Kvas with Raisin

Preheat the oven to 180°C (350°F). Arrange the sliced rye bread on a baking sheet and toast for 15 minutes, then flip and toast another 15 minutes until dark and almost burnt—this gives color and depth to the kvas.

Place the toasted bread and golden raisins in a large pot or heatproof container. Pour 4 L (4.2 qt) of boiled, warm water at about 90°C (194°F) over the bread. Stir to combine, cover loosely, and let it steep for 4–6 hours or until the liquid turns deep amber and smells pleasant.

Strain the liquid through a fine-mesh sieve or cheesecloth into another large container, pressing on the bread gently. Discard the solids (or save for bread kvass cake!). Add the 200 g (1 cup) sugar to the warm liquid and stir to dissolve fully. Let cool to about 30°C (86°F) — lukewarm, not hot.

When the liquid is lukewarm, sprinkle the dry yeast on top and stir well. Cover with a clean cloth and let sit in a warm place (20–24°C / 68–75°F) for 12 hours. you'll see bubbles and a slightly tangy aroma.

After 12 hours, pour the liquid into clean glass jars or bottles, but do not seal tightly — leave caps loose or use a cloth cover. Let ferments 12–24 hours at room temperature. Taste after 12 hours; when it becomes pleasantly tangy and fizzy, it's ready.

Taste the kvas — adjust sweetness with additional sugar (20 g / 1 Tbsp) if desired, then seal the bottles tightly. Refrigerate for at least 1 day to carbonate. Enjoy cold; store refrigerated for up to 2 weeks.