Fascinating! I am something of an amateur baker and I'd never heard of it. I assume it comes from periods of high wheat prices, since it also heavily uses rye

Fascinating! I am something of an amateur baker and I'd never heard of it. I assume it comes from periods of high wheat prices, since it also heavily uses rye? Sadly rye (which I have something of a personal taste for, mostly in whiskey though!) is also being impacted by the economy's preference for corn; global production numbers for rye have been falling steadily particularly in the former Soviet countries. I have had difficulty sourcing rye flour that's not eye-wateringly expensive. You are perhaps already familiar, but in Mesoamerica where corn originated, it is generally processed into flour only after alkaline processing. The resulting flour, typically sold as "masa" in the US, is distinct from simple ground corn (cornmeal or corn flour in the US). The difference is quite striking, both culinarily and nutritionally. It still doesn't form the gluten that wheat dough, does, so I haven't had good luck making European-style breads with it (though I'd love to, because I live with someone who has a wheat allergy).