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Troubleshooting: Crackling & Glycerin Rivers in Soap

Beer Soap with Crackling Effect of Glycerin RIvers
Beer Soap with Crackling Effect of Glycerin RIvers

In the Modern Soapmaking Troubleshooting series, we explore various soap making problems and find out what went wrong plus share some tips and tricks to put the smack down on issues that pop up.

Today we’re talking about…

Crackling and Glycerin Rivers in Soap

What is crackling and glycerin rivers in soap? The crackling effect found in some soaps is created by overheating or uneven cooling during saponification, as well as some colorants, and is often referred to as glycerin rivers.

Glycerin is a natural by-product of saponification, the chemical reaction that creates soap. Normally, the glycerin is dispersed throughout a bar, however, in the case of glycerin rivers, it collects together and creates this visual effect.

If the glycerin rivers are large enough, the soap will feel more pliable or softer in those areas.

What causes the problem? Glycerin rivers in soap is often caused by overheating/uneven cooling, and can be encouraged by certain colorants, like titanium dioxide (you may have heard of titanium dioxide crackles!).

Glycerin Rivers in Soap Colored with Pigments
Glycerin Rivers in Soap Colored with Pigments

These common soap making additives can increase your chances of seeing glycerin rivers:

  • Liquids with high sugars (milks, beers, fruit juices, etc.)
  • Pigments (oxides, ultramarines, etc.)
  • Fragrances that can cause overheating (florals, spices, etc.)

How do I prevent crackling? If crackling and glycerin rivers are common in your soaps, try to:

  • Ensure your colorants and additives are well mixed.
  • Reduce your soap making temperature, especially when using additives that tend to raise the overall temperature during saponification.
  • Elevate your soap mold to maintain a large amount of air flow to cool the soap down, or try using a soap mold that insulates less (wood molds insulate far more than other types.)
Glycerin RIvers in Soap Colored with Indigo
Glycerin RIvers in Soap Colored with Indigo

Is the soap usable? Crackling and glycerin rivers are an aesthetic problem, and do not affect the final soap’s safety or use. If the glycerin rivers are large enough, it can cause the bar to wear down unevenly during usage.

Can the soap be fixed? Since crackling and glycerin rivers in soap are a visual problem, and not a functional issue, it is not necessary to fix.

However, if you want to attempt to fix the appearance, you can always rebatch! In most cases, it is not worth the effort!

Remember, soapmakers are always their own worst critics. Most (non-soapmaking) people think the effect is unique and cool!

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13 Responses

      1. Oh thanks Kenna…I was wondering why i was getting them. I guess it’s because i gel my soaps and it’s already humid where i live… i will try less insulation and see if that helps.
        Great Job on the website! Was looking forward to it! Keep up the great work!

  1. I have been looking forward to your sites grand opening…..I will be visiting a lot and I also love glycerin rivers!

  2. I ALWAYS get glycerin rivers…..regular soap, milk soap, beer soap, you name it, I get rivers! Sometimes they look cool, and it doesn’t bother me, but you know when you have this perfect design in mind? Then wammo! Glycerin rivers! I like to at least gel my soaps, but prefer cpop. I saw recently on facebook that they can also be attributed to using “full” water, and that water discounting helps. Your opinion on that? I *always* use full water, discounting scares me, since it seems like I won’t have enough time to do my design! I see soapers that make a 1 to 1 lye water ratio, and to me, that seems way scary! I’ve been making soap for almost 6 years, and selling it at our local farmer’s market for 4 years. I feel pretty experienced, but days like today, I wonder if I know anything at all!! Any suggestions?

    1. Hi LuAnn!

      I think there is definitely some validity to the water amount being a factor, however, I have had glycerin rivers in soaps with 50% lye solutions – which is the biggest water discount you can apply safely. 😉

      The thing is, chemistry speaking, glycerin rivers are formed through uneven saponification. Higher water amounts can change how soap much soap heats up, cools down, and in general, how it moves through the chemical reaction of saponification. I was super thrilled to see Clara follow up her original post with a more detailed (and science filled!) post that gives a far better understanding of how water amounts are a factor in relation to what we already know about glycerin rivers being caused by uneven saponification: http://auntieclaras.com/2014/05/glycerine-rivers-trying-to-understand-them/

  3. Thanks for posting that link, I hadn’t read it yet. Very interesting, now I have some more experimenting to do!! My hubby is a Chemist, but has NO interest in soapmaking. I will have to get him to read those posts, since he is usually interested in the sciency stuff! 🙂

  4. One of the prettiest soaps I have ever made was full of glycerin rivers. They were so evenly dispersed it looked like I did it on purpose. I have tried for 2 years now to duplicate it but no luck. However, I am not giving up.

  5. Recently found your blog and so happy I did. I started soap making about a year ago and had pretty good luck so far……until recently. My last couple of soap logs seem to have shiny (not sure if its oils or EO’s) seeping through the parchment paper I use to line my wooden mold, and also rising to the top of soap log. Do you think that is a glycerin river? Or would that be something else? I would appreciate your comment on this.

    Note: I see that you also teach classes at the Nova Studio. Seriously thinking of taking some of your classes in June. So excited that I found you.

  6. I am with you, I think I know what I am doing after all these years , but then it happens. I do like the look though. I think it’s kind of cool.

  7. I’ve soaped using the heat transfer method. I used winter candy apple as my fragrance. During the heat transfer method my soap never got above around 100degrees while in the mold. Tons of gylcerin rivers. So my second try i soaped at around 115 instead of heat transfer, used a 10% water discount and put in my refrigerator to ensure it wasn’t over heating. No special additives. Distilled water and lye mix. My recipe is a combination of olive oil, coconut oil, Palm oil, Sweet Almond Oil and castor oil. I also used vanilla stabilizer . Any idea what I’m doing wrong. I’ve not seen any reviews that other people are having this problem with the scent. Any suggestions.?

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