cooking
- Stick-blend it back together and keep cooking. It usually comes together.
- Soap feels harsh or zaps
- Recheck the recipe, especially KOH purity (90% versus 100%). Don't use it until the pH reads 10 or under.