January 8, 2001
As some of you may or may not know, Keith and I occasionally engage in soapmaking endeavors. It's something Keith has been doing since before we moved in together, and lately I've taken an interest in the workings and have even done a batch or two of my own.
Before I tell you about the debacle that just happened, I should give you some basic facts about soapmaking. I promise not to get too technical.
Soap is made by mixing lye and fats together. The lye and the fats combine to form soap and glycerine. The art in soapmaking arises from the fact that you can choose 1) which types of fats to use in the soap, 2) what sort of scent to add to the soap, 3) what additives to put into the soap, and 4) how much extra fat to put into the soap. By "extra fat", I mean fat that does not saponify. "Saponification" is the process whereby fats and lye react to form soap; the home soapmaker does math to figure out exactly how much lye is required to saponify a certain amount of fat. You then decide how much extra fat to add in. The extra fats and oils will not saponify; they will remain in the soap, more or less in their original state. This contributes to a milder and gentler soap, and can be really good for the skin. We tend to add in 10% more fats and oils than are necessary for total saponification. We usually also add in glycerine, aloe vera oil, or other additives at trace. ("Trace" means the point when the stirred soap solution becomes so thick that a trail of soap drizzled across its top will leave a raised trace before sinking back in.)
So now you know (basically) how soap is made. Right now we have a ginger soap and an almond-vanilla soap drying on the racks. The ginger soap came out fairly well; it is cleansing and mild, but doesn't have much lather to speak of. The almond-vanilla soap is fantastic. It lathers beautifully, leaves my skin soft, and has tiny particles of oatmeal in it to assist with exfoliation.
So this brings us to tonight. Or, more accurately, last night. I was reading in one of our soapmaking books about this stuff called "kukui nut oil", which is an oil produced from the Hawaiian kukui nut. The book said that it made a superior soap with a good texture, so I wanted to try it out. We went to the supply store, and sure enough they had it, but by God was it ever expensive. They wanted $25 for 8 ounces. That's a lot. So Keith and I debated, and we decided that for the first time ever, we would do a control batch and an experimental batch. One would have the kukui nut oil and one would not.
So we bought a small amount of kukui nut oil and went home. I volunteered to do the math, and Keith graciously allowed me, even though he was the math major and I was the pie-in-the-sky liberal arts major. I think he trusted me because the almond-vanilla soap was entirely my own creation, so obviously I had been able to do the math on at least one previous occasion. I did my figures, multiplied in the 10% lye discount, and presented them to Keith, who began measuring lye while I opened doors and windows in preparation. (You really don't want to breathe lye fumes; trust me on this one.)
Soapmaking went, as soapmaking does, and at the end of the evening we had a batch of spearmint-scented soap, complete with kukui nut oil, poured into its mold.
Tonight Keith is away at his gaming club, so I volunteered to do the control batch by myself. The idea was to exactly recreate the recipe from the night before, except to adjust the other ingredients proportionately to make up for the lack of kukui nut oil.
The first thing I did was to prop our gallon plastic jugs of coconut oil and palm oil against the gas stove. We tried this last night with good results. Coconut oil and palm oil are both solid at room temperature -- very solid. So solid, in fact, that it can take up to 45 minutes to chip out 40 ounces of the stuff. It is hard labor, and not very pleasant. So I came up with the bright idea of propping the jars against the stove, so that the heat would soften them.
And so, with the plastic jugs propped against the stove (perhaps you see where I am going with this), I sat down to do the math. It should have been mostly the same as the math from the night before, with a few slight differences.
After a few minutes, I noticed an odd burning scent. I looked over at the stove to make sure nothing was catching on fire, and something was catching on fire. For once, my paranoia was completely justified. I leapt out of the papasan chair, knocking the bowl part completely off the stand part, and yanked the two plastic jugs away from the heat of the stove.
Nothing actually caught on fire, but there was a gigantic hole burned through the side of the palm oil. Luckily, the hole was above the level of the now-liquefied palm oil. I set the jugs down on the kitchen floor and spent the next fifteen minutes scraping melted plastic off the glass front of the stove with a butter knife.
God, my life is glamorous.
After that somewhat unsettling experience, I sat back down to finish the math. Very soon I noticed something amiss. The lye value I'd come up with was different from the lye value we'd used last night. It should have been nearly identical. I went back to yesterday's figures to check the math...and noticed a calculation error. It happened when I multiplied the amount of KOH necessary by the conversion value, to get the amount of NaOH necessary. (For some reason, saponification values in soapmaking charts are given using KOH instead of NaOH, so you have to convert.)
I rechecked the math at least twenty times. I sat there punching numbers into the calculator for at least half an hour. Once it become obvious that yes, I had in fact made a math error, I tried for a very long time to reproduce the error, so that I would at least know how it happened. No dice. I didn't divide instead of multiply, I didn't transpose digits, I didn't hit "3" instead of "4", I didn't leave out a digit at the end.
In short, I have no idea how it happened, but we used exactly 5 grams more lye in the soap than was necessary to saponify 100% of the oils. My figures were off by 30 grams; 25 of those grams were accounted for by the fact that I'd used a 10% discount. But 5 grams were left over, even after the discount. 5 grams of unsaponified lye.
This is what we in the soapmaking biz like to call a Bad Thing.
It's possible that we had enough wiggle room in the measurements that the soap will be okay to use. We won't know until it hardens and cures and we can test a bar in the shower. Don't worry; the lye in it won't burn straight through our skin, the way undiluted powdered lye would. It will just be harsh and drying. And even if all of the lye was saponified, the soap will still not be as mild as we'd planned it to be. Those extra fats and oils really make a difference in the final soap, and all of ours were used up by the excess lye.
ME
Hi, is Keith there?
GUY AT CLUB
Hang on a sec. (shouts) Yo, Keith!
KEITH
Hi, this is Keith!
ME
It's me. I did two bad things.
KEITH
Um, okay.
ME
Remember how you warned me about putting the plastic tubs right next to the stove?
KEITH
Oh, hon.
ME
Yeah. I burned a hole right through the side of the palm oil.
KEITH
Wow. Was it above or below--
ME
--below. Also, I screwed up the math yesterday and we used 5 grams more lye than necessary to saponify 100% of the fats.
KEITH
Aw, hon.
A ten-minute conversation followed, during which there was much self-recrimination on my part, and admonitions "not to beat yourself up" by Keith. We discussed our options and decided to go ahead and try the soap once it cures, just in case it comes out okay, and also decided that we would try the experiment again...just not tonight.
And that is the story of my soapmaking debacle.