Let’s start out with the inspiration behind this post – I LOVE my cure rack (the place where all of the new soaps are sitting around waiting to be ready to use)! Once a week I get to look at all of the soaps I’ve made in the past 4-6 weeks or so, measure, smell, fondle, and just adore each and every one of the bars I’ve set aside for the “cure rack”. (Yes, I said fondle… any soap maker will agree; we love our soaps a bit too much!)
But what exactly does curing mean, and why should you care? Knowledge helps you understand the products you use, and helps you determine if a soaper knows what they are making, and selling. So, let’s learn a little about the curing soap.
Saponification is the chemical reaction between fat and lye that makes soap. I started here because many people confuse cure time with saponification. They’re not the same thing.
When the fat and lye is fully saponified, you have soap. It’s safe to use—the lye is gone (transformed into soap!) and any remaining oils that are left in the bar help to nourish the skin or hair. But being saponified doesn’t mean you should use it just yet! Soap can be fully saponified, but not cured.
What is Curing Soap?
Curing soap means that the soap is left to age, mature, and well… dry out. Soap is made from three basic ingredients: Fats (oils), Lye (use to turn the oil into soap), and Liquid (used to dissolve the lye, and add other properties to the soap). Over time, the excess liquid in the soap evaporates, the bar hardens and becomes milder.
How long does it take to cure soap?
Many soap tutorials will tell you that “the soap needs to sit for 4-6 weeks before you can use it”. But cure times vary based on the amount of liquid used in the bar (this could be water, juices, milk, or even beer!), the oils used in the recipe, and any additives that are included in the batch.
- Bars with a high percentage of soft oils (like olive) will take longer to cure than bars made with a high percentage of hard oils (like coconut).
- Bars made with a higher percentage of liquids will take longer than soaps made with what soapers call a “water discount” (which means using less liquid in your recipe)
A typical cure time is 4-6 weeks, but what determines when a soap is “done”? The most reliable factor is weight. Each week, I weigh each soap on the cure rack. When the soap goes a full two weeks (most soapers wait one week) without changing weight, I know that it’s both safe to use, and will hold up when used. Let me explain…
Glycerin in Handmade Soap
A byproduct of soap making is glycerin, and the glycerin content of the soap is why the cure time is so important. Glycerin is a humectant—it attracts and retains the moisture in the air nearby via absorption, drawing the water vapor into the soap. Glycerin is great for skin but makes for one mushy bar of soap. As the bar cures, the water content evaporates, and glycerin in the soap is able to better withstand exposure to water (aka your shower).
When weighing my handmade soaps each week, I’m really weighing the water content in them. Once the weight stops changing, I know that the water in the soap is stable to the humidity of the air. You can read more about handmade soap, and why commercial soaps don’t have glycerin here.
Why an Extra Week?
Technically the soap is cured use is the weight is the same as last week, but I’ve always waited for a bar of soap to have two full weeks of the same weight before I call it cured. Maybe I just like having soaps on the cure rack, but either way, with that extra time, I know the soaps that make it into your hands are fully cured, and ready for your next shower before they hit the shop. Soaps, like a fine wine, get better with age – so some of my limited edition bars are left to cure for 3 or more months!
A Quick Myth Buster: Castile Soap
People say that castile soap (any soap made with 100% olive oil is Castile — and no Dr. Broner’s is NOT Castile, regardless of what the label says) take a full year to cure. My Castile soaps take about 6 weeks to fully cure as I use a water discount in the recipe. But they do continue to get milder and have an improved lather over time. I love a multi-year-old Castile. It’s rock hard, withstands being used multiple times a day, and has a very delicate and silky lather.