Gel Phase

Next up in our series of terms to define: Gel phase! You hear soapmakers throw this one around a lot, and there are heated debates about whether it’s a good thing for soap or not. I come down on the pro-gel-phase side, and do my best to make sure all my batches go through it – so I’ll break it down a bit here and explain what some of the hype is about.

Most soapers these days use the “cold process”, which means that, unlike the stories my grandfather used to tell when the women of his family would stand around a cauldron in the yard on hog-slaughtering day and cook up a giant vat of soap over a fire (in what I can only imagine was a long, hot, and horrifically stinky process), we don’t add any heat at all to the reaction after we’ve mixed the lye and oils, or at most a very gentle warming, as from a heating pad. But as anyone who remembers high school chemistry knows, chemical reactions go faster in warmer temperatures, right?

Right. In fact, some of them even require heat as an energy input, which is why liquid soap has to be cooked – potassium hydroxide, the alkali used in liquid soap (more about this another time) reacts less readily with the oils than sodium hydroxide, and needs the heat to move it along. The reaction of sodium hydroxide with oils, though, actually produces heat, and with a sufficiently cunning use of blankets or other insulation, we can trap some of that heat and heat up the mold filled with soap, which accelerates the reaction, which produces still more heat – in a positive feedback loop that takes the temperature of the soap in the mold from around 100-120 degrees F when poured to, ideally, around 200 degrees F, and speeds the saponification process up significantly. The hot end of this is called “gel phase”, because when the proto-soap gets hot enough, it goes glass-like and translucent – it becomes, in fact, a gel.

This is what it looks like just after pouring into the mold…

…and here it’s in the middle of gel phase.

Gel phase does more than just speed up the process of turning oil+lye into soap. It also changes the texture and consistency of the finished soap. Now, soapers who prefer to avoid gel phase are still making soap! It takes a bit longer to finish saponifying, and the curing times are longer, but there are plenty of people who choose to make soap that way because they like the appearance better.

But faster isn’t always better, either. If the initial temperatures were too high, or the insulation is too thick relative to the ambient temperature, or there’s something about the fragrance or the ingredients in the soap that accelerates the process (honey, beeswax, and fragrances with spice notes are common culprits here), the positive feedback loop mentioned above can hit a sort of runaway process, and create what is semi-affectionately known as a Soap Volcano. This happens when the temperature gets high enough that the water in the proto-soap starts to boil, and the soap it’s embedded in is forced up and out of the mold – sometimes in a flow, sometimes in an explosion, but always in a mess. So watch your temperatures, and check your soap an hour or so after you put it to bed to make sure it’s not going CRAZY on you!

There are five batches of soap under that pile of blankets, which I’ve now unwrapped and looked at three times. I think they’re safe to leave for the night, by this point!


About Amy Young

Founder of Foam on the Range soaps. View all posts by Amy Young

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