Lye quality question

[Sapwn]

I used to buy lye for 3.40euros a kgr from the same shop every time. A few days ago I found it in another shop for 2.20 euros a kgr.


In the first shop yhey describr it as 99% pure while in the second they say nothing.


Are all lyes yhe same?
The answer should be "yes" because soap calculatores behave as if it is only one kind of NaOH and not many.


Would you consider the cheaper one less pure?

What should I do with the cheap one when using it in a recipe of soap calc?

 

[Ruthie]

I am always looking out for a bargain, but if the label does not say anything, I would be suspicious. Is there any way to check out the cheaper brand? Have you looked online for information about it?

ETA: if it does not say anything, it would be impossible to know what to do, or even if you should use it.

 

[dagmar88]

Are all lyes yhe same?

No; there's different strengths and grades.
I'd suggest you get the one with the least impurities.
I only use food grade NaOH; but food grade KOH is about €50 per kilo.

 

[Sapwn]

Thank you Ruthie, thank you dagmar!


I guess that soap calculators refer to the purest quality and that less pure lyes would give you higher superfat rate at the end.

 

[DeeAnna]

Basically, yes, you're right.

100% NaOH really doesn't exist in the real world. The 99% or higher NaOH will be expensive. I would not expect it to be normally available for purchase by regular consumers due to the cost -- it is a laboratory-grade product.

The 95-97% minimum NaOH product is considerably less expensive and is fine for soap. The impurities are salt (sodium chloride), sodium carbonates, water, and a tiny bit of metallic impurities. "Food grade" NaOH has a lower level of metallic impurities, but otherwise is pretty much the same as the "technical grade".

The stated percentage is the minimum NaOH in the product -- it can and is usually a bit higher. Having worked in the chemical industry for some years, the actual percentage will generally only be a ~little~ bit higher -- maybe a percent or so. There is no economic reason for the manufacturer to provide an extra-pure product, especially with a chemical as reactive as NaOH.

The "100% lye" sold in the USA for cleaning drains is NaOH, but the chemical analysis is not normally on the label. If that is the type of lye you are finding that costs less, you will probably be fine.

 

[Sapwn]

Thank you DeeAnna.

Now everything is clear.

 

[DeeAnna]

As a related comment, I do my soap recipe calculations with my own spreadsheet. I include the actual % of NaOH (or KOH) in the lye calculation, so the superfat % I choose for my soap recipe is closer to the actual superfat in the soap I make. If you don't adjust for NaOH purity, the actual superfat in the soap will be the % you choose plus the % of impurities in your NaOH product, all other things being equal. This "hidden" superfat isn't all bad -- it certainly is insurance against making a lye-heavy soap.

But I've wondered about the soaps talked about on this forum that get DOS quickly or that are so soft the soap cannot be unmolded -- especially when the soap maker uses higher percentages of polyunsaturated fats in the recipe. Does this hidden superfat contribute to these problems? Even if it doesn't, I'm just particular about things like this.