Category Archives: Definitions


I made a mistake in my soapmaking this past Saturday that I’m really looking forward to seeing how it turns out.

Bucket o’ mistake-soap.

Let me provide a bit of background. When I’m setting out to make several batches of SunSoap, I do a fair bit of prep work. I mix up a giant vat of the relevant oils and heat them together, and measure out lye in the appropriate quantities to make the assorted batch sizes to fit my various molds. Then for each individual batch I weigh out the right amount of the mixed oils, add the relevant lye allotment, and color/fragrance as desired.

Well, on Saturday I got a bit too caught up in what I was doing and measured out too much oil for one batch – basically, I measured out enough oil for a five-pound batch despite using a four-pound mold. This wouldn’t have been a significant error if I’d also grabbed a five-pound allotment of lye; I’d’ve had too much soap for the mold, but I could have put the extra somewhere else. But no; I used the four-pound allotment of lye, and didn’t realize the mistake until the soap was colored, fragranced, and poured into the mold. Which means this batch of soap is now about 30% superfatted instead of the desired 3% or so.

What is superfatting? It’s a technique used by many artisan soapmakers to provide an extra moisturizing bar of soap by including some excess in the oil phase which will remain unreacted with the lye and remain in the finished soap. Often, carefully-selected oils are added very late in the soapmaking process in an attempt to make these oils more likely to be among those unreacted with the lye and present a particular profile in the moisturizing aspect. I’m not 100% convinced that doing this actually does have any significant effect on which oils remain behind in the finished soap, but this doesn’t stop me from adding the avocado oil late in my soaping process. After all, it can’t hurt, right?

The technique of superfatting very likely arose not primarily as a means of making soap more moisturizing per se, and more as a way of allowing for inaccuracies of early soapmaking methods and ensuring that no lye remained unreacted in the finished soap. Without accurate scales – or, even earlier in soapmaking history, without lye of known strength – it was difficult to know one had added the correct amount of lye, and if it is virtually certain there will be unreacted ingredients in the finished product, it’s better and safer that they be oil rather than lye. Hence, superfatting. This is rarely a problem with modern methodology, but sufficient other benefits are forthcoming that a modest percentage of superfatting is almost universally used.

It’s not a technique without shortcomings, however. Highly superfatted soap doesn’t lather as well. Also, if too much excess oil is used, it can create large enough deposits in the soap that it can oxidize and create what is known in the trade as the Dreaded Orange Spots. This is not the necessarily kiss of death for soap, but it is rather unsightly, and in extreme cases the afflicted soap can actually go rancid. Yuck! So I try to keep my superfatting percentages below 5%, as a compromise between moisturizing and lather, and to stay well below the DOS threshold.

So what does this mean for my accidental 30% superfatted soap? Well, obviously it won’t be leaving my hands; if ever a soap were likely to go off in interesting ways, this would be it, and I don’t want that to happen out in the wild. But I’m fascinated to watch how it behaves, once it cures a bit. Will it be too soft to hold a bar shape? Will it lather at all, or just sort of sit there greasily? Will it develop Dreaded Orange Spots within the month? I have no idea! But despite dumping the batch out of the mold and replacing it there with a properly-made batch, I kept this around in a plastic box to let it progress as it will. For Science!, don’tyaknow. If I learn anything remotely interesting, I’ll let you know.

Curing Soap

What do we mean when we talk about letting soap “cure”? It’s a term of art, to be sure, and can be a bit less than fully obvious in meaning, even when the immediate sense is made clear.

Freshly made cold process soap is about 20% water, which makes it very soft. Within a day or three of first being made, it is safe to use, in the sense that the lye has essentially all reacted with with the oils and the new soap is no longer caustic.  However, it’s not really very good soap yet. It’s soft enough to be difficult to use properly, and not only that, due to it already being partially dissolved in its own water, it gets used up much more quickly than it would if it were let alone for a while before using. High-quality soap is soap with most of the water gone from it.

So why do we call it “curing”? Wouldn’t “drying” work as well? Sort of; it’s not drying in the sense of drying dishes, after all. You can’t wipe it off or point a hair-dryer at it and get it done faster, as it’s already dry on the surface and the hair-dryer will mostly just melt the soap and make a mess. It’s more like drying in the sense of drying meat or fruit; exposing to dry air (and sometimes gentle heat) until enough of the moisture from inside the meat, fruit, or soap has diffused out toward the surface and evaporated away, leaving beef jerky, raisins, or properly-cured soap!

Part of the current curing rack load.

Having established the value of curing soap before using it, how does one go about the process? Well, soap will mostly cure by itself in a few weeks if left in a place where air can circulate around it well enough. In my soap room I have several screen-lined shelves as well as a selection of baker’s racks, which I arrange just-sliced soap on and leave them for a while. I try to accelerate the process by dehumidifying the room and keeping it a bit on the warm side, and sometimes the soap is fully cured and hardened in as little as two weeks, but when possible I try to keep it on the racks for four.  In some cases a soap will turn out to need extra curing for some reason, so it stays on the shelves even longer. Soap never goes on sale until I’m satisfied it’s hard enough to be an easy to use, long-lasting bar.

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!