A month ago I posted about my brine design experiment. I put soap made with brine (saline solution) next to the same soap made with plain water and found that the brine turned the soap more opaque and much lighter in colour. For my experimental soap I used a balanced formula with about 20% coconut oil.
Making snowy white soap without the addition of synthetic pigments like titanium dioxide and zinc oxide is something of a holy grail among soapmakers; almost as much of a holy grail as achieving true red in soap. Hence my brine design experiment with brine soap and plain-water soap next to each other caused some discussion in the soapmaking community.
What About Coconut?
Shortly after my post somebody asked if you really needed the brine; couldn’t you just make a plain-water soap with 100% coconut oil instead? As we know coconut oil makes very white soap; possibly whiter soap than any other common soapmaking oil.
100% coconut soap is an effective de-greaser well-suited for laundry and stain-removal use but harsh on skin. To make pure coconut soap more skin-friendly and better suited as bath soap soapmakers typically make it with a high superfat, i.e. with lots of extra oil as a kind of built-in conditioner. Coconut soap with a high superfat tends to divide users into those who really like it and those who prefer milder and more balanced formulations.
In any case I thought it was a fair question that deserved a bit of investigation. In my previous experiment I had used a blend of oils. None of them were dark in colour but they would still make soap with a more yellow tone than refined coconut oil. So why not try the same experiment with 100% coconut oil to see if coconut soap made with plain water would hold its own against coconut soap made with brine?
White On White
I made the previous brine design soap with water at 20% of oil weight. But, in my experience pure coconut soap is better made with more water. Coconut soap gets very hard very quickly – even with plenty of water content. It’s an old soap hustler trick to sell uncured coconut soap: water is cheaper than oil and because the bar is very hard anyway it’s hard to tell that a substantial part of both weight and volume is water rather than cured soap.
In this case though, beefing up weight and volume was not an objective. Rather, I wanted to be able to make decent cuts into a loaf of soap without breaking my cutter or making the edges of the bars crumble. Instead of water at 20% of oil weight I now did water at 29% of oil weight.
With this difference in water content I now realise that it makes more sense to think of salt content in relation to oil rather than in relation to water (as in strength of saline solution). Water is volatile and will evaporate whereas oil and salt don’t. In the brine portion of the pure coconut soap I kept the salt:oil ratio at about 4.5% as I did in the previous soap, but since I used more water the saline solution was now quite a bit weaker.
To make the soap suitable as bath soap I decided on a 25% superfat.
Invisible Brine Design Swirls
Just like before I made three equal lye solutions; one with brine and two with plain water. I blended light, non-discolouring essential oils into the oil before dividing it into three equal parts. Once all three batters had been blended to very light trace I poured each batter in its own compartment using two lengthwise dividers. Brine soap in the middle and plain-water soap along the sides.
Swirling brine design soap is a bit of a leap of faith. Unlike the Ghost Swirl where the low and high-water soap batters have distinct shades there is no difference in shade or colour between brine soap batter and plain-water soap batter so you can’t really see much. You just swirl and hope it turns out.
The higher water content caused the coconut soap to go through full gel phase..
As I unmoulded the log about four hours after pouring it looked quite spectacular against the afternoon sun.
Next to the opaque brine portions the plain-water portions really look remarkably translucent.
The Brine Design Cut
The horizontal cut of the swirled soap was very pretty. Something quite retro about this design.
So, this is freshly cut 100% coconut soap made with plain water and with brine side by side. As water evaporates the plain-water soap will lighten up to some extent, but because it will continue to be translucent it will never look nearly as white as the opaque brine soap.
Now, a week later, the surface of the coconut soap has dried quite a bit, but the contrast between plain-water and brine soap is still clear. Compared to the soap made of blended oils the 100% coconut soap has slightly less of a yellow tone, but the blended soap made with brine still looks whiter than the 100% coconut soap made with plain water. And the 100% coconut soap made with brine is much whiter than the plain-water coconut soap.
But what if you prevent your 100% coconut soap from gelling? Non-gelled soap is less translucent and because of that it appears lighter. I’d say that’s a good idea in theory, but hard to achieve successfully in practice – unless you are using small individual moulds.
Saponification generates heat and heat pushes the soap into gel phase. The more water in the soap the lower the temperature needed for the soap to enter full gel phase. In order to successfully prevent a relatively large body of soap from gelling from heat generated inside the soap you need to keep water content low. You can refrigerate the saponifying soap if you like but unless your mould is small a full-water coconut soap is likely to ‘lapse’ into gel phase in the centre anyway.
You can do a steep water discount, but as mentioned earlier that will make 100% coconut soap so hard so quickly that cutting a log can become tricky. The best is to cut it while it’s still hot but that means that you have to watch it carefully; you might damage the soap, and you might burn your fingers. It’s doable, but it seems easier to just add a bit of salt to a gentle and balanced recipe for a natural white appearance.
As an update on the first brine design soap I can say that it feels lovely in use. The small amount of salt doesn’t reduce lather noticeably but it somehow makes the lather finer and more cushioned. Lotion-like, as they say. The essential oil blend of peppermint, rosemary and eucalyptus is like a cool breeze – it’s a really nice soap.
This blended formula isn’t extra high on oleic acid but in a comment to my previous column somebody mentioned that they make olive oil soap with seawater (a form of saline solution) to reduce the mucilaginous feel typical of oleic acid soap. I think I might try making a 100% olive oil soap with brine next. In the meantime: happy holidays everybody!