Curing handmade soap is a crucial step in soapmaking that ensures your handmade bars are at their best. However, if you get a group of soap makers together and ask them how to cure soap, you’re bound to hear different opinions about how long soap needs to be cured, criticism if you don’t cure as long as they do, and, well… it can be a pretty hot topic of debate! So, let’s talk about it and discuss the facts about curing soap.
Saponification vs. Curing vs. Aging
First, let’s define a few terms that are often confuse the cure time debate:
- Saponification is the chemical reaction where oils and lye transform into soap. In cold process soap, this happens in the mold over a few days. For hot process soap, saponification is complete by the time you mold it, allowing immediate use (as in your soap is safe to use, but it will for sure be mushy on the soap dish!)
- Curing handmade soap refers to the process of allowing soap to dry and harden over time. This period allows excess water to evaporate, resulting in a harder, longer-lasting bar. Scientific Soapmaking, by Kevin Dunn, emphasizes that curing is primarily about reducing water weight, not altering the soap’s chemical composition. The process takes “about” 4 to 6 weeks and is essential for both cold and hot process soaps.
- Aging is often confused with curing, but it refers to the soap’s overall maturation beyond the initial cure period. While not necessary, some soap makers believe aging further enhances the soap’s qualities.
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Why Handmade Soap Needs to Cure
Curing handmade soap improves the quality of both cold process and hot process soaps in several ways. It enhances the soap’s hardness, which means it will last longer when used. It also helps in developing a richer lather and ensures the soap is gentle on the skin. Without proper curing, soap can be soft, dissolve quickly, and may not perform as expected.
Note: melt and pour soaps do not need a cure time. Melt and pour soap is soap that is already made and ready to use (you can just slice off a bit of the block and hop in the bath).
And I would like to point out one more time that BOTH hot and cold process soaps need to cure for optimal performance. Some uninformed soap makers believe hot process soaps don’t need curing. While HP soaps can be used right away due to completed saponification, they still benefit from curing to evaporate excess water.
Where to Cure Handmade Soap (aka The Cure Rack)
Cure your soap in a cool, dry place with good air circulation. An open rack is ideal as it allows air to flow around the bars, promoting even drying. It’s a simple as that! Here are a few things to avoid and some additional tips for you too:
- Avoid closed containers, which can trap moisture, slow down curing, and even lead to DOS (from the trapped moisture).
- Use a curing rack or tray that is plastic or stainless steel. Curing on aluminum racks will result in DOS on your soap. I do use a metal rack, but the soaps do not come in contact with it. I keep them on my handy cafeteria trays.
- Do not line your curing racks with aluminum foil! If you must line your racks, use paper. Good old compostable kraft paper is just fine, as is a sheet of cardboard or paperboard. Just no metals.
- If you live in a humid environment, consider a dehumidifier for your soap room. It will help with the curing process and help prevent DOS on your soaps.
- You don’t need to have a fan blowing on your soaps.
- You don’t need to turn your bars.
- You don’t need to weight your soaps every week if it’s a soap you’ve made before (more on this below).
How long does curing handmade soap take?
If only I had a one size fits all answer for you my soap friends! The answer, though, is… it depends.
It depends on the water content of your recipe. It depends on the humidity level in your soap room. It depends on the size of your bar. It depends on how much air flow the bars are exposed to…. it just depends.
However, “typically”, soap should cure for 4 to 6 weeks. This is the general time frame that allows enough water to evaporate, ensuring the soap is hard and long-lasting. Here are a few examples of varying cure times to help illustrate:
- Typically, my soaps cure in about 2-3 weeks. This is using a 1:1 lye solution with my go-to vegan palm free recipe. If I add more water, then I typically need to add 7-10 days to the cure time.
- My coconut-free soaps cure in 3-4 weeks. That’s with a 1.5:1 lye solution. BUT, these soaps are MUCH better if aged for 3 months.
- My shampoo bars cure in about 5-6 weeks.
- Rebatched soaps cure in anywhere from 4-10 weeks, depending on the process used, how much water was introduced, and how big (or small) I cut the bars.
Does using less water make soap cure faster?
One of the biggest factors affecting cure time is simply how much water you start with.
In 2026, I ran a controlled soapmaking experiment using the same base formula with two different water amounts: a 1:1 water-to-sodium-hydroxide ratio and a 2:1 ratio. I weighed the soaps repeatedly as they cured so I could see when they reached what I consider practical weight stability — the point where meaningful water loss has essentially stopped.
The low-water soaps reached practical weight stability at about 3 weeks, while the higher-water soaps generally took about 5 weeks.
So in this experiment, using less water shortened the time it took the soaps to reach stable weight by approximately two weeks.
That does not mean every 1:1 soap will always be cured in three weeks. Bar size, recipe, airflow, humidity, temperature, and other process variables can all affect cure time. These were small test bars, so I would not use these numbers as a universal cure schedule.
But the overall pattern was very clear: more starting water meant more water had to evaporate during cure, and the soaps took longer to reach a stable weight.
We also saw some intriguing clues that hotter process conditions may move some of that water loss earlier in the process, but that was not isolated well enough in this experiment to call it a firm conclusion.
If you want to see the full experiment, including the water comparisons, temperature variables, cure-weight charts, and our long-term DOS observations, you can find it inside Myth Busting — Water and Temperature with Cold Process Soap.
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How do you know when a bar of soap is cured?
It’s all about water weight! Once the bar stops losing weight (from water evaporation), then it’s cured. Really, it’s a simple as that. In the Ultimate Natural Soapmaking Course I provide a cure log for you to download, or you can just a scrap piece of paper like I used to do. Either way, here’s how to track the cure time for a new soap:
- Weigh a bar of your freshly cut soap. It’s best to weigh it in grams as we will be recording small changes in weight over the cure time.
- Each week, weigh the bar again. Recording the new weight each time. You can notice changes from .5 to 1 grams in weight.
- Eventually, the soap will stop losing weight. That is when all of the excess water has finally evaporated. At this point, your soap is considered “cured”.
Assuming nothing changes in your recipe, and your curing environment has a stable relative humidity, this recipe will have the same cure time each time you make it.
And there you have it! You’re all set to cure your soaps, and maybe even contribute to a soapy debate on curing 😉 If you have any questions or other tips to share about curing soaps, drop a comment below!
Until next time, happy soaping!
p.s. Here’s a pic of one shelf of my cure rack with a few custom orders on it.
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