How to Make Liquid Soap from Scratch with KOH

Why Liquid Soap Needs KOH

Bar soap is made with sodium hydroxide (NaOH). True liquid soap is made with potassium hydroxide (KOH), which produces a soft soap that dissolves in water. You cannot make real liquid soap by using NaOH and adding more water, or by grating a bar into water; those give a gloopy, cloudy gel.

How It Works

Liquid soap is made in two stages. First you make a thick soap paste by cooking oils and KOH together, like hot process soap. Then you dilute that paste with hot water until it is the thickness you want.

Step by Step

• Calculate your recipe with KOH selected. Most KOH is 90% pure, and a good calculator adjusts for that
• Use a low superfat of 0–3%, since extra oil makes liquid soap cloudy
• Melt the oils in a slow cooker, add the KOH solution and stick blend. KOH soap takes longer to trace than bar soap
• Cook on low, stirring every 20–30 minutes. The paste goes through stages and ends up like thick, translucent taffy. This can take 2–4 hours
• Test it: dissolve a small piece in hot water. If it is clear, it is done. If it is milky, cook longer
• Dilute the paste with about 1.5–2.5 times its weight in hot distilled water. Add the water gradually and let it sit overnight to dissolve
• Add fragrance once the soap has cooled

Get a liquid soap recipe with exact KOH amounts →

Common Problems

• Cloudy soap: usually too much superfat, undercooked paste, or hard water. Use distilled water and a low superfat
• Too thin: dilute less next time. Salt thickens some liquid soaps, but add a tiny amount at a time because too much makes it thinner
• Separation: undercooked paste. Recook it and test again
• Diluted liquid soap has a high pH that resists spoilage, but if you add water-based extras such as herbal teas or aloe, you may need a preservative