More Citric Acid questions...


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Aug 5, 2014
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Eastern Canada
I want to try out citric acid for both solid and liquid soaps.
There have been many thread, here is one:

I use Soapmaker 3 so what I'd like to do is enter Citric Acid as an oil and allow the program to calculate the lye amount. Quite frankly I don't trust my math or
science skills...

This is what I've found for SAP values:
SAP value is 0.571 for monohydrate citric acid.
SAP value is 0.625 for anhydrous citric acid.
(nubers come from this post-

So my question is, do these sound like appropriate values?

Also, monohydrate vs anhydrous... I didn't even know there was a difference to tell you the truth. Mine is not labeled as either. I assume I have monohydrate. It's the crystallized stuff that you use in bath bombs.

My Google-Fu tells me "monohydrate forms when citric acid is crystallized from cold water"

TIA to all of you sciencey types out there that have a moment to answer!


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Sep 19, 2011
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Southern California
I use citric acid in all soap and use .624 to configure my extra lye needed. I don't use soapmaker 3 for my recipes, only for storing my recipes, but just multiply it myself. The info for the .624 extra lye was per DeeAnna in another thread.


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Feb 20, 2013
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The bottom line is you will never really know unless you take the time to heat the citric acid powder to convert the hydrate to the anhydrous. Or unless you buy reagent grade citric acid meant for lab use.

Given the small amount of citric acid being used in a typical soap recipe, it doesn't make a great deal of difference which one you have anyways. You would be off one way or the other by no more than a gram or so in a recipe for 1000 g of fats.

There is far more error built into most soap recipes because most soap calcs assume NaOH is 100% pure, rather than a more realistic 95% purity or even less. So if your citric acid calculation is a wee bit off, the error is a very small matter.

Bottom line -- Pick whichever poison you prefer, and you'll be fine.

FWIW, the advice I always give is based on anhydrous citric acid -- 10 g citric acid neutralizes 6.24 g NaOH and 10 g citric acid neutralizes 8.42 g KOH.

And FWIW, it's not a "sap value" even if SM3 calls it that, because citric acid doesn't saponify. But that is just the chemistry geek in me niggling about the terminology. :)
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