Do Handmade Soaps Need to Cure?
Handmade soaps need to cure for approximately six weeks in a low-humidity environment with good air circulation and minimal exposure to sunlight.
Two of the main benefits of curing handmade soap: gentler soap and better lather. As the soap ages, it becomes milder and the lather becomes more abundant.
Also, curing makes handmade soap harder, slower to dissolve in the shower and less likely to suffer damage during shipping or transportation. After cutting the soap into bars, it is placed in a dry, well-ventilated area so that water can evaporate out of the bars. Curing handmade soaps takes a minimum of four weeks, but 6-8 weeks makes the soap even harder.
During the first few days of curing, the soap is too harsh to use. This is because the lye is still reacting with the oils to form soap. This chemical reaction can be sped up by cooking the soap on the stove or in a crockpot, but since some of the water evaporates during cooking, the resulting soap is very thick and more difficult to work with, making a more rustic-looking bar. The method of cooking the soap is called “hot-processed” and the method that I use of letting the reaction occur at its own pace is called “cold-processed.” Both processes of soapmaking benefit from a cure time of at least several weeks.
There's also another quicker method of soapmaking that I sometimes use when someone needs soap very quickly. It involves taking a special pre-made soap base that has already been cured and slowly melting it. Because this special soap contains extra glycerin, it can be scented, colored and poured into a mold with ease. Some people refer to this method as melt-and-pour, others simply call them glycerin soaps due to the additional glycerin. These soaps need to be fully wrapped in plastic wrap since the extra glycerin attracts moisture from the air and causes the soap to look like it is sweating.
One thing to note with cold-processed soap is that the scent will smell a bit different than in glycerin soaps. This is due to the natural chemical reaction (called saponification) taking place to turn the oils into soap. Fragrances made for cold-processed soap smell better after saponification, but tend to smell a bit chemically in melt-and-pour soaps. Fragrances made for melt-and-pour soaps can smell too light in cold-processed or even disappear completely.
What soapmaking method is the best?
If you want a fancy swirl or cool design, cold-processed is the best. But you'll have to wait 4-6 weeks for the soap to finish curing.
If you want a solid colored soap in an intricate mold, melt-and-pour is the best. But you'll have to live with the soap being fully wrapped in plastic until it's ready to use. Also, melt and pour soaps have been pre-cured, so the turnaround time is much faster.
While some argue that hot-process handmade soaps do not need to cure for more than 2 weeks, the additional water required for this method takes longer to evaporate, which basically cancels out the benefit of "cooking" the soap to speed up saponification.
While I have made soap using all three methods: hot-processed, cold-processed, and melt-and-pour, I generally stick to cold-process because of its flexibility with various designs. Swirls look very different in each type of soap because the fluidity of the soap is different at the pouring stage. Also, some natural additives, like goat milk or beer, need to be added before saponification so that they will not spoil in the soap.
When I share soaps on Facebook or add listings to my site, I generally wait until the soaps are fully cured to share them, partly because I don't want to damage the softer soaps by the extra handling required to photograph them. Lately, though, I have considered adding a section to my site called “On the Curing Rack.” If that's something you'd enjoy seeing, let me know in the comments!