Category Archives: Science!

Glycerin: The Good, The Bad, and The Ugly

Pretty much everyone knows handmade soaps all contain high levels of glycerin – some people even refer to certain categories of handmade soaps as “glycerin soap”. But why is that? And what does it really mean?

Well, the why is easy: Because chemistry. …what, you want more? OK, let’s trot out the saponification equation again (last seen in this post).

Image credit: V8rik at en.wikipedia.

Now, in this bunch of squiggles, the R represents a long “tail” of the fatty acid chain, of which the original triglyceride (in non-science talk, “fat” or “oil”) molecule has three. Lye comes in and smashes this three-tailed monster into four pieces, three of which are soap molecules (R plus some oxygen and sodium bits, which is to say, a long fatty tail on a water-soluble head, letting it glom up oily dirt particles and then wash away in rinse water).

But that’s not what I came to tell you about. I came to tell you about the glycerin.

The fourth piece, left over after the soap molecules are accounted for, is made of up what used to be the “head” of the triglyceride molecule, and is now known as glycerol. But because we all love to be confusing and can’t have just one name for anything, it is also referred to as glycerin and glycerine, and the term I prefer to use in this context is glycerin. With me so far? Awesome.

Glycerin is chemically a sugar alcohol, which really doesn’t mean much outside the chemistry lab, but people who know about such things will tell you it describes the carbon backbone represented by the framework in the above drawing and the OH groups tacked on to all the ends that used to have fatty acids on them. Those OH groups are HIGHLY water-loving (“hydrophilic”). They love water, and pretty much can’t get enough of it. It’s not enough for them to suck up water when they’re actually wet, they have to go around vacuuming it out of the air, too (which actually makes glycerin “hygroscopic”). Anything with a sufficiently high level of glycerin content (like soap) in a sufficiently humid environment (like a badly ventilated bathroom right after a shower) will shortly become all covered in little tiny beads of water (“sweating”) and eventually end up sitting in a puddle.

But it’s not all bad! Using soap with high levels of glycerin leaves trace amounts of glycerin on your skin, where it will indeed attract water from the air – but unless you’re in the rain forest (well, and probably not even then), it won’t attract enough water to make you actively damp, it’ll just help keep your skin from feeling itchily, ickily dry. This is one of the ways in which artisan soaps end up feeling so luscious and moisturizing on your skin long-term, and is definitely a solid positive on net, and the removal of glycerin from many commercial soaps (to make the soap harder, partially, but also because selling it to pharmaceutical and other industries is highly lucrative) results in the skin-tightening dry feeling that can result from using those soaps.

Still, as implied above, there are some down sides to using soap with high glycerin content. Glycerin is desperate for water, and showers are full of it. Since there’s so much glycerin in the soap, if it finds itself sitting in a puddle (whether one it coalesced out of oppressively humid air, or one it was left in due to a poorly-draining soap dish or a location next to a drippy shower head), it’ll soak that puddle into itself, and the water will permeate the entire part of the bar which is sitting in water, gradually dissolving it into a gooey, gucky, sticky, gelatinous blob of a mess.

Yuck, right? Yeah. The extent to which this will be a problem will vary significantly – some bathrooms only remain humid for a short time, and some soap dishes have good drainage or elevated bits to keep the soap from sitting in water, and in those cases a person might never notice a problem at all.

For those of you who aren’t so lucky, there are a few things you can do to minimize the problem. If you have a tub-style shower stall, store the soap at the far end, away from the shower head, and make sure there’s no water standing in its alcove when you leave the shower. If it’s just a stall, look for a place as drip-free as possible, or even look into adding a suction-cup soap dish above the level of the shower spray. If that doesn’t work, you might even consider removing the soap from the shower entirely and setting it in a different, less humid part of the bathroom. Soap dishes at sinks should have drain holes or ridges to keep the soap from sitting in water. At the very least, always store soap standing upright, not laying flat in the dish, to minimize the surface area which can possibly be in contact with any water which does appear.

Is this too much trouble to go to for care and feeding of one’s luxury handmade artisan soaps? Well, I find it well worth the effort, and I think you will, too. Your skin will thank you for giving it a try!


Why Use Silk in Soap?

Silk is far from a universal ingredient in artisan soaps, but it is increasingly common. And there are several reasons for that – but they all add up to it making the soap smoother, shinier, and, well, silkier – and but mostly stabilizing the lather, or foam. OK, how does it do that?

The answer? Protein. Proteins are the basic building blocks of all manner of things, and silk is almost entirely composed of protein and smaller amino acids. Dissolving silk into the lye solution at the beginning of the soapmaking process breaks the long proteins into smaller pieces which end up evenly distributed throughout the final soap. Even these smaller pieces, though, are still huge honkin’ molecules with lots of different parts, which is how they manage to do what they do.

And what is it they do? Well, anyone who has ever made a meringue has seen the efficacy of a protein-stabilized foam – and indeed pretty much all culinary foams benefit from the stabilizing effects of proteins in one way or another, from whipped cream to cappuccino to chocolate mousse. But before we can get into why this is the case, we should take a look at what a foam actually is.

In its simplest form, a foam is a whole bunch of little teeny bubbles separated by thin films of liquid. Seems pretty obvious, right? Sure. But liquid being what it is, and gravity being what it is, the liquid is going to want to run downward and eventually collect at the bottom of the pile, leaving nothing in between the bubbles but air. And since air was what was inside them in the first place, this pretty much means they aren’t bubbles anymore, they’re just – well, air. This will essentially always happen eventually, but there are some things we can do to make it happen more slowly.

What allows a foam to form in the first place is usually a surfactant, lowering the surface tension of water and creating conditions favorable to the formation of a film. But wait, I hear you say, isn’t soap itself a surfactant? Why do we need the protein? Well, if all we want to do is make the foam in the first place, we don’t. Soap will lather perfectly well on its own – just add water and suds up. But with the exception of some carefully-formulated shaving soaps and bubble baths, it doesn’t usually stick around very long, because soap is an insufficiently complicated molecule.

Proteins, however, as stated above, are huge honkin’ molecules, and have the potential to interact with themselves and each other in interesting and fairly complicated ways. Once a protein is denatured – for example, by dumping it into a crazy high pH lye solution – all of the parts of its structure that once held it together in the specific shape that let its do its job – the forces that make silk so incredibly strong, in this case – are flailing around without anything to do, like the hook half of a Velcro strip bereft of loops. But wait! That piece over there has loops! It’s not a perfect fit, maybe it only fills 5% of the hooks, but hey, it’s better than nothing. So they end up very weakly bonded, one to another, all through the solution. This trait of proteins is what gives soup stock its “body” and “mouthfeel”, and it’s what helps these bubbles stay put longer.

So that’s why I put silk in my soap. Is that the only source out there for soapy proteins? Absolutely not! Other common protein sources in soap include milk (often goats’ milk) and oatmeal, and I also get a protein boost from the beer I add to my Hops in the Shower line. Some people use other fibers, such as angora wool. Now, not all proteins are created equal, so each of these protein sources will have a subtly different set of effects on the soap. But in nearly all cases, the foam stabilization effects will be in play in the lather they generate.