Utah Open Source Planet

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.

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.

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.

Previously on The Fugue, I told you how to make Castile Soap in 5 Minutes. Having been through the process a few more times since then, I have a couple of addendums.

First, on measurements. If you're at all serious about making soap you either need to do large batches or get a scale with 1 gram precision. With my old scale (which had 5 gram precision) I had hits and misses with the size of batch that I like. i.e. 1–2 bars worth. Most recipes you find on the internet are what I would deem "large batches", and are really more like medium batches. But when you're trying to nail down the perfect recipe, making 5–10 bars of soap is wasteful, or at least a really really slow way to go about it.

Second, on ingredients. Pure castile soap is great, but has to be treated with respect or it can get really slimy. Coconut Oil is easy to obtain and adds hardness and lather. Lard or tallow is cheap and also hardens the bar. So I've been doing 6 parts olive, 2–3 parts tallow or lard, and 1–2 parts coconut oil and others (like cocoa butter). I calculate the lye then use 2 parts liquid for 1 part lye (by volume). I like to use milk instead of water, because I made this one bar with milk and the caramelized sugars (from the lye heating up when mixed with the milk) made a bar that smelled divine.

Third, on measuring again. For the size of batch I'm doing (on the order of 80 grams fat) I figured out that measurement error gives me ±2%. So I round the lye and fats (check the total weight so the measurement errors don't compound), then add 2g (a bit over 2%) of fat. So I know I'm between just under 1% superfat and 5% superfat, which is acceptable. I don't want more than 5% but of course you really don't want less than 0%. The same idea would apply with a 5g precision scale, but you'd have to be doing batches about 5 times as large (I think).

Fourth, on temperature. I don't measure temperatures. I aim for "warm to the touch" on the outside of each container before bringing them together. Rather than wait for the lye to cool down to "warm", I start with really cold liquid, sometimes in the form of one or two ice cubes. The ice cubes melt, and the final temperature is much closer to the target and so there's much less waiting. Obviously, if you're using more solid fats you want the temperature to be above their melting points until you get a good mixture.

Which brings us to the final point, mixing and molding. I am more than ever convinced that shaking in a water bottle (or large soda bottle) is an excellent way to go. It is safe, convenient, cheap, and fast. However, it's not such a great mold. It will work as a mold, but it will take that much longer to set up (evaporate water). Usually you demold after 1–2 days, but getting cheese-consistency soap out of a water bottle without marring it is an exercise in futility. So now I use paper cups as molds, and I pour the soap in from the water bottle when it reaches trace. As a bonus, you can clean out the water bottle and use it again the next time. It's easy to extract the soap from the paper cups, and they're cheap and nice and round.

So here's an updated base recipe. Go forth and wash!

Ok, so I'm catching up on a backlog of photos I've been meaning to post. How did you guess?

Here are some photos of me rendering tallow. I went to Albertson's and asked the butcher folk for some beef fat. They said come back later and they'd save me some. I did, and I came home with a couple pounds of fat. I cut it into cubes and put it in my dutch oven

then stuck it in the oven at 225°F for awhile. Nothing really happened. A little melting. This could take all day. So I put it on the range top and added water and brought the mess to a boil. I let it boil for awhile. It smelled about like boiling stock, if you can imagine that. After awhile, I declared the low-hanging fat picked, and poured the liquid through a collander into a receptacle which I put in the fridge after it cooled off somewhat. The next day I poured off the water. Et voilá! Tallow.

I made one bar of soap with it (and olive oil and coconut oil and a couple drops of pine essential oil), and though it hasn't yet fully cured and I haven't truly used it yet, it does smell a bit like beef fat. Or that might be my imagination. So I simmered it again in fresh water for about 4 hours, then refrigerated. This time it was a bit whiter. I made another bar, with basically the same ingredients (sans pine essential oil) but also with a bit of cocoa butter. Again, I haven't truly used it yet, but it seems to smell better.

If I do it again (and I may, if I like the soap), I'll do a larger batch, and I'll do some things different. First, I'll ask them to grind it for me. Hopefully more surface area will mean faster melting. Then, I'll first cook it dry on low heat for a time, kind of like cooking bacon. Or perhaps in the oven at a bit higher temperature. When I reach the "low-hanging fat" point, I'll pour it off into some simmering water and simmer it for a couple of hours. I'll let that harden, and simmer it for a couple of hours again. If I'm in no hurry, I'll do it a third time. Then I'll have lot's o' tallow that I'm confident is nice and pure.

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):

Castile Soap

15 g lye (NaOH) ±1g
50 ml cold water
115 g light olive oil ±3g
plastic water bottle

WARNING: lye is dangerous. Heed the warnings on the label. Use gloves,
protective clothing, and eye protection. Don't breathe the fumes. Don't use
aluminum utensils or containers.

Measure the lye and oil very carefully.

Put the olive oil in the water bottle. Put the water in a pyrex measuring
cup.  Slowly pour lye into water. Stir until clear. Pour lye+water mixture
into bottle with olive oil, and replace the cap securely. Observe that the
water and oil separates like Italian salad dressing. Shake vigorously until
the mixture becomes white and creamy (a couple of minutes). Periodically
check for separation and shake again.

Once it has stopped separating, your work is done. This is called "trace".
It may happen right away, or it may take a couple of hours or even days of
intermittent shaking, depending on many factors. But if you weighed the
ingredients carefully it will happen.  Set it aside, out of the reach of
children, for 4 days. Then cut the plastic bottle and cure the soap in a
dry place for 2-4 weeks.

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).