Continuing the series of demystifying a soapmaker’s vocabulary, this post will deal with the issue of “trace”, a term we toss around casually but which refers to a very important transition point in the making of soap.
As mentioned in the last definition-post, the first milestone when blending oils and lye in soapmaking is to reach an emulsion – but these two substances would not create a stable emulsion were it not for the chemical reaction that begins the instant the lye hits the oil, converting these components into soap.
To that end, after emulsion is achieved, we carry on stirring the mixture. This continues to blend the components together and keeps them in constant motion, which has two effects: First, further mixing of the oils and lye keeps the emulsion from breaking apart immediately. Second, vigorous stirring helps accelerate the saponification (that term’s coming up later!) reaction by increasing the motion of the particles involved – similar to the way salt dissolves much more quickly when you stir it than when you just dump it in water and leave it to sit.
So, as stirring continues, the oils and lye are turning to soap right before our eyes, and at some point this reaches a state from which the emulsion of unreacted oils and lye will no longer break apart, being now held in suspension by the dissolved soap. While this is the chemically significant event we’re waiting for, we can’t see fatty acid molecules and sodium ions; all we can see is a sort of creamy off-white liquid that we’ve been stirring for a while now. And as most soapmakers don’t have sophisticated machinery to monitor the rapidly-falling pH in real time, or other mechanisms that would tell us what’s going on in there, we need another cue to use to recognize this point – much like my great-aunt was always able to pick out the right moment to stop cooking her peanut brittle by look, smell, and sometimes a glass of ice water for extra verification.
Wait a minute. Why do we care so much about this exact moment in the road to soap? Well, there are a couple of reasons. First, it means we can stop stirring all the time, which for people trying to make soap without immersion blenders or other appliance-assisted stirring is a cause for a tremendous sigh of relief. Second, once this happens, the amount of time in which one will be able to stir the soap is rapidly coming to a close, so if we want to do pretty things with colors, or indeed sometimes even get it into the molds without feeling like we need to resort to a putty knife, it’s important to recognize the early signs of trace so we know when to start working fast.
So, how is it we tell? Early/light trace not always immediately apparent until you’ve made a few dozen batches, but middle/late trace is unmistakable: The proto-soap begins to behave more like pudding than like cream, and the trails (or “traces”) left behind your spoon as you move it through the pot become quite obvious. Depending on recipe, temperature, and fragrance oils, this stage might last for long enough to do elaborate swirls/pours/fun things with six colors and some glitter, or if you’re really unlucky it might last less than a second on your way to a pot of seized soap. But it always happens, and learning to recognize it early was probably the first accomplishment in my soaping career that I found really, deeply satisfying in the way things only are if they take a while to click.
And that’s what we mean by “trace”.
P.S. I’ve never managed to get a photo of the middle phase of trace; it seems I’m always busy doing things when the soap hits that phase. If I ever do manage to get a good shot of it, I’ll add it to the post later.