Castile soap

Castile soap is traditionally a cold process soap made from a very high percentage, often close to all, olive oil. The name comes from the Castile region of Spain, where this style of soap originated, and it is prized for being mild and gentle compared to bars made with a wider mix of oils.

A pure or near-pure olive oil recipe behaves differently from a multi-oil recipe: it typically takes noticeably longer to reach trace, and the finished bar needs a longer cure, often several months rather than the usual four to six weeks, to become firm and long-lasting rather than soft and slow to harden in the shower.

Because it can seem slow or unpromising in the days after pouring, a common mistake is assuming a castile batch has failed and reworking it too early, when it simply needs more time on the curing rack than a typical multi-oil recipe.