About
Castor oil is a special case: it is made of 90% ricinoleic acid, a fatty acid found almost nowhere else. In small amounts it makes the lather denser, creamier and longer-lasting, and boosts the moisturising feel of the soap.
It is a "supporting" oil: it is usually used at 3 to 10% of the oils. Above 10 to 15%, the soap becomes soft and sticky and keeps less well.
It also tends to speed up trace, which matters for recipes with swirls or colours. It is widely used in shaving soaps and shampoo bars for its lather stability.
SAP value: 180 mg KOH/g, i.e. about 122 g of sodium hydroxide for 1 kg at 5% superfat.
Recommended usage rate
From 3 to 10% of the oils in the recipe.
Values
How much lye for 1 kg?
For 1,000 g of Castor Oil with 5% superfat:
These amounts apply to a soap made with this oil only. For a blend of oils, use the calculator.
Fatty acid profile
Soap qualities (oil used alone)
Values for a soap made with 100% of this oil, compared with the recommended range for a complete recipe.
Oils with a similar profile
Fats whose fatty acid composition is closest to this one: useful to find a substitute.