Turn over a bar of the Heritage Bar and read the label, and you will come to the words Sodium Hydroxide (Lye). It is natural to stop there and wonder whether there is lye in the soap.
It is a fair thing to wonder, and it deserves a plain answer. The short version is that lye is how soap is made, and when the job is done properly, the lye is no longer there as lye. The longer version is worth knowing, because it explains a good deal about what soap actually is.
What Lye Is
Lye is the common name for sodium hydroxide, a strong alkali. On its own it is not something you would want anywhere near your hands. In the workshop, Andrea handles it with gloves and eye protection, measures it by weight, and mixes it with liquid before it ever meets the fats. She treats it the way a cook treats a very hot pan: with respect, and with a plan.
That may sound like an odd thing to put in soap. But there is no such thing as real soap made without it. Bars sold as "lye-free" are usually either a detergent, which is a different product altogether, or a melt-and-pour base that someone else already made with lye before it was melted down and reshaped.
What Happens in the Pot
When lye solution is stirred into fats and oils, a chemical reaction begins. It is called saponification, from the Latin word for soap. The lye and the fats react with each other and are both used up in the process, and what forms in their place is soap, along with a natural byproduct called glycerin.
This is the part people find surprising. The lye does not sit inside the finished bar like an ingredient in a cake. It is transformed. The tallow, coconut oil, olive oil and the rest are no longer quite what they were either. Together they have become something new.
In cold process soap, which is how every Provision bar is made, most of this reaction takes place in the first day or two after the soap is poured into the mold. We let the soap set, cut it into bars, and move them to the cure shelf.
Why It Still Appears on the Label
If the lye is used up, you might wonder why we list it at all. We list it because it is what we put in. An ingredient list tells you what went into the batch, and sodium hydroxide went in. Leaving it off would make the label look gentler, but it would be less honest, and we would rather you know exactly how your soap was made.
You will see the same thing on other handmade soaps. Some makers write the ingredients in their saponified form, such as "sodium tallowate" or "saponified olive oil," which describes what the fats became after reacting with lye. Both ways of writing it point to the same process.
Getting the Recipe Right
The reason a properly made bar contains no free lye comes down to careful measuring. Every fat needs a particular amount of lye to turn fully into soap, and that amount is different for tallow than it is for olive oil or shea butter. Soap makers calculate the recipe so there is slightly less lye than the fats could use. That way all of the lye finds something to react with, and a small amount of fat is left over in the bar.
Andrea weighs every ingredient for every batch. Her culinary training shows up here more than anywhere else. A recipe that works is one that is followed exactly, and there is no eyeballing a measurement when the measurement matters this much.
Where the Cure Comes In
We wrote about the cure in Issue No. 3, so we will not go over all of it again. In short, after the bars are cut they rest for a full eight weeks. During that time water leaves the bar, the soap hardens, and the reaction finishes settling. A bar that has cured is a finished bar. We do not ship soap before that time is up.
A Note on Your Own Skin
Knowing how soap is made is one thing. Knowing how a particular soap will suit you is another, and we cannot tell you that. If you have any concerns, patch test first and ask your doctor. That is the same advice we give in our FAQ, and we mean it.
So, Is There Lye in My Soap?
Lye went into it, and it is the reason it is soap at all. By the time a properly made, fully cured bar reaches you, that lye has done its work and become part of something else. We put it on the label because we would rather explain it than hide it.
If you would like to read the full ingredient list for yourself, it is on the page for The Heritage Bar, along with how we make it and how to care for it.
Welcome back to The Provision Press, our journal of craft, intention, and the art of making things well.
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