Recipe calculation by hand (Dual Alkali with vinegar)

[ngian]

Hello everyone

On my latest soap that I made I wanted to use new methods in order to make it and that involves making all the calculations with a pencil and a paper, making a dual alkali soap, and using a full water replacement with vinegar. A while ago topofmurrayhill has posted the "manual" way of calculating ingredients for a recipe without the need of an electronic soap recipe calculator and also how to calculate the excess lye needed for the vinegar in a recipe. Also DeeAnna has shown us how to correct the amount of alkalies really needed in order to make an actual lye discount, eliminating the hidden one found inside the alkali.

I would like to write all these steps once more in one place along with dual alkali calculations that I did on my latest recipe. It is really easy to do them by hand and I feel that someone gains even more control in the entire soaping process.

The only thing we need to know is the SAP value of each oil that our recipe will have. My recipe had

75% Olive Oil (with very low acidity) (600gr)
20% Palm oil and (160gr)
5% Castor oil (40gr)

This recipe could also be named as the no coconut oil soap as I was trying to have bubbles from the addition of the 10% KOH alkali.

So let's start:

1) Calculation of the saponification
The first step to do is to find the quantities of the alkalies needed to saponify our oils based on their SAP values for both NaOH and KOH:

Olive oil: 600 g (SAP - NaOH: 0.135 | KOH: 0.19)
Grams alkali needed for its saponification:
600 x 0,135 = 81gr NaOH
600 x 0,19 = 114gr KOH

Palm oil: 160 g (SAP - NaOH: 0.142 | KOH: 0,199)
Grams alkali needed for its saponification:
160 x 0,142 = 22,72gr NaOH
160 x 0,199 = 31,84gr KOH

Castor oil: 40 g (SAP - NaOH: 0.128 | KOH: 0.18)
Grams alkali needed for its saponification:
40 x 0,128 = 5,12gr NaOH
40 x 0,18 = 7,2gr KOH

So if we sum all grams of soda (NaOH) and all the grams of potash (KOH) will have the total weight of the respective alkalies needed to saponify the oils:

Saponification of all oils only with NaOH: 108,84gr
Saponification of all oil only with KOH: 153,04gr

These weights however are for 100% purity, which is not so in reality. According to the Certification of Analysis documents that the supplier gave me, the NaOH I have in my hands is 98% pure and the KOH is 85% pure, if I store them airtight after opening them and I no further decrease their purity with their exposure to the atmosphere. So the correction of purity is the next step:

2) Correction of the alkali weight needed based on their actual purity

Corrected alkali weight = amount of alkali we calculated above x (100% purity / purity of the alkali that we have in our hands)

NaOH = 108,84 x (100/98) => 108,84 x 1,02 => 111gr
KOH = 153,04 x (100/85) => 153,04 x 1,17 => 179gr

So these weights are what we need to make a soap with an almost real 0% lye discount (I'm writing "almost" as I don't know the real SAP number of the oils I have in hand).

3) Ratio of each alkali in the recipe
The next step is to calculate the weights of each alkali we will use depending on their percentage use in the recipe. In this I decided to use 90% NaOH and 10% KOH, so we will do the following multiplications based on the latest grams of ​​alkalies we found above:

Using NaOH 90%: 111gr x 0,90 = 100g
(If we wanted to use it 95% NaOH in the recipe, we would multiply by 0.95).

Using 10% KOH: 179gr x 0,10 = 17,9gr
(For example if we wanted to use 5% KOH in the recipe, we would multiply by 0.05).

4) Lye discount by 3%
The next step is to calculate the weights of alkali we found above with 3% discount (or as much discount you usually do in your soaps) in both NaOH & KOH:

NaOH discount of 3%, 100g x 0,97 = 97gr
KOH discount of 3%: 17,9gr x 0,97 = 17,3gr

(For example if we wanted to make NaOH / KOH discount of 6% in the recipe then you multiply by 0.94)

5) Calculation of water
After calculating all the alkalies needed for our recipe then we can calculate the water needed based on them. The lye concentration that I will use will be 1,7: 1 (37% lye concentration) which practically means that the amount of water is the weight of the alkali multiplied by 1,7. So according to the latest amounts we got at step 4 we have:

Water needed for NaOH: 97 x 1,7 = 165gr
Water needed for KOH: 17,3 x 1,7 = 30gr

So we will need a total of 165 + 30 = 195gr distilled water to dissolve the alkalies.

But as I said initially, I will use vinegar instead of water in the recipe, to take advantage of the acetic acid that will offer hardness similar to salt. And thus we should still make one more correction in the amount of the alkalies needed so as for them to react with acetic acid without raising further the recipe's lye discount:


6) Alkalies correction due to vinegar
So if you still read me without changing the page in order to read something less boring, we're going to see how to calculate NaOH & KOH we will need to keep the original alkali 3% discount to the recipe.

The vinegar that we have in Greek market is 6% acidity (it is written on its label) and it means that 6% of its weight is acetic acid. The alkalies that are needed to fully react with 1gr of acetic acid is 0,66gr NaOH and 0,92gr KOH respectively. So for the "water" we calculated above we must do the following:

Acetic acid present in vinegar for NaOH: 165gr x 0,06 (6%) = 10g
Additional NaOH needed for the acetic acid: 10 x 0,66 = 6.6 g NaOH

Acetic acid present in vinegar for KOH: 30g x 0,06 (6%) = 1.8 g
Additional KOH needed for the acetic acid: 1,8 x 0,92 = 1.6 g KOH

Corrected NaOH because of vinegar: 97 + 6.6 = 103,6gr
Corrected KOH because of vinegar: 17.3 + 1.6 = 18,9gr

Thus, after all of the six steps above we have:

Olive oil: 600gr
Palm oil: 160gr
Castor oil: 40gr

NaOH: 103,6gr in 165gr of vinegar
KOH: 18,9gr in 30gr of vinegar

The dissolution of the two alkalies can be done in the same vessel with 195gr of vinegar for simplicity. You can follow any steps that you might need for your recipe and any of them that you feel comfortable with (eg. step 2)

If you managed to read me until here, congratulations!

I also used 3% of French Green Clay and Masticha/Sandalwood EOs. In my soap I forgot to calculate the 6) step and as a result I made the soap with almost 10% alkalies discount. The soap seems perfectly hard (I think that acetic acid makes a "better" hardness compared to sodium chloride, along with 37% lye concentration), it is a bit oily in its surface, and as I was cutting it 9 hours after I mold it and CPOP it for 1 hour, it was really hard to cut.

My next project will be to make it once more but with the calculation of the 6) step along with changing the ratio to 85% NaOH and 15% KOH. Vinegar and water discount is something that I like lately in soaps.

 

[Scooter]

That looks great!

Scooter

6) Alkalies correction due to vinegar
So if you still read me without changing the page and read something less boring, we're going to see how to calculate and NaOH & KOH we will need to keep the original alkali 3% discount to the recipe.

This is not boring at all. By the way, this answers a question I had just posted in another thread--that is, does anyone see any value in using a small bit of KOH in any kind of soap besides 100% OO soap.

I do have a question about the vinegar. Why add it? What does that do for the soap?

Thanks!

Scooter

 

[earlene]

This is not boring at all. By the way, this answers a question I had just posted in another thread--that is, does anyone see any value in using a small bit of KOH in any kind of soap besides 100% OO soap.

I do have a question about the vinegar. Why add it? What does that do for the soap?

Thanks!

Scooter

I have started using vinegar in place of some of the water in my lye solution. It tends to make a harder bar of soap. Thanks to TeresaT, who did a whole 1:1 tutorial with me when we were at SoapCon2016!

It's really pretty interesting and there are a lot of threads addressing the use of vinegar in soap here at SMF.

Here's a pretty interesting one started by topofmurrayhill: http://www.soapmakingforum.com/showthread.php?t=57991

Another one by topofmurrayhill:
http://www.soapmakingforum.com/showthread.php?t=59295

TeresaT started this one about making ACV soap: http://www.soapmakingforum.com/showthread.php?t=59092

Here's an older one from 2009 about ACV soap (member new12soap):
http://www.soapmakingforum.com/showthread.php?t=42734

There are more.

ngian, thank you for reporting in detail on your experiment. I am really interested in the results using a higher KOH percentage. I tried it only once above 5% and didn't like the result. But now I am thinking I should try again and that one time it was something else that was the problem. I thought the soap was too soft, but I'd have to search my notes to find which soap that was and what other factors may have impacted the result.

 

[Scooter]

Thanks for all the links and tips/advice! I appreciate it.

Scooter

I have started using vinegar in place of some of the water in my lye solution. It tends to make a harder bar of soap. Thanks to TeresaT, who did a whole 1:1 tutorial with me when we were at SoapCon2016!

It's really pretty interesting and there are a lot of threads addressing the use of vinegar in soap here at SMF.

Here's a pretty interesting one started by topofmurrayhill: http://www.soapmakingforum.com/showthread.php?t=57991

Another one by topofmurrayhill:
http://www.soapmakingforum.com/showthread.php?t=59295

TeresaT started this one about making ACV soap: http://www.soapmakingforum.com/showthread.php?t=59092

Here's an older one from 2009 about ACV soap (member new12soap):
http://www.soapmakingforum.com/showthread.php?t=42734

There are more.

 

[topofmurrayhill]

Wow, nice job.

The only thing I would critique is the adjustments for purity. I believe this approach has been promoted erroneously. Unless you do an assay of your caustic potash, you can't know much about it's purity.

First, I think it's a little risky to suggest that people get the purity of the KOH from their supplier. Some suppliers don't know enough to give the correct answer. People have been given the purity in terms of dry matter -- ignoring the moisture -- and have used values like 99%, which can contribute a huge unanticipated lye discount.

Even if they have a supplier like yours who knows the type of KOH he is selling, you can't use 85% because that is a minimum. So it's quite possible if not likely that you are calculating a lye excess. The potential error in this case is generally in the direction of using too much KOH, which is the opposite of what we normally want. We like to err on the conservative side, especially when guiding new people.

Of course, in the case of KOH you do have to assume something, so what to do? The alternatives are illustrated by two popular lye calculators. Summerbee assumes 95%, which is the most conservative option because that is pretty much the maximum the caustic strength might be. Soapcalc gives you the 90% option, which helps avoid an excess superfat by choosing a reasonable number that is probably not too far off the mark. I go for the 90% option myself.

Testing the KOH yourself is of course an option, but practically nobody will do that.

 

[ngian]

You are right TOMH, instead of writing "according to the supplier" I should have written "according to the Certification of analysis document that came with the alkalies" as this is what I really did. I should edit my initial post at this point.

For the record (as you may already know and remember) I have also tested myself the purity of both alkalies with the method I have posted before ( http://www.soapmakingforum.com/showthread.php?t=60535) , and they were really similar with the values in their coa documents.

 

[topofmurrayhill]

You are right TOMH, instead of writing "according to the supplier" I should have written "according to the Certification of analysis document that came with the alkalies" as this is what I really did. I should edit my initial post at this point.

For the record (as you may already know and remember) I have also tested myself the purity of both alkalies with the method I have posted before ( http://www.soapmakingforum.com/showthread.php?t=60535) , and they were really similar with the values in their coa documents.

That makes sense, and I had forgotten.

FWIW, I would emphasize the more practical instructions as being the standard approach, since a lot of people won't be able to get a COA or perform the quick titration method effectively. We don't want them to proceed based on inaccurate information, thinking that they are being more exact.

For those who want to try testing their KOH, I think there's a bit of an issue in some of the instructions regarding weighing. There are a number of sources of error in the procedure, so you don't want a significant contribution from weighing error. I wouldn't recommend depending on the quick titration technique unless you have a centigram scale.

To use the scale, you should see the original Dunn video to understand how to correctly weigh FROM the scale instead of ONTO it. A good centigram scale with a big enough capacity to weigh onto the scale for this procedure can be very expensive. Weighing from the scale makes it much easier not to overshoot when adding the alkali, and since you don't need much capacity to handle the CA and KOH, you can put a few extra bucks towards quality instead of capacity.

 

[Steve85569]

This post should be made into a sticky.
I may just " have to" use this to set up a new lye calculating spreadsheet this winter.
My outside projects are covered in white stuff.

 

[Seawolfe]

Wow those calcs all in one place are invaluable. +1 vote for sticky.

And can I just say that those soaps are SO pretty. I adore French green clay. I want them!