Liquid body wash
A mild liquid soap for the shower: olive and high-oleic sunflower oil make up more than half the oils, with coconut oil for lather and castor oil to hold it. Cooked as a potassium hydroxide paste, diluted to 20 % soap and thickened with a little salt water. Unscented.
- Skill
- Advanced
- Method
- Hot process
- Batch
- 500 g of oils about 1112 g of batter
- Hands-on
- 1 h 30 min
- Cure
- 2 weeks
- Gel phase
- In the pot it gels as it cooks
What you need
For 500 g of oils, which fills a lidded jar for the paste, then washed pump or squeeze bottles once diluted. Weigh everything, liquids included.
| Coconut Oil · 30.0 % | 150 g | 5.29 oz |
| Olive Oil · 45.0 % | 225 g | 7.94 oz |
| Castor Oil · 15.0 % | 75 g | 2.65 oz |
| Sunflowerseed Oil - High Oleic Acid · 10.0 % | 50 g | 1.76 oz |
| Potassium hydroxide (KOH) · the lye, 90 % pure; if your label says otherwise, weigh 118.1 g at 85 % or 105.7 g at 95 % | 111.6 g | 3.94 oz |
| Distilled water · for a 18 % lye solution | 500.0 g | 17.64 oz |
| Distilled water for the dilution · about this much, boiling hot: the finished soap should weigh 3002 g, so add 3002 g minus your cooked paste's weight, more if the cook drove off steam | 1890 g | 66.67 oz |
| Table salt, for the thickening solution · dissolved in the 80 g of hot distilled water below; you will use only a few grams of the solution per 100 g of soap | 20 g | 0.71 oz |
| Distilled water, hot, for the salt solution · for the method, not part of the formula | 80 g | 2.82 oz |
- Superfat
- 3.5 %
- Temperatures
- Lye solution cooled below 82 °C (180 °F), oils at 65 to 71 °C (150 to 160 °F), cooked on low
Method
-
Get ready
Put on sealed goggles, nitrile gloves and long sleeves, and keep them on until the paste is cooked. Weigh 150 g of coconut oil, 225 g of olive oil, 75 g of castor oil and 50 g of high-oleic sunflower oil into a slow cooker of 4.5 litres or more, 500 g of distilled water into a heat-proof jug and 111.6 g of potassium hydroxide flakes into a dry container, then close the flake tub at once. -
Make the lye solution
At an open window, add the flakes to the water a little at a time, stirring, never the water to the flakes. It fizzes loudly and gets very hot; let it cool below 82 °C (180 °F), and keep it away from aluminium, tin and zinc, which it attacks, giving off hydrogen. -
Warm the oils
Melt the coconut oil in the slow cooker on low, stir in the other oils and bring them to 65 to 71 °C (150 to 160 °F). -
Blend to a paste
Pour the lye solution into the oils and stick blend in bursts of a minute or two, stirring between them. The batter thickens, separates and thins, then comes back like thick apple sauce, often several times; with this much water and so much liquid oil it can take 45 minutes or more to hold together as a thick, opaque paste that no longer separates when you stop. -
Cover and cook
Put the lid on and leave the cooker on low. Check after 15 to 20 minutes and again 15 to 20 minutes later, stirring back any liquid that has separated, then stir every 30 to 45 minutes. -
Cook until translucent
Over 3 to 4 hours the paste turns golden and translucent from the edges inwards, softer than a low-water paste. It is ready to test when no opaque, creamy patches come up as you fold it over. -
Test a spoonful in boiling water
Stir 28 g (1 oz) of paste into 59 ml (2 fl oz) of boiling water until it dissolves, and let it cool. Clear or faintly hazy means the paste is done; milky, or with an oily film on top, means another hour of cooking and a second test. -
Weigh the paste
Turn off the cooker, let the paste cool and weigh all of it. It will weigh less than the 1111.6 g that went in, because steam left the pot, and the dilution needs the real figure. -
Work out the water
The paste holds 600.4 g of soap: the 500 g of oils plus the 100.4 g of pure potassium hydroxide in 111.6 g of 90 % flakes. At 20 % soap that makes 3002 g of body wash however much steam the cook drove off, so the water to add is 3002 g minus your paste's weight, about 1.70 g for every gram of paste if it lost none; the liquid soap dilution calculator does the same sum. -
Dilute it overnight
Break the paste into a large pot and pour on all but the last 200 g of that water, boiling hot. Stir gently without whipping up foam, cover it and leave it overnight; the next day, at room temperature, add the rest only if it is still thicker than you want. -
Thicken it with salt
Dissolve the 20 g of table salt in the 80 g of hot distilled water. Stir 1 g of this solution into a 100 g sample of the soap and wait an hour, repeating until a dose stops helping; then give the batch the same amount per 100 g, since past its peak more salt thins it again. -
Settle and bottle
Leave the soap covered for a week or two so any haze sinks, then pour the clear soap off the sediment into washed and dried bottles. -
Keep it clean
Diluted, this is four-fifths water, and it can grow bacteria and mould once they get in: never top up a half-empty bottle, and keep the rest as paste in a closed jar, diluting a little at a time. To keep diluted soap for long, or to sell it, it needs a preservative that works at pH 9 to 10, and soap for sale needs a challenge test as well.
Tips
- The lye assumes potassium hydroxide flakes of 90 % purity, the usual label figure. If your label says otherwise, enter it in the calculator before you weigh: with 95 % flakes the same weight takes the superfat from 3.5 % to about −1.9 %, a lye-heavy paste.
- The 3.5 % superfat is a margin for the spread in published saponification values, not oil for feel, and more oil only clouds the soap. With it the paste cannot come out lye-heavy, so leave out the borax or citric acid that older recipes neutralise with.
- To scent it, stir half a teaspoon of essential oil into 85 g of warm soap and wait half an hour: citrus oils especially can thin or cloud liquid soap, and they undo the salt thickening. If the sample holds, use 0.5 to 1 % of the diluted soap's weight.
- For a quicker, bubblier soap by the sink, see the liquid hand soap; for the mildest of all, the liquid castile. Use distilled water throughout: minerals in tap water form insoluble soaps that show as haze.
The oils
| Oil | Share |
|---|---|
| Coconut Oil | 30.0 % |
| Olive Oil (virgin / refined / olive oil) | 45.0 % |
| Castor Oil | 15.0 % |
| Sunflowerseed Oil - High Oleic Acid | 10.0 % |
How it is made
| Process | Hot process |
| Alkali | KOH |
| Superfat | 3.5 % |
| Water | 100 % of the oils |
| Iodine value | 62 |
| INS | 146 |
Why make it
A mild, pourable soap for the shower. Less coconut and more olive and high-oleic sunflower oil than a hand soap bring cleansing down to 20 and conditioning up to 64 on our scale, and oleic acid, about 42 % of the fatty acids, is what lets a little salt thicken it. It is unscented, in line with the American Academy of Dermatology's advice to wash dry skin with a gentle, fragrance-free cleanser in short, warm showers. Be clear about what it is, though: true soap, alkaline like any other, and a review of skin cleansers found that soaps disturb the skin's barrier more than mild synthetic cleansers do. The NHS advises people with eczema to wash with an emollient instead of soap, this one included. Many makers simply like knowing every ingredient in their wash; that is a preference, not a measured benefit.
Sources
- Dermatologists' top tips for relieving dry skin · American Academy of Dermatology
- Skin Cleansing without or with Compromise: Soaps and Syndets · Mijaljica D., Spada F. and Harrison I. P., Molecules 27(6):2010, 2022
- Atopic eczema: treatment · NHS
What tradition, makers' experience and research say about soaps like this, each labelled for what it is. It is not medical advice, and no soap treats a skin condition: if you have one, ask a doctor or pharmacist.
What the numbers say
- Lauric acid 14.7 %
- Myristic acid 5.7 %
- Palmitic acid 9.5 %
- Stearic acid 3.0 %
- Ricinoleic acid 13.3 %
- Oleic acid 42.2 %
- Linoleic acid 7.7 %
- Other 5.8 %
Saturated : unsaturated 37 : 63
Computed from the fatty acids of the fats above. The bands are what the craft has settled on, not chemistry — a bar outside one is not wrong.
From the guides
All guides
Liquid soap from potassium hydroxide paste
Real liquid soap from scratch: a potassium hydroxide paste cooked until it dissolves clear, diluted by weight, thickened with salt and kept free of microbes.
Sodium hydroxide, potassium hydroxide and dual lye explained
Why NaOH makes bars and KOH makes soft soap, converting between them, KOH purity, dual-lye recipes, and the calculator slip that turns a bar caustic.
Superfat and lye discount: why recipes leave some oil unsaponified
What superfat and lye discount mean, how the calculator applies them, where makers set them for each soap, and why oil added at trace isn't the oil left over.
Where these proportions come from
Our own formulation: less coconut oil than a hand soap, on the same potassium hydroxide system, with olive and high-oleic sunflower oil making up more than half the oils so that salt can thicken it. The superfat is 3.5 %, the lowest in half-point steps at which the published saponification ranges cannot leave the paste lye-heavy (at 0 % they could by 3.1 %), and the paste takes water equal to the oils. The method, a paste cooked in a slow cooker until translucent, tested in boiling water, diluted by weight and thickened with salt water, follows the liquid soap chapter of David Fisher's Complete Photo Guide to Soap Making, as our liquid soap guide does.
Formulation adapted from The Complete Photo Guide to Soap Making by David Fisher (Creative Publishing International, 2018). The method and notes are ours.