Curing Soap - Misconceptions and Mis-information!

I see a lot of misinformation, confusion and half-truths circulating when it comes to why we cure soap. I want to touch base on what saponification is, the curing process, and why you should wait to use and sell your soaps! This is true for ALL cold processed AND hot processed soaps.

What is Saponification?

One thing I hear is people asking regularly if they can speed up the process of curing. No, you really cannot. Here is what happens after you pour your soap into a mold. For the first 24-72 hours the soap goes through saponification. This is a chemical process where the sodium hydroxide solution combines with the oils and butters and creates a new compound, an alkali salt of a fatty acid.

Once the saponification process is complete, usually in 24-72 hours, the soap is safe to touch. There is no longer any sodium hydroxide left. This however, does not mean you “should” use the soap, although you “can”. You may find at this stage the soap is harsh and may be more stripping to your natural oils on your skin than it will be in a few weeks or months. You need to let your soap cure. The cure time is not set in stone, and will be affected by the ingredients in your soap recipe, the amount of water/liquid used, and the humidity of the environment.

What is curing?

You may hear many, many soap makers tell you the curing process is meant to let the water evaporate from your soap to make a harder, longer lasting bar. While that is true, that is not the whole answer. There is significantly more happening inside your bar of soap than just the evaporation of liquids used in the process to make the soap.

At this point, I want to debunk two myths. The first myth is that cold process (CP) soap takes weeks after it is made to become safe enough to use or sell. The second myth is that hot process (HP) soap is ready to use and sell right after it is made.

Hot processed soap is “cooked”, meaning that once you are done that stage, the soap is fully saponified in a few hours. It is true that cold processed soap does take longer to saponify, a day or two. This means once both soaps are done saponifying they are “safe” to use o the skin, but neither so will be “best used” at this stage.

The stages of the curing process

Loss of water

Evaporation causes your bars to shrink, lose weight, get harder, and be less soluble in water. You can track the weight loss to determine when your bar is ready for use by weighing it every few days and tracking the change. One interesting thing to note is that because hot processed soap typically used more water, it will actually take LONGER to dry (cure) than cold processed soap.

Developing a crystalline structure

After saponification, when you allow your soap to cure, you are allowing the crystalline structure within the soap to form and tighten. The bar will get harder, become milder, and last longer. You may even notice a better lather after you let your bars cure properly.

This is something you cannot see or measure, which is why many soap makers either ignore it, don’t think it’s important, or just don’t know! Since I am not a chemist, and I don’t have a science background, I had to research this to wrap my head around what is going on, inside my bar of soap.

I will admit that finding scientific papers and legitimate research out there on the soap curing process is not that easy to find. Sorry to the crunchy mom bloggers. I’m not saying they don’t provide valid information or talking points, but if you are reading this is encourage you to go further in your research and explore the science, don’t just believe what I tell you, or anyone else for that matter!

A bar of soap is made up of solid crystals surrounded by a film of liquid. The liquid surrounding the crystals is a combination of water, glycerin, and other water-soluble chemicals. A single molecule of soap is a fatty acid combined with a sodium ion. The sodium is from the sodium hydroxide we discussed earlier and the fatty acid comes from the fats we used. I’m not going to get down and dirty into the individual fatty acids that make up a bar of soap, as they will vary based on the different oils and butters you used in your recipe, and is the topic of another very lengthy, and probably multiple blog posts in the future!

Basically, a combination of myristic, lauric, palmitic, stearic, and oleic soap molecules in different sizes and shapes are jammed into a soap crystal, which has an outer later of liquid in the form of water, glycerin and other water-soluble chemicals. These crystals are jammed together and form a bar of soap.

At 4-8 weeks, most soap lathers better, lasts longer, and is milder to the skin. The water content has dropped, and the glycerin and other water soluble chemicals will be more concentrated. At this point the soap is usually ready to use and will no longer continue to reduce in weight (lose water). So then, why does a soap continue to “get better with time” if the curing process is done once the water is evaporated?

As the glycerin and other dissolved chemicals in the liquid phase inside your soap become sufficiently concentrated, the stearic and palmitics in the liquid phase will form solid soap crystals. These soap molecules also gradually trade places with lauric, myristic, and oleics in existing crystals.

The term for this is “salt out”. This is the process in which the soap molecules transform from a liquid state into solid soap crystals. Over time the crystals in a bar of soap will contain more and more less-soluble properties. I am glossing over some of the more technical science here as it can be overwhelming. I just want you to understand that curing is a complex chemical process, and not just waiting for your soap to lose its water content. Am I repeating myself? Possibly.

So, if you’ve made it this far, the gist of it is, the concentration of the different fatty acid properties in the soap change over time. The bar of soap will contain more stearic and palmitic properties in the crystals, and more lauric, myristic and oleic properties in the liquid part of the soap. It is worth noting this is a slow process that can take months for a noticeable difference.

Clear as mud? Good thing you have all that soap!

Conclusion

The curing process is more than just waiting for your bars to get harder and lose their water content, there is a complex, chemical change happening in the bar, the crystalline structure is changing, and the longer you wait, the better your soap will perform.

For me, I am happy with my recipes to use them after 6 weeks. This is a hotly debated topic in the soaping world, and at the end of the day every soap maker will make their own decision. I just want each of us to be armed with as much information as possible to make informed decisions.

If you have comments, questions or concerns, I would love to hear them. We are all still learning and growing, no matter how long we have been making or using a product!