Why does Castile soap take so long?
Short answer
Olive oil is mostly oleic acid, which saponifies slowly: slow trace, a soft young bar, and a 6–12 month cure.
Explanation
Young Castile has a slimy lather and a soft bar. It's safe to use after 4–6 weeks but not at its best. Given 6–12 months, it crystallizes into a hard, creamy, very mild bar. The book's recipe uses a water discount and chilled water to help, and blends in 20–30 second bursts with rests for 5–10 minutes.
What to do
- Plan Castile well ahead: a year of curing is even better than six months.
Source: The Big Book of Homemade Soap — Castile Soap: Testament of Patience & Purity