Like firewood, as the soap cures, most of the water used in the recipe evaporates out of it. Cured soap is harder, milder, and more "finished."
How long to cure it?
There are really two purposes to cure:
- To make sure that the saponification process is completely complete. This generally takes about 24-48 hours. Yes...I know it sounds like blasphemy...but your soap really IS safe to use after a couple of days.
Now...before you all yell at me...it does become milder as it ages and cures more...but only a TINY TINY bit. 99% of the ph changes happen in the first 48 hours.
- The real reason to cure your soap is for the water to evaporate. A harder bar of soap will last longer, lather better and just be overall better soap. For this, yes, wait a few weeks.
BUT, it really is only safe if you are an EXPERIENCED soap maker though...it is NOT for beginners. Here's a good article about it. Making Soap with a Water Discount