How do different oils affect the final soap?
Short answer
Each oil's fatty acids shape the bar: coconut brings hardness and big lather, olive brings mildness and conditioning, castor stabilizes lather, and butters add hardness and creaminess.
Explanation
In the book's recipes, coconut oil (lauric and myristic acids) gives hardness, abundant bubbly lather and strong cleansing. It traces fast and can dry the skin at high levels unless superfatted. Olive oil (oleic acid) gives mildness, conditioning and a stable, creamy lather, but it traces slowly and needs a long cure. Castor oil (ricinoleic acid) stabilizes a dense, creamy lather at 2–5%; above 5–7% it makes the bar sticky and soft. Shea, mango and cocoa butters add hardness and creaminess.
A typical balanced bar in the book is roughly 28–30% coconut, 15–25% butters, 44–47% olive and 2–5% castor.
What to do
- Check a blend in a soap calculator before you make it.
- To change the result, change the oils, never the lye.
Source: The Big Book of Homemade Soap — Interpreting Soap Calculator Quality Values