Soap FAQ – Curing, Sweating, and Seizing

soap and oil bottles and wood table 151x151Here are discussions of three terms related to soapmaking that don’t come up as often as we think they would. For the first term – Curing – the discussions is is mostly informational. For the second – Sweating – it addresses something that can concern soapmakers, but is in the end harmlessly natural. For the third term – Seizing – the discussion points out something potentially more serious, something that can sneak up on you.

Two Things at Once
Curing is a process involved in all kinds of products, most commonly meat and fish. Officially, it’s a process during which a chemical reaction or physical action takes place, resulting in a harder, tougher, more stable substance or bond.

Laboratory.For meat and fish, curing is a form of preserving. For cold-processed soap, it’s more a form of finishing. For the 4-6 weeks it takes cold-processed soap to cure, there’s a slight bit of pH finalizing, but mostly, curing consists of a physical action – evaporation – during which the bar becomes harder as it loses water. Soap can be used before it’s fully cured, but since it’s not really finished, and therefore not as hard as it will be, non-cured soap won’t last anywhere near as long as bars that are allowed to finish.

It’s in the Chemistry
Soap doesn’t really sweat. In fact, what happens is the opposite of sweating. But it can look like it sweats. And that sweating can take the appearance of “weeping” or the formation of a crystalline-like powder or haze. One source we found uses the term “glycerin dew.”

Natural Handmade Soap. SpaThe truth lies, as much does in much soapmaking, in the chemistry. One of the natural byproducts of true soapmaking is glycerin. In that respect, all true soap is glycerin soap, just not in the way that term is commonly used. Glycerin qualifies as a humectant, a substance that attracts and retains moisture beneath the surface through absorption. Natural soap, with its glycerin retained, can attract humidity due to climate or where it’s stored. Especially in humid climates, sweating can be an issue. The best advice is the simplest: Let your soap harden and cure at natural room temperature and then store in a cool, dry place.

Trace Acceleration and Seize
Aleppo SoapSometimes chemistry can happen too fast. With soap, too fast takes the shape of “trace acceleration” where the speed of thickening overwhelms the process of saponification. Instead of a naturally thickening mix, you get batter too thick to pour, or worse, you experience true seize and you wind up with a hard, unusable mass.

You’re right to think this is something to avoid. The main culprits are fragrance oils and alcohol. Both have been known to cause trace acceleration. If you’re making organic soap and using essential oils, neither of those should be a problem. A third possible cause is the original temperature of your lye and oils. A prudent, commonly recommended  range is 80-100 degrees. With the possibility of other factors, prudence in chemistry is wise, especially given the consequences of haste.

3 thoughts on “Soap FAQ – Curing, Sweating, and Seizing

  1. Just this morning I was going to search why my 48 H soap, when taking it out of the mold, was so wet, and burned my hands a bit. Wondering what was the cause, I opened my unread email first, and Voila! Your blog post was right there! AHH, timely, as usual! So, is it the type of mold, or an ingredient, or just one of those random things? Last time, it was an almond milk soap; this time, calendula infused olive oil. Everything else was basically usual. I AM in the overly humid south…… Pulled it out of the acrylic pasta cylinder (now repurposed), left it wrapped up in parchment paper, and on the shelf to dry more (that wetness is Alive!). Perhaps, as you said above, in the south, I can expect this more.
    So addicted, shelley

    • Hi, Shelley. I’m not entirely familiar with 48-hour soap, and since it’s science, soapmaking can be affected by one of any number of variables. The fact that it burned your hands a bit, though, leads to me think it was lye that burned you. I’m guessing you didn’t get the oil-lye proportions wrong, so I’d look at how or why saponification wasn’t complete. Doesn’t sound like you’re using tricky ingredients, but it’s tempting to point to the differing soap base as the culprit. Is 48-hour soap hot-processed?

      • No, cp, I just meant it had sat for 48 h after making befor I tried to unmold it. I have been using the soapcalc.net to get my lye and water amounts. I figure out the percentages of each oil on recipes, then transfer the percentages to the mold size I’m going to use (boxes etc, all different), calculating how many pounds my particular box will hold (total oils x .39, then soap calc to add water plus NaOH devised by 16)…..Oy. Anyway, soap calc is what I use. This has happened twice. I’m in a quandary. Figured it was lye water, but does quit burning after flushing with water. Do you think I’m not mixing it long enough. I’m so concerned about seizing that I pour it at light trace. First batch was almond milk and honey. Second time was calendula infused olive oil with a little castor oil, only 8%. So, back to saponification….. Perhaps the high humidity here in Birmingham? Or else I just don’t mix long enough? Thanks, y’all!

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