KOH purity

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Aug 20, 2019
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Hi! I'm a beginner soapmaker and I'm interested in making liquid soap. The KOH lye I want to use is according to the manufacturer 90-100% pure. That's a 10% difference.. So I'm not sure what percentage to put in the soap calculator?

What will happen if I put a too low percentage?

What will happen if I put a too high percentage?

Would it be okay to put 100% koh purity in soap calc just to be on the safe side but using a recipe with 1% superfat knowing the sf probably will be higher?
Unfortunately, liquid (KOH) soap is more sensitive to the superfat than bar (NaOH) soap. You will need to experiment to see what works best. Speaking for myself as an experienced liquid soap maker, I would first assume the purity is about 95%, create a recipe that should make a clear soap using 2-3% superfat, and make a SMALL batch of the soap.

If the diluted soap is cloudy or separates but does not have excess alkalinity, that would tell me the purity of the KOH is lower than 95%. I'd then choose 90% purity for my next test.

If the soap is clear and does not have excess alkalinity, I would conclude 95% purity is fairly accurate.

If the soap is clear and DOES have excess alkalinity, I would say the KOH has a higher purity than 95%.
More importantly, once you choose your KOH, your water amount for making the lye solution should be 3 X KOH. To accomplish this, go to #3 "Water" and drop down to tick Water:Lye Ratio and type in 3:1.

I'm OCD about clarity, so I use the 90% option and 0% SF, but you can go up to 3% SF ... keeping in mind, of course, that it will leave that % of oils unsaponified. Great in hard bars; can cause clouding in LS. No biggie; just a matter of preference. :)
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