Making hard soap
The method requires three kettles or pans: two small kettles to hold the lye and the fat, and one large enough to contain both ingredients without boiling over.
1. Put the clean fat in a small kettle with enough water or weak lye to prevent burning, and raise the temperature to boiling.
2. Put the diluted lye in the other small kettle and heat it to boiling.
3. Heat the large kettle, and ladle in about one quarter of the melted fat. Add an equal amount of the hot lye, stirring the mixture constantly.
4. Continue this way, with one person ladling and another stirring, until about two-thirds of the fat and lye have been thoroughly mixed together. At this stage the mixture should have the consistency of cream and look the same throughout. A few drops cooled on a glass or ceramic plate should show neither separate globules of oil nor water droplets.
5. Continue boiling and add the remainder of the fat and lye alternately, taking care that there is no excess lye at the end of the process, when the mixture is thick and ropy and slides off the spoon or paddle.
6. Add salt to break up the creamy emulsion (mixture) of oils and lye. The soap then rises to the surface of the lye in granules and looks like milk curd. The spent lye contains glycerine, salt and other impurities, but no fat or alkali.
7. Pour the honey-thick mixture into cloth-lined soap moulds or shallow wooden boxes (the cloth prevents the soap from sticking to the moulds). Alternatively, the soap may be poured into a tub which has been soaked in water overnight to cool and solidify. Do not use an aluminium container because the soap will corrode it. Cover the moulds or tub with sacks to keep the heat in, and let the soap set for 2–3 days.
8. When cold the soap may be cut into smaller bars with a smooth, hard cord or a fine wire. It is possible to use a knife, but care is needed because it chips the soap. Stack the bars loosely on slatted wooden shelves in a cool, dry place and leave them for at least 3 weeks to season and become thoroughly dry and hard.
1) The mixture is poured into a mould lined with cloth. 2) The cold soap can be cut with a wire.
To improve hard soap
Better quality soap may be made by re-melting the product of the first boiling and adding more fats or oils and lye as needed, then boiling again. The time required for this final step will depend on the strength of the lye, but 2–4 hours’ boiling is usually necessary. If pure grained fat and good quality white lye are used, the resulting product will be a pure, hard white soap that is suitable for all household purposes. Dyes, essences or essential oils can be added to the soap at the end of the boiling to colour it or to mask the ‘fatty lye’ smell and give a pleasant fragrance.
Simple kitchen soap
Dissolve 1 can of commercial lye (sodium hydroxide) in 5 cups cold water and allow it to cool. Meanwhile mix 2 tablespoons (30 ml) each of powdered borax and liquid ammonia in half a cup of water. Melt 3 kg fat, strain it and allow it to cool to body temperature. Pour the warm fat into the lye water and, while beating the mixture, gradually add the borax and ammonia mixture. Stir for about 10–15 minutes until an emulsion is formed, and pour the mixture into a cloth-lined mould to cool.
Boiled hard white soap
Dissolve 0.5 kg potash lye in 5 litres of cold water. Let the mixture stand overnight, then pour the clear liquid into a second 5 litres of hot water and bring it to a boil. Pour in 2 kg of hot melted fat in a thin stream, stirring constantly until an emulsion is formed. Simmer for 4–6 hours with regular stirring, and then add 5 litres of hot water in which 1 cup of salt is dissolved. Test whether the mixture is ready by lifting it on a cold knife blade, to ensure that it is ropy and clear.
There is additional information available in the full Technical Brief:
- How to make soft soap (cold process)
- How to make large quantities of lye
- How to make tallow (animal fat prepared for use in soap making and candle making)
- Additional soap recipes
- Suggested solutions for common problems with soap making
- List of further resources
The Technical Brief was last updated by Tony Swetman. Practical Action uses simple technology to fight poverty and transform lives for the better. The full brief can be downloaded from the website. Go to http://practicalaction.org/practicalanswers and type ‘soap making’ in the search box.