Those questions all came in over the weekend, and they’re good ones. I’m no chemist, but I’ll do my best to answer.
Lye is an alkaline substance, which in chemical terms means it’s on the opposite side of the pH scale relative to an acid, but that doesn’t mean it’s harmless. A strong alkaline, like lye, is every bit as capable of delivering a bad chemical burn as a strong acid. In the past lye was a common household chemical, used in some forms of food preparation but also to make soap. The pioneers in America employed lye for just that purpose.
But where did they get it? The answer is they made it. How? By soaking wood ashes in barrels and collecting the caustic liquid that leached out the bottom. The main chemical ingredient in this kind of homemade lye (correct me if I’m wrong, chemists) was/is calcium carbonate, the same compound that native peoples in Central America have historically used to treat corn to make tortillas. This is the stuff that can be found in many Mexican markets and is commonly referred to as “cal.”
That, however is just one type of lye. So-called “Chinese lye” is a mixture of potassium carbonate and sodium bicarbonate (baking soda), and is frequently used in cookery, notably to make rice dumplings and buns.
The lye that’s commonly used for European pretzels (and bagels) is sodium hydroxide, also called “caustic soda” which is produced industrially. Prior to its invention (isolation), it’s my understanding that Europeans primarily used sodium carbonate, which can be extracted from trees and plants, but is just as frequently mined from alkaline lake beds. This was the compound that peoples dating back to the Egyptians used to wash clothes and preserve food, known as “natron.”
What does all this have to do with pretzels? I confess I’m not sure. Only that somehow, somewhere, strong alkalines were introduced into the production of some kinds of northern European breads. Regarding which, I can’t say I’m sure that some of the non-European lyes I mentioned would work the same way for pretzel-making. Had I had the time and wherewithal, it would have made an interesting experiment. Oh well. Call it another item on Joe’s ever-lengthening “to-do” list.
UPDATE: Reader Bill adds:
Potassium hydroxide is the lye component derived from wood ashes (hardwood). Calcium carbonate (lime) is also present in an even larger proportion.
UPDATE: Reader Bronwyn says:
Might see if I can nab some NaOH and KOH from work and do that wee pretzel lye comparison for you. Can’t think there’d be a huge difference, as it’s the (OH-) that does the work. Compare with NaNO3 and KNO3 which seem to be able to be used interchangeably in curing meat.