How to Make Liquid Soap at Home: Two Step-by-Step Methods

There are two ways to make your own liquid soap. The simplest: dissolve grated soap in hot water, with twenty minutes of work and a night's rest. The most advanced: cook oils with potassium hydroxide, as soap makers do, to obtain a concentrated paste that you then dilute. Here are both, step by step.

At a glance

• Method 1, grated soap: 20 minutes of work, one night's rest, no caustic product
• Method 2, potassium hydroxide: 3 to 4 hours of cooking, one night of dilution, one to two weeks' rest
• Why potassium hydroxide: sodium hydroxide makes hard soaps, potassium hydroxide makes soft and liquid soaps

Method 1: making liquid soap from a grated bar of soap

For about 500 ml of liquid soap:

• 50 g of Aleppo soap or Marseille soap, with no added fragrance
• 500 ml of boiled or demineralised water
• 1 teaspoon of vegetable glycerine, optional, for extra softness

1. Grate the soap finely, using a kitchen grater kept for this purpose
2. Heat the water without letting it boil, then add the grated soap
3. Stir over a low heat until all the flakes have melted
4. Leave to rest overnight. The mixture turns into a gel as it cools: this is normal
5. Blend to smooth the texture. Too thick? Add a little hot water. Too runny? Use more soap next time
6. Pour into a clean bottle, adding the glycerine if you are using it

This soap contains a lot of water and no preservative: it does not keep well. Make a little at a time, with clean utensils, and use it up quickly.

Method 2: real liquid soap made with potassium hydroxide

This is the method soap makers use for potassium-based liquid soaps. The oils are cooked with potassium hydroxide until you get a translucent, highly concentrated paste, which is then diluted in water. Potassium hydroxide is corrosive: keep your goggles, gloves and long sleeves on from weighing right through to dilution.

Equipment

• Digital scales accurate to 0.1 g
• Safety goggles, nitrile gloves, long sleeves
• A heat-resistant stainless steel or hard plastic (PP or HDPE) container for the potassium hydroxide, ⚠️ never aluminium
• pH test strips
• A slow cooker, or a large, deep stainless steel pan used as a bain-marie: the paste swells during cooking
• A stick blender, a spatula, a thermometer

Ingredients

The quantities are calculated for a 3% superfat and 90% pure potassium hydroxide, the most common form. Coconut oil provides the lather, olive oil the mildness.

⚠️ Potassium hydroxide of a different purity, another oil or another quantity: recalculate with our free soap calculator, selecting “potasse” (KOH).

Method

1. Make the potassium hydroxide solution. Start with cold water and pour the potassium hydroxide into the water, never the other way round, a little at a time, stirring, with the window open and without breathing in the fumes. The mixture becomes very hot
2. Heat the oils in the slow cooker to about 70 °C, until the coconut oil has melted
3. Mix: pour the potassium hydroxide solution into the oils and blend in pulses. The paste thickens until it becomes very firm, like modelling clay: keep stirring it with the spatula
4. Cook for 2 to 4 hours on a low heat, with the lid on, stirring every 30 minutes. The paste turns translucent and honey-coloured
5. Do the test: dissolve a hazelnut-sized piece of paste in a little very hot water. If it is clear or only slightly hazy, cooking is usually finished: with a 3% superfat, a slight haze is normal. If it is milky, with drops of fat, continue for 30 minutes and test again
6. Dilute. Add 1.5 to 2 times the weight of the paste in hot demineralised water, cover and leave to dissolve overnight. Adjust with water until you reach the texture you want
7. Check the pH with a strip. Soap is naturally alkaline, around 9 to 10. If it is clearly higher, do not use it on skin and check your calculation
8. Leave to rest for one to two weeks before use: impurities settle at the bottom and the soap becomes clearer

The undiluted paste contains less water than the diluted soap and keeps better: store it in a closed jar and dilute only part of it at a time. This is also the principle behind black soap, a paste made from potassium hydroxide and olive oil, which you can discover in our black soap recipes.

Safety: potassium hydroxide and sodium hydroxide

Caustic potash (potassium hydroxide) is corrosive to skin and eyes. On skin: remove contaminated clothing, rinse immediately with water for at least 15 minutes, then see a doctor. In the eyes: rinse immediately under running water for at least 15 minutes and call the emergency services (999 in the UK, 112 in the EU) or a poison centre without waiting until you have finished rinsing. Store it closed, labelled and out of the reach of children.

This soap is for your personal use. To sell it, cosmetics regulations require in particular a responsible person, a product information file with a safety assessment, good manufacturing practice, compliant labelling and notification on the European CPNP portal.

Frequently asked questions

Can you make liquid soap with sodium hydroxide?

No. Sodium hydroxide makes hard soaps. Liquid soap is made with potassium hydroxide, or by dissolving an already finished hard soap in water.

My homemade liquid soap is too thick or has turned into a gel: what should I do?

This is normal with grated soap: it gels as it cools. Blend it, then add hot water little by little, stirring, until you reach the texture you want.

How long does homemade liquid soap keep?

Not well, as it contains no preservative. Make a little at a time, with clean utensils and boiled water, and use it up quickly. If you have the slightest doubt about its smell or appearance, throw it away.

Which soap should I grate to make liquid soap?

A simple soap with no added fragrance: Aleppo soap or Marseille soap. Aleppo soap gives a liquid lightly scented with laurel.

Why does my potassium hydroxide paste stay cloudy?

With a 3% superfat, a slight haze is normal: the free oil clouds the liquid. If the paste stays milky and greasy in the test, cooking is not finished: keep going.

No time to cook?

Our liquid soaps are potassium-based soaps, made in France: Tradition liquid Aleppo soap, organic liquid Aleppo soap with 15% laurel, organic pure olive liquid Marseille soap. The whole range: liquid soaps. For more recipes: how to make Aleppo soap, Marseille soap and a solid shampoo bar.