Bread kvass

Bread kvass is the historically dominant kvass tradition — fermented stale rye bread, light, lightly alcoholic (0.5-1.5% ABV typical, sometimes higher), with a flavor that occupies the territory between root beer, dark malted milk, and a very mild beer. It is a peasant drink in origin (a way to use stale bread that would otherwise be wasted) and has remained continuously popular in Russia, Ukraine, Belarus, and the Baltic states, sold from refillable tank trucks on city streets in summer.

The substrate is dried, toasted rye bread — sometimes specifically toasted to dark brown for a deeper, more roasty flavor. The bread is soaked in hot water to extract sugars and starches, sweetened slightly (sugar, malt extract, or honey), and inoculated with either commercial yeast (modern fast version) or a kvass zakvaska (sourdough-like culture, traditional version). The fermentation produces lactic acid alongside ethanol, giving bread kvass a tangy edge that beer doesn't have.

Commercial Russian bread kvass is a major industrial product (Kvas Ochakovsky, Nikola, and others) and is generally pasteurized and carbonated; the homemade version is unpasteurized and lightly carbonated by primary fermentation alone. Both have a legitimate claim to the tradition. The homemade version is usually denser and more aromatic; the commercial version is more shelf-stable and consistent.