Rye Bread Kvass

Preheat the oven to 375°F (190°C). Spread the rye bread pieces on a baking sheet and toast until deeply golden and crispy, about 10–15 minutes, stirring occasionally.

Place the toasted rye bread pieces in a large glass jar or heatproof container. Pour the boiling water over the bread, ensuring all pieces are submerged.

Cover the jar loosely and let the bread soak and cool to room temperature, about 2–3 hours. Strain the liquid through a fine sieve or cheesecloth into a clean container, pressing gently to extract all the flavor.

Pour the rye liquid into a clean jar. Dissolve the yeast in a small amount of warm water and stir it into the liquid along with the sugar, mixing well.

Cover the jar with a loose cloth or paper towel and let it ferment at room temperature for 12–24 hours, until the mixture develops a slightly tangy flavor and light carbonation.

Strain the kvass through cheesecloth into bottles, discarding any sediment. Refrigerate until chilled and serve cold in glasses.