|honey and oatmeal soap (tallow base)|
The water in soap making isn't actually part of the reaction. The soap reaction is between the oils and the caustic soda (sodium hydroxide). As the caustic soda is solid, it wouldn't disperse well and react evenly if we just added caustic soda granules to the oil. We dissolve the caustic soda in water so that we can easily mix the caustic soda with the oil to facilitate an even reaction. This is why measuring the exact amount of water to the mL is not important.
However, you do need to know approximately how much water to use. If you use too much water, the soap will be gluggy and take a long time to dry out and set completely. It will also lose a lot of weight as it cures, because all that extra water will evaporate. If you don't use enough water, then the caustic solution will be strong and the mixture will thicken very quickly, which can make it difficult to get into fancy moulds or do clever swirls and patterns before it sets (not to mention the danger of working with concentrated caustic solutions).
|pink clay soap, coffee grounds soap and honey oatmeal soap (recipe coming soon)|
Sometimes soapers will intentionally reduce the amount of water, which is called "water discounting". This is done to produce a harder bar more quickly (less water to evaporate), if other ingredients contain water (for example when adding purees) or to ensure that the soap gets hot enough to reach gel phase, and to prevent soda ash formation. Water discounting should be avoided when using ingredients that are known to produce hot mixtures, such as milk or honey.
So how much water should we use?
There is no rule for the perfect amount of water to use in soap, suggestions from various sources:
- 27% caustic soda to 73% water by weight
- water (g) = (caustic soda (g))*2 + 2
- 33% caustic soda in water for hard fats, up to 48% caustic soda in water for oils
- 300-330g water for every 1 kg of oil/fat
For less experienced soapers, its best to stick to the recipe and get some practice before experimenting with water discounting.
How much water do you use in your soap recipes? Have you tried experimenting with water discounting?