What is saponification?
Short answer
It's the reaction between oils and lye that turns them into soap. As the book says: there is no soap without lye.
Explanation
Oils react with an alkali, sodium hydroxide for bars, and become soap. The chemical conversion happens within 24–48 hours. Curing then lets water evaporate, the pH stabilize and the bar harden.
Each oil needs a specific amount of lye, set by its saponification (SAP) value. That's why the soap calculator's first job is working out exactly how much lye your oils need. Oils also react at different speeds: lauric-rich coconut saponifies fast, while oleic-rich olive oil is slow, which is why Castile traces and cures so slowly.
What to do
- Enter acidic additives (juice, purées, citric acid) in the calculator: they use up some lye.
- Adjust the oils, never the lye, to change how a bar behaves.
Source: The Big Book of Homemade Soap — Interpreting Soap Calculator Quality Values