Coffee River Soap and How To Make Glycerine Rivers

A while ago fellow soapmaker Karol Dulmanis posted a picture of a coffee soap in one of the Facebook groups I belong to. The beautiful soap had an interesting dappled look with light translucent soap contrasting with areas of dark coffee grounds. The effect looked just like tortoise-shell and Karol wondered how one would go about creating this kind of glycerine rivers in coffee soap.

“Use full water and keep it in gel phase for as long as you can,” I replied and scrolled on.

It’s been quite a while since I wrote my first articles on glycerine rivers (you can read those articles from 2014 here and here), but I still find the rivers fascinating. Because I can and because it suits the particular style of soap I normally try to make I’ve eliminated ’glivers’ in my own soapmaking despite ovenprocessing almost all soaps and working extensively with pigments including titanium dioxide. But I’ve seen countless pictures of stunning glycerine rivers and they all still make my heart beat a little faster.

The tortoise-shell effect in Karol’s soap was striking and the picture of it had etched itself onto my mind – thank you Karol for the permission to post the picture here! I kept thinking about it and it occurred to me that maybe I shouldn’t just shoot advice from the hip. Maybe I should actually put my money where my mouth is and try creating something like that myself: check if all that glycerine river advice I keep dishing out to other soapers is actually worth something.

Also, I could smell an experiment in the air and that’s always a treat. So, for the first time in a very long while I set out to make glycerine rivers again.

What are glycerine rivers?

Now, let’s recap: what are glycerine rivers?

’Glycerine rivers’ is a term commonly used to describe a veined, mottled, crackled appearance in coldprocess soap. The cut soap looks curdled with ’rivers’ of unpigmented, translucent soap running between ’islands’ of pigmented, opaque soap. Glycerine rivers are generally poorly understood and they tend to pop up in soaps and designs where they’re unexpected and undesired.

But what are they actually? There are some imaginative myths surrounding glycerine rivers so lets first bust some of those.

First of all glycerine rivers are NOT glycerine (or glycerin if that’s your spelling of choice). They are not “solidified glycerine” or “glycerine that develops in soap that goes through gel phase”. Glycerine – or glycerol – is an end product of the saponification reaction whether or not the soap goes through gel phase. Coldprocess soap with visible glycerine rivers is no richer in glycerine than a soap without rivers.

What the precise etymology of the term glycerine rivers is I don’t know, but the typical unpigmented river veins do look transparent like transparent ’glycerine soap’ – so maybe that’s how the term got coined. Today it’s an established and widely used term despite being a bit of a misnomer.

In this article DeAnna Weed explains what glycerine rivers actually are. They are the first fatty acid soap(s) to solidify when soap in gel phase gradually cools down over an extended period of time. Pigments and fine particles will migrate away from the solidifying soap and will congregate in the soap that’s still gelling. What we see as pigmented areas in a cut bar with glycerine rivers is the last soap to solidify in that bar. In practice those first soaps to solidify tend to be soap of stearic acid and soap of palmitic acid while soap of e.g. oleic acid tends to stay in gel phase longer. It’s a separation of soaps of different fatty acid content.

And that’s how glycerine rivers come into being.

How can we make glycerine rivers?

So now that we have an idea of what glycerine rivers are and how they happen, what can we do to make them happen at will?

A diehard myth is that glycerine rivers are caused by titanium dioxide. They’re not. Titanium dioxide is a pigment with fine particle size and excellent opacity. It will congregate in gelling soap, move away from solidifying soap and make the crackled or veined appearance of the soap extra visible, but it doesn’t cause that structure.

The first prerequisite for making rivers happen is that the soap goes through full gel phase. In full gel phase soap molecules and pigments are mobile and can migrate to make the river patterns visible.

The second prerequisite is that the soap stays in gel phase for an extended period of time. In this article Kevin Dunn found that glycerine rivers become more pronounced the longer the soap stays in gel phase. In her article DeAnna Weed maintains that slow cooling, i.e. slow, gradual transition from gel to solid is crucial for crackling to occur.

So we need to get the soap to gel and we need to get it to stay in gel phase for an extended period of time and to cool down slowly.

This is where water comes in handy. A high water content does not cause glycerine rivers directly, but as Kevin Dunn clearly shows in Scientific Soapmaking a high water content causes the soap to enter gel phase at a lower temp than a low water soap. Further more saponification is slower in a high water soap than in a low water soap, a high water soap stays in gel phase longer, and it moves out of gel phase more slowly than a low water soap.

Those are exactly the conditions we want for our river-making: extended gel phase and slow cooling. We can arrange those conditions in a low-water soap too by clever heat management first of mixing temps and then of ambient heat – or by harnessing internal heat generation in a large enough body of saponifying soap. But if we use high water and insulate the mould carefully, we’re likely to have close to perfect conditions even in small batches without having to add any ambient heat.

Coffee rivers

Karol’s soap was a coffee soap and I quite liked the idea of making coffee soap. I drink lots of coffee here at home, always black, never with sugar, but I hadn’t made a coffee soap in many years. Coffee grounds are an effective way of removing kitchen odours from your hands so scrubby coffee soap makes nice hand soap for kitchen use.

In addition I liked the idea of making a glycerine river soap without conventional colour pigment. As I said soapmakers often blame the rivers on titanium dioxide, but the truth is that all you need to make rivers visible is a sufficient concentration of opaque particles that disperse rather than dissolve in the soap batter.

To make things simple I decided to use plain water for my lye solution and then add finely ground coffee beans to the oils before adding the lye. I added dry coffee grounds; moist grounds often get a round halo around them and that wasn’t the effect I was after here. I gave my beans a very thorough grinding and turned them into a fine powder. I was making scrubby kitchen soap, and scrubby is good but nobody wants to wash their hands with something that feels like barbed wire.

I made the soap with a 2.5:1 water:lye solution. I normally soap with much less water than that, partly because I try to avoid glycerine rivers, partly because I don’t want to risk the soap overheating when I ovenprocess it (you can check out how water content is related to overheating in this article), and partly because I see little point in unnecessarily extending evaporation time.

Now I felt a bit reckless watering down my batter like that. But after I added some coffee fragrance it went into the mould and then into a 60C (130F) oven which is my standard ovenprocessing temp. There it stayed for a couple of hours after which I turned off the oven and left the soap inside to cool down slowly.

The outside of an experimental soap log is always something of an enigma; you never know exactly what you’ll find inside. Cutting this log I got a stunning, even web of fine rivers running throughout the soap. Pretty much a textbook example of glycerine rivers – without any conventional colour pigments.

It wasn’t the beautiful, large tortoise-shell pattern of Karol’s coffee soap, but the rustic weathered ’leather’ look is perfect for a scrubby kitchen soap. As expected from a high water soap this one also developed a handsome dusting of soda ash on top:

I can’t tell exactly why the river pattern on my soap is finer than the pattern on Karol’s soap. We didn’t exchange recipes so the oil formula, precise liquid content and amount of coffee grounds used may well be part of the explanation. But given Kevin Dunn’s observation that heat and extended gel phase accentuate rivers I’m guessing that slightly higher oven temperature, perhaps for slightly longer would have given wider rivers.

Red rivers

Encouraged by my high-water success I decide to try my fast-moving Kir Royal fragrance oil with high water. I made some more 2.5:1 lye solution, but then I got distracted and didn’t get to make the soap until a couple of days later. In the meantime the design for the planned high-water soap changed in my mind a few times over and in the end I scrapped my plan for a layered look and instead I did a beautiful solid colour design with deep red iron oxide and a gold-painted top. When the soap was in the mould I casually popped it the oven on 60C like I always do. Only an hour into the ovenprocessing did it occur to me that this soap had lots more water than I usually use – in combination with the red iron oxide pigment. I now realized that I was in the somewhat involuntary process of ’baking’ rivers there in my oven. But since I figured the harm had already been done I decided to keep the soap in the oven for an extra hour, just to see what that would do for the rivers.

It was worth the wait because those rivers turned out spectacular. Who needs swirling tools and several colours when a single-colour soap can do this all by itself – with a little help from water and heat?

Of course the same concerns apply to this soap as to the coffee soap: how can we manipulate the rivers to have the kind of look we want? An even web of ultra fine crackles or bold streaks like the Amazon river cutting through the soapscape? Once again I guess that the relation between water content, temperature, and time is crucial. By tweaking those, everything else equal, you can probably create exactly the kind of river structure you like.

The red soap had a highly accelerating fragrance oil added at emulsion and that may have increased the rate of saponification and heat generation resulting in wider rivers. Or maybe it was the finer particle size in the pigment, or maybe I just kept it in the oven for longer. Or maybe all those conditions contributed..

Glycerine river dents

One of the glycerine river mysteries that I haven’t seen explained anywhere is the ’riverbed dent’: the indentation of the glycerine river that occurs immediately as the fresh soap is cut. This indentation may get more pronounced as the soap cures and warps, but since it’s there from the very beginning it’s not caused by uneven evaporation but by something else.

This is my theory: Soap in gel phase expands with raised temperature. As the temperature decreases the soap contracts and solidifies. We know that the unpigmented rivers are soap that solidifies at relatively high temp. Meanwhile the surrounding soap is still gelling and expanded. As the temperature drops further the surrounding soap also starts contracting pulling away from the previously solidified soap creating negative pressure in the solidified soap. As you cut through a river the pressure is released and the fresh soap pulls back on itself. Hence the indentation.

I stand to be corrected on this, but until I see a better explanation I’m sticking to this one.

How to avoid rivers

Well, now that we’ve been through how to successfully make glycerine rivers let’s recap how to avoid them if that is what we want to do:

No gel – no rivers, so avoid gel phase. This is best done by using water sparingly AND keeping mixing temps low. By using little water we keep the soap from slipping into gel phase at relatively low temp. If the soap does enter gel phase frugal use of water will ensure that saponification is quick and we get quick, short heat peaks rather than slow, extended gel phase.

This really works. Under normal circumstances I soap with water below 25% of oil weight and mix at room temp. Then I ovenprocess at 50-60C and I never have rivers in my pigmented soaps – even if I leave the soap to cool down slowly in the oven with the light on. This soap has plenty of titanium dioxide, iron oxide and ultramarine. It was made with the same oil formula and ovenprocessed the same way as the red soap above, but it was made with a 1.5:1 water:lye ratio and shows no signs of glycerine rivers:

Rivers or no rivers is a matter of choice and process management rather than a matter of chance. If we choose rivers I’m fairly convinced that we can learn to control and manipulate the appearance of those rivers. Until I figure out how to do it Karol’s tortoise shell soap will be the ‘gliver-goal’ soap for me.