The Fugue

If my last post made your head spin, you’re not alone. It made mine spin too when I was conceiving and writing it.

For your sanity and mine, I have put together a soap calculator spreadsheet. You tell it the precision of your scale, how much of each fat you want (sorry, you have to specify the saponification value too, but there’s a reference chart included), and your target lye discount. It tells you how much lye and water or milk to use. It also tells you how the measurement error effects your expected lye discount, and warns you if your soap might turn out lye-heavy. You can easily scale the recipe arbitrarily.

Download the calculator and my recipes at http://hans.fugal.net/soap.

Have you ever wondered what significance the measurement error of your scale has in making soap? What, you didn’t realize your digital scale has measurement error?

If your scale has 1-gram precision (the norm these days), then if it says 42 grams it actually means that it most probably is between 41.5 grams and 42.5 grams. The possible measurement error is ±0.5g.

What does this mean in measuring ingredients for soap? Well, there are two extremes: lye surplus and lye deficit (or inversely, fat deficit and fat surplus).

On the one extreme, you may have 0.5g more lye than the scale says, and 0.5g less fat than the scale says. In that case, the extra 0.5g lye is actually close to 4 grams worth of fat. The exact value depends on the saponification value of the fat in question. For example, olive oil has a saponification value of 0.134, so 0.5g/0.134 = 3.7g worth of oil. That means that if you do indeed have an extra half gram of lye, you need 3.7g more oil than the recipe called for (for simplicity, assume the recipe has no lye discount/superfatting). Now factor in the possibility that you have half a gram less oil than the scale says, and you need 4.2g more oil to be 100% sure you are not lye-heavy. Of course your scale only does 1g increments, so you have to bump it up to 5g. So, regardless of the recipe size, if you add 5g oil to the recipe, you’re sure to have at least the nominal superfatting, but perhaps more. Actually, probably more.

What about the other extreme—a lye deficit? If you have 0.5g less lye than the scale says, and 0.5g more olive oil than the scale says, then you have 0.5g/0.134 + 0.5g = 4.2g extra oil. Add that to your 5g that you added to be sure you’re not lye-heavy, and now you’ve got about 9–10g more oil than the recipe calls for in the most lye deficit case.

Now, we want to add the first 5g to a non-superfatted recipe, for sure, so we know we’re not lye-heavy. Then, the scale threatens to add another 5g, so it’s entirely possible we get more fat than we are willing to tolerate.

What kind of impact do those 10 grams actually have? Well that depends on the size of the recipe. For most recipes you’ll find on the internet, that 5 grams will be less than 1% of the total weight. No big deal. But if you, like me, are experimenting and making quite small batches it becomes significant. I like to aim for 1–5% superfat, but I’d be ok with 0–8%. So if I want no more than 8% superfat, and I add 5 grams of oil to be absolutely sure I don’t go below 0% superfat, and the scale adds another 4.2 in the worst case, then I want a minimum batch size of 9.2g/8% = 115g (before water). That’s a nice one-bar batch size.

Well and good, as long as you’re not trying to observe the effects of superfatting, since you have such a wide range of possible actual superfat. For that you’d have to break down and make larger batches.

But what is the expected value of your superfatting? The extremes are actually less likely to occur than something much closer to the actual reading. As a simplification, just take the actual reading to be your expected value. So if you add 5g oil to a 120g batch, then you probably have about 4% superfat. 4±4% superfatted soap. It’s alright by me.

So, a pure castile soap one-bar ingredient list:

102 g olive oil
13 g lye
25–30 ml water or milk (preferably goat's milk)

So in summary, if you have a 1g scale and you make small batches, the above is important to understand and take into account. If you have a 1g scale and make medium to large batches, then you are going to get within ½–1% of your target superfatting.

Oh, and of course none of this actually takes into account the accuracy or variation of those saponification figures.

The other day I was searching for something completely unrelated and came across this amusing video about making Bacon Soap.

The video brought me down memory lane—some years ago we borrowed a book on soapmaking and endeavoured to make soap for Christmas presents. That experiment went wholly wrong and our house smelled like lard for weeks and we had no soap to show for it in the end.

But this video made it look simple and easy, and so on a whim I decided to make soap. I checked for all the ingredients. I had lye, some lard (from my pie crust experiments), some canola and olive oil, and of course water. So I did some research on the web and went to work. A couple hours later, I had soap in the pot waiting to trace (”trace” is a stage the soap gets to, where it’s ready to pour into the mold). It waited… and waited… and finally several hours later (after occasional stirring, I’m not stupid enough to stir constantly for several hours) it did trace and I poured it in. Actually I’m not sure it didn’t trace earlier and I was just looking for something else.

The next day it was set up pretty well in the mold, well on its way to becoming soap. That wasn’t so hard. But I knew it could be easier. So I reformulated, used my imagination (and borrowed some imagination from the web) and tried again yesterday afternoon.

This time I decided to make Castile soap. That is, Olive Oil soap. I didn’t want to make much since it’s just an experiment. I didn’t want to stir a lot. I didn’t want lots of dirty dishes. I didn’t want to mess around with molds. I wanted the whole process to take about 5 minutes. It does. Here are my instructions for making Castile Soap in 5 minutes (and a few weeks of waiting):

Update: now find this recipe at http://hans.fugal.net/soap/castile.txt.

Enjoy your all-natural castile soap. It’s not hard to make, but you may still wonder if it’s worth all the trouble. Allow me to quote:

Hand made soap retains extra glycerin, known to soften the skin naturally. Glycerin is one of the best known humecants (attracts moisture to the skin). It is often extracted during the process of manufacturing commercially made soap, then sold as a valuable by-product. Natural ingredients are rarely used in commercially manufactured soap. If used at all, it is sparingly. One of the best advantages of making your own soap is that you are in charge of quality control. You decide which ingredients to use and how much.

If your skin is sensitive to scents, additives, etc., or you need to impress your wife/girlfriend/soon-to-be-girlfriend, then the benefits are even more pronounced.

The soap you end up with will be the same quailty of soap that sells for $5 a bar at health nut^Wfood stores. It will cost you about $1 and 5 minutes of time to make yourself. If you enjoy making soap, you may want to learn more about the chemistry and how to make different kinds of soaps each with their own qualities and benefits, and how to scent and color them into works of art. The internet is full of great instructions, and you can’t go wrong once you understand the basics, which are well-put by Caveman Chemistry (though to be honest I skipped all that chemistry junk and got to the practical instructions).