When you’re shopping with various soap makers you may hear terms like Cold Process and Hot Process. These are both valid methods of making soap by combining oils and lye and other additives. The biggest difference is that with Cold Process soapmaking complete saponification happens after molding the soap batter while with Hot Process the soap batter is “cooked” through the entire saponification process prior to molding. Ultimately, the soap is completely safe with no active lye left at the time of molding with Hot Process soapmaking and can be used immediately. There is a huge amount of misinformation regarding the “curing” of Cold Process vs Hot Process soaps. And I’ll give a little more about that to follow.
When I started my soapmaking journey over 25 years ago I started using the Cold Process method. I started experimenting with a crockpot method of the Hot Process method to completely cook through the chemical process and adding my additives AFTER the cook. While this did help keep me from dealing with seizing of my batch with new essential oils or fragrances……and it did prevent color morphing from the colorant going through the chemical process……and it did allow me to add my super-fat (additive of beneficial oils and butters) without it getting destroyed by the high heat of saponification….it did take away from the fluidity of the soap batter. What this means is that I was “glopping” the finished soap into the molds and there was literally no chance of beautiful swirls of color if I wanted.
Fast forward to about 8 years ago….I began High Temp Fluid Hot Process soapmaking. What this means is that I have continued to make soap using the Hot Process method. BUT, I do so in such a way that it is no longer so thick and dry that I have to glop it into the molds. It is as fluid as Cold Process and I have the ability to swirl colors and do nice looking soap tops if I choose. The soap is made with the oils and lye at high temperatures and this high temperature is sustained throughout the process of saponification. The heat speeds up this process. So my soap is cooked through and completely safe to use before it even goes into the mold to cure.
Now, about curing…..it is a huge bit of misinformation to assume that Hot Process soap does not have to cure. While yes, it is completely safe to use out of the pot, it is not recommended. The “cure” time is not necessarily for the process of saponification to complete but more for the soap to harden. By allowing the soap to cure for 4-6 weeks the extra water evaporates and the bar becomes harder. The cure will help create a bar of soap that will be longer lasting. If soap is not allowed to cure, regardless of method of manufacture, it will melt too quickly and become a gooey mess in your soap dish. The truth of the matter is that even with Cold Process soap the process of saponification is complete within 48 hours so the remaining cure time with Cold Process is also for evaporation and soap hardening. Curing also helps to create a milder bar of soap no matter what process is used.
This was just a simple and basic explanation of the process we use to make our soap. We are happy to go into more detail if someone requests.