This is a tangent from a thread that I started when looking into how to corn my own beef:
Recipes calling for potassium nitrate (saltpeter) and/or sodium nitrite present a geuine retail challenge. I wonder if this stuff isn't used in meth labs or the like, to justify how hard it is to get, and how frankly suspicious some people seem that you're asking for it at all.
Supermarkets won't have it. I found a local meat-curing butcher who uses it but refuses to sell it retail, because he says things can go way wrong if it's misused. Apparently, saltpeter is part of smoke bombs, fireworks, certain fertilizers, black powder gunpowder, etc. I saw online recommendations that you can sometimes get it at compounding pharmacies. Another said that garden stores sometimes stock it. When I called a garden store and asked if they stocked potassium nitrate, lo and behold, they do, in the form a product used for killing tree stumps! (You drill a whole in the stump, dissolve potassium nitrate in the whole, and weeks later the stump is falling apart dead.) The garden store said they obviously couldn't take responsibility for uses in food preparation.
Turns out I actually had this product in my garage, after all that wasted driving around! Checked a govt. website, and indeed it is 100% potassium nitrate:
So I'm going for it. If you hear nothing from me in a few weeks time, then think twice about using stump remover in your cuisine.
Also, while I can only speak from internet browsing, I'm gathering that what happens to potassium nitrate during the brining is that it combines with meat proteins and the like and converts into sodium nitrite. The conversion process, says one writer, lengthens the time as compared to just starting with sodium nitrite, but the added time makes for better flavor.