The deep mahogany crust comes from dunking raw dough in a caustic lye bath — the same chemistry used in soap-making — before baking flips it harmless.
A soft wheat-and-malt dough is shaped into the telltale knot, briefly bathed in food-grade lye, scored, and baked until the surface blisters into a deep brown, faintly bitter shell around a chewy interior. Sold split and buttered from bakery windows and beer garden carts across Bavaria.