Superfatting questions

[narnia]

There are a couple of different ways that people do it......

One way that some do it is to type your recipe (without your super-fat oil) into SoapCalc at 0% super-fat, hit the view/print button, then jot down the lye amount it gives you. ....

Next, go back to page 1 on Soapcalc (where all of your original recipe amounts should still be), and change the super-fat % to whatever % you want it to be for your finished soap.....

Then choose what fat you'd like to super-fat with and add it to ingredient list, and then type in a random amount for it, like 2 oz or whatever (it really doesn't matter at this point)......

Next, hit view/print and look at the lye amount it gives you. Does it match the amount you jotted down earlier? It may or may not. If it's lower, go back to page 1 and increase the amount of your super-fatting oil until the lye amount on page 2 matches the amount you had jotted down. Or if it is higher, reduce the amount of super-fatting oil until the lye amounts match. That will tell you how much super-fat to add.

Another way that people calculate the superfat (which is more accurate, actually) is discussed here: http://curious-soapmaker.com/superfat-vs-lye-discount.html


IrishLass

Thank you! I had read that article, but it made my head swim!! I think I will try the lyecalc method that you gave.

I read one article where a soaper said that she added a tablespoon of sf oil per pound of oil after cook. I don't know what %sf that would amount to...she did not say...

 

[topofmurrayhill]

Thank you! I had read that article, but it made my head swim!!

It should make your head swim, because it's silly.

(1) Put your non-superfat oils in Soapcalc with a 0% lye discount. Let's say they weigh 950 g. Make that.

(2) Calculate a 5% superfat as (950 / (1 - .05)) - 950 = 50 g superfat oil. Add that.

That's all there is to it. Replace 950 with your own oil weight. Replace .05 with your own superfat percentage.
Here is the extra credit part. Why is that the way to do it, while the article is needlessly obsessive and confusing?

Because we have a definition of superfat in CP soaping that doesn't need to change for HP. The definition is:

The percentage of total oil weight that remains unsaponified.

The method I described above is correct based on that definition.

By using that definition of superfat in CP, we are also using this:

List of Things We Don't Care About

(1) The number of MOLECULES of oil that remain unsaponified, which will vary with the exact oils we are using.

(2) The proportion of superfat weight versus total product weight, which will vary with the oils we are using.

When the article says that saponifying 95% of (950 g OO + 50 g CO) does not produce the same result as saponifying 100% of 950 g OO and then adding 50 g CO, that is true. Please see List of Things We Don't Care About above.

 

[narnia]

It should make your head swim, because it's silly.

(1) Put your non-superfat oils in Soapcalc with a 0% lye discount. Let's say they weigh 950 g. Make that.

(2) Calculate a 5% superfat as 950 - (950 / (1 - .05)) = 50 g superfat oil. Add that.

That's all there is to it. Replace 950 with your own oil weight. Replace .05 with your own superfat percentage.

Let me see if I got this right...

If I want to make 28 oz of soap with 10% sf added after cook:
28 - (28 / 1 -.1) = 28 - (28 / .9) = 28-31.11 = - 3.11

I got a negative number. Should I turn that into a positive number? Is that the amount that I should add to sf?

I did feel that the article was too meticulous for my level of soaping...

 

[topofmurrayhill]

Let me see if I got this right...

If I want to make 28 oz of soap with 10% sf added after cook:
28 - (28 / 1 -.1) = 28 - (28 / .9) = 28-31.11 = - 3.11

I got a negative number. Should I turn that into a positive number? Is that the amount that I should add to sf?

I did feel that the article was too meticulous for my level of soaping...

It is too meticulous for any level of soaping. It's not any more right than what I showed you, which is at least consistent with how we normally think of it.

Sorry for the brain seizure. I wrote it backwards, now corrected. But yes, you can just make it positive.

That brings the total oil amount to 31.11. Your superfat is 3.11 which is 3.11 / 31.11 = 10%.

 

[dixiedragon]

So...much...math. *brainsplode*

 

[narnia]

So... if I don't want to increase my oil quantity but wanted to keep it at 28 oz with 10% sf, would it look like this?

28- 28(.10)= 28-2.8= 25.2

25.2 oz of oils with 0% sf in lyecalc and then add 2.8 oz superfat after the cook?

 

[topofmurrayhill]

So... if I don't want to increase my oil quantity but wanted to keep it at 28 oz with 10% sf, would it look like this?

28- 28(.10)= 28-2.8= 25.2

25.2 oz of oils with 0% sf in lyecalc and then add 2.8 oz superfat after the cook?

Yes that's right.

 

[The Efficacious Gentleman]

I do a bit like the method IL posted, but to do the leg work for the method ToMH posted -

Make your full amount recipe in soap calc, including the SF set up correctly for your needs, batch size where you want it and hit calculate.

Make sure the recipe calculation is set to weight mode (soapcalc does this, not sure about the others) and remove your superfat oil. Set the SF % to 0 and then hit calculate.

You now have the recipe with the lye and water to make a batch that is 0% SF with enough space left over to add in your SF after the cook.