Kvass is a lightly fermented beverage made from stale bread — a tradition common across Russia, Ukraine, and the Baltic states that represents the most economical possible application of fermentation: using what would otherwise be waste (old rye bread) to produce a nourishing, mildly alcoholic drink through wild fermentation. Katz documented kvass as an entry point into fermentation for beginners — requiring no equipment beyond a container and demonstrating the fundamental principle of fermentation in days rather than weeks.
A lightly fermented beverage (approximately 1% alcohol) made from dried or toasted rye bread, water, and sugar, fermented at room temperature for 1–3 days through wild yeast and bacterial activity. The toast on the bread provides Maillard compounds that give kvass its characteristic dark colour and complex flavour.
- The bread must be toasted to near-burning before steeping — pale bread produces pale, flat kvass without the roasted depth that defines the traditional version - The steep produces a "bread tea" — the flavour compounds from the toast dissolve in hot water, producing the base that fermentation then transforms - Wild yeast present on the bread and in the environment inoculates the steep naturally — no starter required for traditional kvass - Fermentation is complete in 1–3 days when the liquid tastes pleasantly sour and slightly fizzy. Over-fermentation produces an aggressively sour, alcoholic result unsuited to drinking [VERIFY timing] - Strain and refrigerate when done — cold temperature halts active fermentation and preserves the desired flavour stage
THE ART OF FERMENTATION + OTTOLENGHI JERUSALEM SECOND BATCH