Used cooking oil from a single restaurant in Niyodogawa became the starting point for PEA Soap. Here's how it works — and why zero-waste soap is harder than it sounds.
The first batch of PEA Soap came from oil collected at a small ramen restaurant on the main road. About eight litres — mostly rapeseed, some sesame, a little soy. Not the easiest oil profile to work with, but that's the point: we use what's available.
Cold-process saponification is the method. You combine the oil with a lye solution, mix until it traces — the moment the mixture thickens enough to hold a surface pattern — then pour it into moulds and leave it to cure for four to six weeks. The chemistry is simple. The variation is everything.
Used oils are unpredictable. The fatty acid profile changes depending on what was cooked in them and for how long. This means each batch of PEA Soap behaves a little differently — different hardness, different lather quality, slightly different colour. We test every batch before it goes out.
We've been asked why we don't just use virgin oil. It would be more consistent. The answer is in the name: zero waste is the constraint, not a side effect. The soap is good because we made it work within that constraint, not in spite of it.
Current scent: unscented, with an option for yuzu peel infused in the oil. Both are available while stock lasts.