Curing is the process for which the soap bars finish saponification and dry completely. It takes about a month. Find out why your homemade cold process soap needs to cure and how to do it.
Previously in this Soap Making series: How Do You Make Cold Process Soap? or How to Make Soap by Melt and Pour
Why Does Your Homemade Soap Need to Cure?
Even if your soap seems to look good to go after unmoulding it, there are two main reasons why you need to cure freshly made soap. First, to allow saponification to complete. Second, to let the water content evaporate out and the bars to dry.
Saponification is the process where the oils in your recipe bond with the lye. This process is mainly complete in the first 48 hours after you make cold-process soap but the remaining 5% of lye needs more time.
Furthermore, the recipes in this website use enough water to give time to reach trace and work with the soap without your soap batter hardening too fast. That water is still in your bars when you take them out of the mold. If you don’t allow them to cure and dry then your bars will not last once you start using them: they will turn into a slushy mess in the bath or shower. Soft uncured soap will desintegrate quickly if you get it wet.
Even with water discount (=using less water in lye water) techniques that will speed up cure time, used by more experienced sopa makers, it’s still required to give soap time to dry.
Many websites and sources mention that with hot-process there is no need to give time to cure soap, because the temperatures and time during the cooking phase allow the saponification to fully complete. But the fact is that you need to cure soap whether you’re using the cold-process or hot-process method, even if with the latter the cure time is reduced. That’s because it’s just as much about letting the bars dry as it is about saponification.
Unmoulding And Cutting Soap
Even if you believe that the soap is good to pop out of your mold, you should leave it for 48 hours in the mold. This means that by the time you take it out, the vast majority of the soap batter has (most likely) gone through saponification. After two days it’s safer to handle and will be harder than it was the day before. I’ve almost ruined a couple of soaps with the rush to see how it looks.
For 100% olive oil soap, the best is to let it sit for 7 days, and use silicone molds with single soaps, avoiding the need to cut them. I am still to find out when to cut a loaf of olive oil soap, as the last bar I’ve made was very hard in the middle and creamy soft in the edges.
Still, my advice is to wear gloves for handling your bars at the point of unmoulding. It’s unlikely that you’ll feel anything uncomfortable but there could still be lye in the bars. Touching fresh soap that’s lye-heavy can cause skin dryness and irritation, especially if you have sensitive skin.
If you’ve used a loaf mold, slice your bars up. This will increase the surface area for drying and cutting fully cured loaves can be more difficult (loaf is too hard and can break when you cut it). The size you cut them is up to your personal preference.
Please, be careful as sometimes the loaf soap is soft in the edges, although it’s good to cut in its core.
To cut the soap into bars, you can simply use a knife but there’s a good chance of having uneven bars.
To have nice rectangular bars, the best way is to purchase a professional cutter. The bars will come out nice and even and you will be able to cut several bars in one go. If you want a cheaper cutter, use the ones with a wooden box or a wire cutter, all available at Ebay. Some sets also have the soap load mold – I’ve bought one of these and am happy with it.
Professional Soap Cutter
Wooden Cutter / Wire Cutter
If you’re handy with woodwork, you can make one yourself. There are dozens of videos on YouTube with DIY soap box cutter projects – like this video, for example. But this set is cheap enough and brings the loaf mold as well. You will definitely save time and money, compared with other apparently cheaper solutions.
How to Cure Soap
Once your bars are unmoulded and sliced, it’s now time to cure them. There are many places that you can cure your soap but, basically, it just needs an airy place out of direct sunlight. You can use a bookshelf, metal racks, cardboard boxes, stacked crates, or even make towers of soap. Stacking soap during curing is perfectly fine and if you live in a warm and arid place, you could even cure your soap outside. I prefer to keep it indoors in a metal rack like this:
Your soap won’t look wet but there will be moisture and it can react with surfaces. Line them with greaseproof or baking paper to protect both your soap and the units you’re using to cure it on/in. Then space your bars out so that there is plenty of airflow around them.
Even if you’ve only made one batch of soap, it’s always better to label it. Mark the date you set them on the shelf and also which soap it is. It could be a batch number or simply the recipe name.
If you have different batches, place them side by side but keep them from touching. If you’ve used different scents, they can affect each other during that long cure time (even if not touching). Also, the cure time begins not from the day you made the soap, but from the time you set it on the shelf.
Soap Curing Time
The time you leave your soap to cure is dependent on the oils and water content of your recipe. Four weeks is a good enough time for the majority of cold-process soap recipes. In hot process soap making, some of the water in the recipe will evaporate off in the cooking process. Not all though. That’s why hot process soap needs to be cured for 1-3 weeks.
Olive oil soap usually takes longer to set in the mold AND cure. It will make a harder, milder, and much better quality soap bar if you give it at least six weeks to cure — if not six months. Some soap recipes using salt take this time to cure, but they make extraordinary and marvelous soap bars. I am yet to make and try them.
Ways to cure handmade soap faster
There are a couple of tricks to shorten curing time of soap, although, I repeat, it always needs to cure for some weeks.
The first is to use the water discounting method, which means to use lye solutions with less water – bigger lye concentration. In a standard recipe, you use a 33% lye concentration. For example, if your recipe calls for 33g of lye then you’d make your lye solution with 33g of lye to 67g of water (33g is 33% of 100g). Bringing your lye solution to a 40% concentration can shorten your cure time to just two weeks.
Be aware that a lot of other problems might come up to increasing lye concentration, like soap batter seizing (instantly solidifying) or soap gel happening when you don’t want it, therefore, don’t use it on your own until you’re an experienced soap maker.
Another way to cure handmade soap faster is to use a dehumidifier or an electric fan. You can also cure your soaps outdoors if it’s warm and very dry. Make sure to keep them out of the sun and that they have really good airflow.
The time it takes the soap to cure will vary but if you weight a bar regularly and notice that it’s not losing weight then it’s probably ready. If you’re going to use this method it really helps to know the weight of a fully cured bar of soap. If you’re using the same batch and size as a previous batch weight one of those bars.
Hope you have enjoyed this article and found it useful! If you still have a question or want to make a suggestion, please leave a comment below.
Curing Melt and Pour Soap?
If you’re making the soap base at home, the curing time is around 2 to 3 weeks – I suppose the added ingredients accelerate the saponification process, pretty much as in hot process with temperature.
But when you’re melting the soap base to make the final soaps with fragrance, colorants, natural addictive and pretty shapes, the soap base is actually ready and doesn’t need to cure.