Ohhh DeeAnnnnnaaaaa! Come out and play!

DeeAnna .. my soaping guru, I have a question for you.

If I want to HP a soap and keep one oil from being all eaten by the lye is there a magic number or math formula for knowing how much oil the lye needs "before" adding in the last oil???

I think SAP values have something to do with this but I'm a bit lost.

How does leaving one oil out until the end effect the overall recipe? I understand the idea that leaving one out means it's the superfat but can it effect the way a soap acts?

Do my questions make sense?

IANDA (I Am Not DeeAnna) but I think I can answer this one.

Do your soap calc with all your oils besides the extra fat you want to add at the end. Do a small (or even zero if you're feeling brave) superfat percentage.

Wait until the soap has gone completely through gel phase and doesn't zap/passes your litmus or phenol test and then add the bonus oil at the end.

It's not complicated when you remember that what you're doing is making soap out of oil A (or oil mixture A) and adding oil B as an additive.

Yes, you make perfect sense, MsMolly. And, yes, you're right to think the saponification values are an important part of the answer. There are a couple of ways to handle superfat for hot process.

In your case, I gather you want a certain weight of oils to be turned into soap AND you want a specific different oil to remain unsaponified -- remain as superfat -- in the finished soap. If I'm on track with you, then I'd handle it this way. Bear with me, since I think you already have the general idea, but I don't want to leave room for confusion, so I'll go through all the steps in my thinking --

I'm going to assume you want to make soap using a total of, say, 1000 grams of oils to fit a particular mold. I'm also assuming you want add enough of your special oil to make an 8% superfat.

So the first question to answer: How many grams of oil do you need to set aside to be the superfat? In other words, what is 8% of 1000 grams?

1000 * 0.08 = 80 grams of superfat.

Next question: How many grams of oil need to be turned into soap?

1000 g total - 80 g superfat = 920 grams of soaping oils.

Figure your soap recipe based on the 920 grams of the oils that need to become soap. You don't want these soaping oils to be left over as superfat, so you could choose a zero % superfat for this recipe. I'm personally a little uncomfortable about that because I truly hate making lye-heavy soap, so I might choose a tiny superfat -- maybe 1% -- just to err on the safe side. But something low -- zero or 1% -- whatever you're comfortable with. Keep in mind the superfat will be coming later, so the soap will be skin-safe in the end.

Now you know the correct amounts of NaOH and water that you need to saponify just your soaping oils. Make your HP soap with those soaping oils. When your soap is cooked and tests safe, then add the superfat oil to finish the project.

"...leaving one out means it's the superfat but can it effect the way a soap acts?..."

It could, I suppose. The way most soap recipes are made, the actual superfat is whatever oils are left over after the lye is done "eating". In your case, your separate superfat oil might have characteristics that could affect the soap differently than if this oil were just part of the soaping oils.

To find that out, you'd have to make one recipe with the oils used all together as the soaping oils ... and a second recipe with the special oil added after saponification ... and see how the two versions are different. If you do this, be sure to run the "all together" recipe through a calculator with your desired final superfat (the 8% I used in this example). It is very likely that the lye weight for the "all together" version will be different than the lye weight for the "separate superfat" version.

I hope I've made sense and answered your questions. If not, please let me know, MsMolly....

edit: Songwind and I are singin' the same song!

Thank you both to H-WIND (he-who is not DeeAnna) and DeeAnna. I love both explanations and yes, you both made sense. It's a funky recipe with some expensive oils so I'm afraid to mess around too much but I guess good science will require it. I think I'll do as you suggest and make two batches, one all in and one with special oil as superfat.

I read a great tutorial, which I can't find at the moment, but it told how to figure how much oil even more precisely, depending on how precise you want to be, taking into account the SAP values of a given oil. For example, 8% SF with Monoi oil will be much different than 8% SF with Jojoba oil.

Like DeeAnna mentioned above, figure your recipe without the SF oil figured in, at a low or 0% SF. (I use 1% to be on the safe side)

Write down that lye amount.

Now, if you want a SF of 8%, then you would take 1 minus 8%, so .92, and divide your lye amount by that. (This gives you the lye amount to completely saponify your original recipe plus a SF amount, but you're not doing that, so don't worry) ( 1-.08=.92 and 4.07/.92=4.42)

So now you have a larger lye number and your original smaller lye number, right?
Subtract the smaller number from the larger one.

So say it took 4.07oz lye for my 1% SF recipe. And I do 8% SF. Then the larger number would be 4.42. So the difference is .35 (4.42-4.07=.35)

Now go on soapcalc and check the SAP of whichever oil you want to use. For Monoi, it's .182 and for Jojoba it's .066

Take that number you subtracted above, the .35 in our example, and divide it by the SAP. This will tell you the exact amount of that specific oil to use to achieve your SF (.35/.182=.52 or .35/.066=5.3)

For Monoi, it would be 0.52oz. For Jojoba, however, it would be a whopping 5.30 oz to achieve the same SF percent!!!

Obviously, this can make a big difference in both the feel of the soap, and in your pocketbook!

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Summary:

1) Figure your recipe with low SF and write down that lye number. (4.07)

2) Decide a SF percent, and subtract it from 1 to get a decimal percent left. (1-.08=.92)

3) Divide your lye amount by that decimal number. (4.07 divided by .92=4.42)

4) Subtract the two numbers. (4.42-4.07=.35)

I always write this number on my recipe page, as I use the same numbers all the time for the rest of the recipe, and then only just change up my SF.

5) Divide this little number by the SAP value for the oil you want. (.35 divided by .182=.52oz monoi)
This will give the amount of SF oil to use after cooking your recipe.

Don't forget to actually ADD it to the batch. (I have done that lol -- got it in the mold, went to clean up, and realized there was a little dish of oil still sitting there... oops)


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Actually, the tutorial I saw was more in an equation form, which I have broken down a bit further, so I hope I made it easy to understand? It's 5 steps, and if you just follow them one at a time, you will get the math right.

For me anyhow, it makes it super-easy to change up a HP recipe just by altering the SF I add afterwards.

PS: You can double-check your numbers in soapcalc by plugging in your numbers including the SF, and they should match up at the desired SF % (the smaller number) and also at the 0% or 1% or whatever (the larger number)

You raise a good point, GrayceWorks. I think your method is mathematically more correct. Here are the links you were wondering about:

http://curious-soapmaker.com/superfat-vs-lye-discount.html
and
http://curious-soapmaker.com/how-to-calculate-the-hot-process-superfat.html

Yes!!! That's the one. Thank you!

Question for you, since you seem to be better at numbers than I am though,

Why on my calculator, does 4.07 / .92 come out .03 higher than 4.07 + 8% ??? Granted, in ounces it's not a huge deal, but it bugs me. They should be the same, right? I'm sure there's some reasonable explanation...

I just stick with dividing by the decimal place instead, for consistency.

grayceworks said:

I hope I made it easy to understand? It's 5 steps, and if you just follow them one at a time, you will get the math right.

Click to expand...

THANKS!! I think *gulp* .. it will take reading that a few times to make easy sense of it but I do appreciate it.

I played with it for a few hours over and over until it stuck in my head. I figured I'd better get it down, since I seem to prefer HP, and I want to be able to use SF without destroying the special oils I want to play with. And I want to know that it's exactly how I want it to be, not what the lye decides it will be lol.

Follow the summary part I outlined. Above that is all the explanations for the steps, but just follow the summary steps one at a time.

Smaller explanation:
get your lye amount, get the percent of SF and convert to decimal, divide by the decimal for the SF, subtract the two numbers, divide the result by the oil SAP.

Kinda like learning to use soapcalc at first. I spent hours and hours with that until I figured it out thoroughly. Hmm. I still spend hours and hours with it though.... Come to think of it... I have a recipe idea.... hmm

PS - I'd be happy to double-check numbers for ya if you want to try it.

"...Why on my calculator, does 4.07 / .92 come out .03 higher than 4.07 + 8% ???..."

I'll show you the same equations rewritten so they look more similar to each other:

First one: 4.07 / ( 1 - 0.08 )

Second one: 4.07 * ( 1 + 0.08 )

Can you see the difference now?

If the saponification value for all of the oils was a constant number, Songwind's and my method and the Curious Soapmaker's (CS) method would give you the same numbers. But sap values can be quite different for the different oils in a recipe, and the CS's method accounts for this difference, whereas S&D's method does not.

I am following the math (inst and amongst breaks from work), but I have not yet come up with a really good way to explain it at the moment. Sometimes DOING the math and EXPLAINING the math are quite different critters, and I'm drawing a bit of a blank on this one at the moment.

Give me a bit to digest -- or does someone else have a good explanation to share? I'm certain I'm not the only geek in the group! :crazy:

Yeah, that's why I was using CS's method for calculating for specific oils for after the cook, since I do a LOT of HP soaping.

I just couldn't figure out why it was divided by 1-.xx instead of adding the percent, but the actual difference in the final value is so negligible it doesn't matter except that I WANT TO KNOW. lol It only makes about a tenth of a gram difference in the outcome of the final calculation though. lol

Here's a no-math way to do CS's method of figuring superfat added after the HP cook.

1. Figure out the oils you want to use in your basic recipe. CS uses this example in her tutorials (see links above), so I'm going to do likewise:

Palm 4.8 oz (soaping fat)
CO 4.8 oz (soaping fat)
Olive 11.2 oz (soaping fat)
Superfat at 10% with shea butter -- this is the "special oil" that will not be turned into soap.

2. Go to soapcalc (or your favorite soap recipe calc) armed with your recipe.

3. Enter the soaping fats into SoapCalc. In this example, that would be the weights of the palm, CO, and olive.

4. Set the superfat at zero (or whatever minimum you're comfortable with).

5. Calculate the lye weight and write it down. This is the lye you will use in your recipe -- it is the amount of lye that will saponify all of your soaping fats. In this palm-CO-olive-shea example, SoapCalc says the amount of lye needed is 3.078 ounces.

6. Next figure how much superfatting oil is needed to give the right amount of superfat. First step is to change the superfat to the % you really want -- that would be 10% in this example.

7. Add the superfat oil (that would be shea in this example) to your ingredients list and guess a reasonable weight.

What's a good guess? Well, the superfat is supposed to be 10% so let's try that. We've got 20.8 ounces of fats so far (4.8 + 4.8 + 11.2 = 20.8 ounces), so I'm going to make a first guess of about 10% of the oil weight (20.8 * 0.10 = 2.08 ounces). Enter 2.08 ounces of shea into the recipe and calculate. If you're following along in SoapCalc, you should see an answer of 3.009 ounces of lye for an added 2.08 ounces of shea. Not good enough! We want the recipe to use 3.078 ounces of lye so all of the soaping oils ... and just the soaping oils ... are saponified.

So let's make another guess -- try 2.5 ounces of shea and recalculate the recipe. SoapCalc comes back with 3.057 ounces of lye. Need More Shea! So let's raise the shea to 2.8 ounces and recalculate.

SoapCalc says 3.092 oz lye. Too much! Back off the shea a bit. Check again. Continue to tweak the shea weight until SoapCalc says the lye is 3.078 ounces or as close as you can come to that. Hint: Try 2.67 ounces shea. SoapCalc will return an answer of 3.077 ounces of lye. 2.67 oz of shea is also CS's answer for this example. Good enough!

8. Summarize your recipe. The example recipe I've been doing here would look like this:

Palm 4.8 oz
CO 4.8 oz
Olive 11.2 oz
Lye 3.078 oz
Water ??? oz based on your preferences
Shea 2.67 oz to be added after the cook
Superfat 10%

****

Here's another recipe to try if you want to practice either the SoapCalc trial and error method or SC's math-based method. You should get the same answer either way. This is a horrible recipe, by the way, but I've chosen these fats because their saponification values vary a lot.

Coconut oil 200 g (soaping fat)
Lard 200 g (soaping fat)
Olive 200 g (soaping fat)
Superfat at 8% with meadowfoam seed oil

To help get you started, SoapCalc tells me the lye needed to saponify just the soaping fats at zero superfat is 91.979 grams. Is that what you get? See what you come up with for grams of meadowfoam superfat! An answer to the nearest 0.1 gram will be plenty good.

****

DeeAnna said:

To help get you started, SoapCalc tells me the lye needed to saponify just the soaping fats at zero superfat is 91.979 grams. Is that what you get? See what you come up with for grams of meadowfoam superfat! An answer to the nearest 0.1 gram will be plenty good.

Click to expand...

That's what I got and for Meadowfoam I got 66.3 grams. I'm following along physically but not really sure if I'm following along mentally.

PERFECT! WHooooo, girl, you did it!

I understand the problem of feeling foggy about this. It's not a neat, tidy, straightforward problem to solve -- even I missed the point until Grayce steered us back in the right direction. Either a fair bit of algebra or a fair bit of trial and error.

DeeAnna said:

I understand the problem of feeling foggy about this. It's not a neat, tidy, straightforward problem to solve

Click to expand...

Yes, and I'm struggling with wanting to know more. It's like driving a car, I can know how to drive but I also need to know the rules of the road. In this case I'm driving but don't understand the rules of the road yet.

And a big thank you to Grayceworks for helping with this.

Did either of you take further education that's helping with all this? I have a college education but sadly dropped out of Chem class in high school. It's coming back to bite me in the arse now. I'm learning all I can about soap through reading but if there were science classes that would help I'd be signing up pronto.

Never took chemistry at all. I did Physics freshman year, then took my GED and started graphic design school. So I'm sure I missed out on some stuff... I am loving DeeAnna's chemistry explanations!

My education in soaping has been books, online, youtube, and here on SMF, and of course, trial and error.

Sometimes you just have to follow the steps over and over and suddenly the reasons for the steps will click and make sense.

When I was doing that math over and over to get it in my head, I actually was using the method DeeAnna just outlined to double-check my math, going in and plugging my results into soapcalc and seeing if it came up with the same lye amount for that amount of SF oils. But mostly I just kept memorizing the math until I understood it. And I didn't understand it fully until I'd made a few batches and kept calculating and recalculating.

Then it clicked, I was just taking the difference in lye amounts needed for a 1% SF and whichever SF percent I wanted, and dividing that by the SAP for the oil I wanted to use, to get the amount of oil.

I still have it written on the inside cover of my recipe book though, so I can make sure I don't miss any numbers when I'm calculating for a new recipe. All my existing recipes, I wrote down the final amounts for all my favorite SF oils. I also made a page listing all the SAP values for my favorite oils so I don't have to keep referring back to soapcalc over and over which is a pain on my little tablet. lol

Um, well, I have graduate degrees in engineering -- so, yes, lots of chemistry, physics, and math. I also taught math and science at our local community college for 10 years. The teaching experience is probably more help to me on SMF. Being able to explain math and science clearly is quite different than being able to do the math and science well.

What I know to be true for me is that having a project (such as soap making!) is a strong incentive to learn more about science, algebra, or even calculus. Math and science are far too abstract for many people ... until they take on a project they want to do well. Suddenly the math or science starts to seem useful and the person finds a reason to learn. For example, I had to take a year and a half of calculus as an undergrad. Got fine grades, but I just learned it in the abstract and I didn't have a reason to really use it and "get" it. Fast forward 15 years to grad school and a really interesting class (to me, at least!) about water flow in underground aquifers. Calculus required! Because I was interested, I dug into re-learning calculus and realized it was could be really useful.

Sleeping on this was helpful. I'm writing an detailed answer that I hope will give more perspective on the whys and wherefores of this problem we're talking about. Should be done later today, and I'll post it in this thread. More laterz!

MzMolly65 said:

Yes, and I'm struggling with wanting to know more. It's like driving a car, I can know how to drive but I also need to know the rules of the road. In this case I'm driving but don't understand the rules of the road yet.

Click to expand...

I learned to drive in fields for work at a barn before I was 15/16. When I was learning how to drive on the road I said something about already knowing how to drive, and my dad said "you know how to operate a car. You don't know how to drive yet." And I've always really liked that analogy, and have even morphed a bit to use with teaching riding lessons.

Lin said:

I learned to drive in fields for work at a barn

Click to expand...

That's where I learned to drive .. farm kid during hay season and all that. Then I moved out and went to the big city .. OMG .. I did NOT know how to drive at all.

That's how I feel with this particular soap math/question. I'm making soap but I definitely don't know how to MAKE SOAP!

I'm trying to understand why the required lye weight would go down when the superfat oil is added into the calculator? and why do we need to do that calculation at all? Why not just do the calc on the oils we want to saponify and add the superfat in at the end without fussing with the lye?

My head says .. if I just add the oil in at the end without adjusting the lye the way we are, my soap will be a greasy mess .. am I correct on that much?