Sugar's Soap Science Corner
Since I love the soapmaking process so much, I decided to nerd out and share some tidbits about that process with you, in no particular order:
Tidbit #1: Curing
Sugar Bee Bath soaps cure for a minimum of 10 weeks before they are announced for sale. There are three objectives in curing: Saponification, evaporation, and crystallization.
While the saponification process is usually complete within 48 hours after mixing the oils with lye water (PS: NO LYE IS LEFT IN THE SOAP), it is only about 99% complete once it is unmolded to cut. Leaving it to cure after it's been cut allows for the process to complete. Technically, this shouldn't take very long. However, a main ingredient of soap is H20. By the time it is unmolded and cut, the soap may be perfectly safe to use, but it is often quite soft and would likely wash away within days if you were to use it at that point. That is why the evaporation part of the curing process is very important.
Once cut, each bar is placed on a sheet of freezer paper to cure longer. I will periodically go and move the bars around on their sides so that all sides are exposed and therefore allowed to cure (while admiring the smell and the swirls in it each time). Depending on how much water is initially used, a bar may shrink in weight by as much as 50-75 gm as it cures.
But, like a good wine, the longer you let your soaps "age", the better they will be. This is because of the crystallization process. Soap is basically just a mixture of various acids (from the oils) and salt (sodium hydroxide) which bond to form a crystal-like structure. On a microscopic level, true soap will look like a bunch of crystals surrounded by liquid. That liquid is usually composed of water and glycerin, and the crystals are saponified acids, each with its own unique molecular structure. Both my Cold Splash and Sage & Cedarwood soaps were left to cure in a relatively cool area, and as a result you can see some of the crystallization in them.
There's a lot of science I'm going to leave out here because it gets pretty technical, but the gist of it is: when you wash with soap, the crystals move around and abrade each other, and that gives you a lather. In 'young' soap, the composition is loose because the liquid surrounding it contains more water. That results in less lather, and a bar that doesn't last very long. As the water evaporates, the space between the crystals lessens, and the soap becomes harder, giving you an amazing lather. The more you rub the soap on your skin, the more lather you will get. (Source: https://classicbells.com/soap/cure.asp)
I recently found some bars I had made over six years ago in the bottom of a box I forgot to unpack when we first moved. I will tell you right now: they didn't look pretty. They were kind of yellow due to age and the scent has disappeared. But...wow. I have never experienced such an extravagant lather in my life! I honestly didn't want to leave the shower. They also lasted an extremely long time in the shower, where we keep the soap dry so that it doesn't wash away or get all gooey when not in use.
So to sum up: curing is a very important part of the process, and the longer the soap is left to cure, the harder/better it will be.