The other day I fried up some potatos and cheese flautas in canola oil. I later noted that the atlas mason jar I was storing used cooking grease in was full. I’m not much for bacon, and tend to fry only meats lean enough that there’s no point in collecting the oil, so the contents of the jar is exclusively vegetable oil used for deep frying, along with various food residues of whatever I’d been frying. It has a sort of fur of such carbonized relics that have settled to the bottom of the jar. I decided it was time to make soap.
I’ve never made soap before, which is why I’m calling this a “science experiment” rather than, say, a “how to.” It’s just as likely to be a “how not to.” As of this writing (that is as I am writing this particular paragraph) I have still never made soap. This is a speculative introduction based on an intention. It is entirely possible that instead of soap I will make something that could scientifically be described as a “gloppy mess.” But I am going to leave this record as it is written, which method suits the scientist in me. You dear reader get to ride the text time machine, compressing the coming days of experimentation into mere minutes’ worth of droll and erudite text.
There’s another reason this is not a how-to, namely safety. Soap is made with lye, and lye is the very definition of caustic and quite literally dangerous. I’ve got some experience in dealing with nasty chemicals from way back when I was studying chemistry, but God forbid anyone go try to make soap on their own on the basis of this little report. If you get the yen to try it yourself, buy a decent book on the subject, acquire the appropriate safety equipment, and follow the directions precisely.
So yes, I’ve never made soap before but I’m aiming to make me some soap. I’m not banking much (like, say, staying clean in the immediate future) on the outcome because as little as I know about making soap, I’m guessing that the better recipes don’t start with “beginning with a mason jar full of nasty old cooking oil...”
But I’m know I’ve got a book on the subject floating around somewhere, and ye olde internette can always make up the gaps these days. It’s the experimental nature of these things that make them fun.
The chemistry and function of soap
A water molecule has no net electrical charge, but the nature of its composition make it something like a magnet - one side has a positive electrical character and the other negative. This is called polarity. This is one of the reasons water is such a good solvent, particularly of other polar things - it can attract and hold positive or negatively charged molecules in solution. Oil and water don’t mix because oil is apolar: there is no charged area of the oil molecule for water to attract. And therein lie the two problems of cleaning with water. First, it won’t dissolve oils and greases well. Second, water’s polarity limits its ability to clean because it sticks so well to itself (positive side attracting negative side) that it may tend to “clump” together rather than insinuating and dissolving a particular soil.
Enter soap. Soap has a unique electrical character - one component is polar, the other is apolar. The apolar component is like an oil - a long chain of carbon molecules with no charge, and thus repellant to water. The polar component has an electric charge (chemically soap is actually a salt) and thus is attracted to water.
This composition has two effects. The first is that the apolar component of soap can attract and thus dissolve oils. The second is that the polar component of soap is attracted to water molecules and so soap can break up water’s attraction to itself, making it more able to insinuate itself into all the nooks and crannies of whatever needs to be cleaned. The old kid’s science experiment, where you suspend a layer of pepper on the surface of a glass of water, then dip a bit of soap into the glass, making the layer of pepper all rush to the sides of the glass, is based on this property - the surface tension of water is created by water molecules’ attraction to one another. Soap breaks up that attraction.
So how is this unique compound that makes up soap created? Soapmaking takes advantage of the chemical nature of oils. An oil, like a vegetable oil, is largely composed of molecules called triglycerides (a term you’ve no doubt heard with relation to nutrition and health). A triglyceride is composed of three (that’s the tri- part) fatty acids - long, apolar chains of carbon molecules with an acidic component on one end. The three fatty acids are attached to a backbone formed by a glycerol (that’s the -glycerided part) molecule. Glycerol is an alcohol - meaning it’s chemically active component is formed from oxygen bonded to a hydrogen molecule. The alcohols we are most familiar with, like drinking alcohol or rubbing alcohol, have only one O-H group. Glycerol has three of these groups. Each of the three oxygen atoms in these groups are bonded to the polar, acidic component of one fatty acid chain.
Being chemically bonded to the glycerol molecule keeps the polar, potentially water-attraction component of the fatty acids all locked up, and thus the triglycerides in oil are insoluble in water. So making soap is a process of chemically detaching the fatty acids from their glycerol backbone and replacing it with something that will create a free polar terminus on the fatty acid chain, allowing it to be attracted to water molecules and so dissolve in water.
Since the chemically active component of a fatty acid is, well, an acid, it will react with the chemical opposite of an acid, a base. Like all alcohols, Glycerol is a base - but a much stronger base can break the bond between the fatty acid and the glycerol. Common household lye is sodium hydroxide (NaOH), one of the strongest bases (and certainly the strongest that cheap and readily available). It’s chemically similar to what was probably the first base used to make soap - wood-ash derived lye, which is primarily potassium hydroxide. At the consumer level pure sodium hydroxide is still sold as a drain clog remover (and is a major component of many other commercial drain clearing compounds).
And really, that’s all there is to the basic manufacture of soap: lye in solution with water is mixed with oils, rips the fatty acids free of their glycerol backbone, and reacts with them to form the salt called soap.
In theory. In practice, of course, the world of physical matter tends to be a bit more complicated than that, as we will see.
Making the Soap
Step one for me was to clean up the cooking oil. Frankly, I’d be better off not using this oil at all for a variety of reasons (thought the one most will probably relate to is, as my wife said, “that’s gross”) - but recycling it is part of my plan for the whole experiment so I need to clean it up. This is accomplished pretty simply, by boiling the oil in twice as much water with a bit of vinegar and lemon juice added to promote the removal of impurities and eliminate odor. After cooling most of the clean oil separates from the water; a certain amount is left in a semi-mixed in-between layer called an emulsion. There are all sorts of tricky techniques for separating an emulsion, but I take the shortcut of simply ladling the clean oil off the top and leaving the emulsion behind. I lose about a quarter of my volume of oil.
Canola alone isn’t an ideal oil for soap, and anyway what I’ve collected would not be enough to make a decent sized batch. Luckily I have a couple other components that are well-suited to the experiment. The first is coconut oil - an oil prized for soap-making because it delivers a rich lather. I don’t know why I have a jar of coconut oil. I bought it for some reason, but I don’t appear to have used hardly any, and it’s been sitting in the cupboard for years. I also have the better part of a bottle of extra virgin olive oil that has been ruined by getting too cold (apparently the back of the kitchen cupboard that is against an exterior wall gets pretty darn chilly in the winter): fatty solids have separated out of the oil and are sort of clumping around the bottom. Culinary disaster! The oily ratios will be all out of whack. Some heat will redissolve the fats, but heating extra virgin olive oil prior to further storage sort of defeats the purpose of buying it in the first place: time for a new bottle for cooking, and I’ve got a use for the old one.
So, I heat the two additional oils to dissolve all the fatty solids, weigh them, and mix them all together. The internet provides an automated calculator to determine how much lye is required to react with the volumes of oils I’m using. Now it’s time to start working with lye, the dangerous part of the process.
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There it is, all measured out and ready to be added to the (also measured) water in the glass flask. I’m creating a very strong, caustic solution, so I use heavy rubber gauntlets, and go about my business at a slow, cautious pace.
The chemical reaction of the lye dissolving in water is so active that it actually heats the water to around 200 degrees F. It has to cool a considerable amount before it gets added to the oil.
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There’s everything all set to go, my bowl of oil and flask of lye solution. All that’s needed to get the party started is to slowly mix the two together and stir.
And stir. And stir. And stir.
And stir.
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Time passes, and more time passes, and I begin to become concerned because my soap solution is not getting thick enough to “trace” - the point where, when you drizzle a little of the mixture over the surface, it forms a visible trace for a few moments before it sinking back in. I’m getting bad flashbacks to organic chemistry labs in college, the final synthesis project, I’m right back there in the old O-chem lab, holding a bubbling flask of what is supposed to be turning into a nice, simple colorless liquid, but has instead turned a vivid green and is emitting a noxious brown smoke that has sent my fellow students fleeing to the far side of the room (yeah, it all actually happened). I got a C in lab that quarter. This “soap” is nothing less than a pathetically obvious symbol of all the times in my life that I played it fast and loose and invited failure as a result.
I decide I better get a grip. What’s gone wrong? Unfortunately, there is no shortage of culprits (and no reason to believe that there couldn’t be multiple problems in the works). Real soapmakers use time-tested (or carefully and experimentally concocted) combinations of oils to create soap with desirable characteristics: I used whatever was at hand, in whatever amounts there were. Measurement error seems a likely problem: I used the only scale I own, a spring-type postal scale. I knew from the outset that this was a problem, but I wasn’t about to go spend money on a good scale for one experiment. Given that the soap reaction seems to have stalled, insufficient lye seems like a probable, fundamental cause. The small size of the batch would compound these measurement errors, as any erring measurement represents a larger percentage of the whole. I also suspect an issue with temperature control (the same issue that fouled that misbegotten long-ago chemistry experiment). I’m doing what’s called a cold-process method, where no external heat is added after the components are mixed: but certainly both the oil and lye should be within certain starting parameters and I just guessed.
That things don’t seem to be going so well, then, is disappointing but not exactly surprising. Nevertheless, now I’ve got this bowl of slightly gloppy mess and I have a decision to make. Either I send the whole thing down the drain with copious amounts of hot water, or I abandon the plan, such as it is, and start messing around.
I chew my lower lip, giving the mess a moody and desultory stir. What the hell. Of all the possible errors the only one I can possibly effect now is the possibility of insufficient lye. So I mix up some more lye solution (eyeballing it this time; there seems little point in maintaining the illusion of “measurement” at this point) and start slowly drizzling it into the glop. Drizzle, stir, drizzle, stir, drizzle stir. Whatever happens at this point the resultant mixture is going to be suspect because of the imprecision of the technique. Not enough lye and it will never set and cure, too much and the soap itself may be caustic enough to, well, cause a chemical burn. Maybe I can sell it on eBay. “Weird, messed-up soap, may be unsafe.” There must be some freak out there with a yen to wash up on the edge.
It starts to trace. Well, it’s pretty much out of my hands now: I pour the mix into a glass dish, cover it and wrap the whole thing in a towel. It needs to set for 24 hours now.
Results: Soap?
Moment of truth. I unwrap the towel, take off the cover, and have a look at what I hath wrought.
Well, immediately I know that the experiment cannot be called an unqualified success. Can you spot what’s wrong with this picture?
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That’s right, that big dark depression in the middle of the batch. That ain’t right. But I intend to carry this thing right through to its appropriate conclusion, so I cut up the mass, discard the most egregiously flawed chunks from the middle, and set the rest out on slabs of cardboard to cure. I can note at least that the chunks and leavings of the cutting had some distinctly soaplike properties, and that the residue sudsed up very soapily when I cleaned up the pan.
But here’s the punch line - the soap has to cure 6-8 weeks before its done. So there will be some kind of soap epilogue (a soapilogue, if you will) some time in early May, when I will take my fate into my own hands and actually wash with the soap, and make my report on the outcome.
I still think there’s something to be said for the diving in approach. I may well acquire the appropriate equipment and do this thing properly at some point in the future, but it is instructive to head into something not knowing too much, using what’s available, and finding out firsthand what can go right, and wrong. Bear these subtleties in mind, the relative complexity that can lurk beneath the surface of the simplest necessities we take for granted, next time you lather up.
this is what is up with this.
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