Milu's Fast Kvass

Steps

1. Preheat oven to 180°C (350°F). Cut the rye bread into cubes and bake for 40-45 minutes, turning every 5-10 minutes to ensure even toasting. The bread should be dark brown but not burnt.
2. Place the toasted bread cubes in a large bowl and pour 2.5 liters (10.5 cups) of boiling water over them. Let soak for 2 hours.
3. Add an additional 2 liters (8.5 cups) of boiling water to the mixture (add 1 more liter/4 cups if the bread absorbed a lot of water). Let sit for another 15-20 minutes.
4. In a small bowl, mix 0.5g (1/8 tsp) dry yeast with 1 teaspoon sugar and ⅜ cup (1/3 cup) lukewarm water. Mix well and let sit for 15 minutes until frothy.
5. Strain the bread mixture through a fine mesh sieve or cheesecloth into another large bowl, squeezing out as much liquid as possible. Add 4⅝ oz (2/3 cup) sugar and stir until dissolved.
6. Let the mixture cool to room temperature. Once cooled, add the yeast mixture and stir well.
7. Pour the kvass into clean glass jars or bottles, leaving 5 cm (2 inches) of space at the top. Cover with a cloth or loose lid to allow fermentation gases to escape.
8. Let the jars sit at room temperature for 24 hours to ferment. The longer it ferments, the more sour it will become.
9. Pour the kvass into clean plastic bottles, leaving any sediment behind. Add 2 teaspoons of sugar per bottle. Seal bottles tightly and leave at room temperature for 6-12 hours until the bottles feel firm to the touch.
10. Check bottles after 6 hours by gently squeezing. When firm, release some gas by briefly opening, then reseal and refrigerate.
11. Chill in refrigerator for 1 day before serving. If it still tastes yeasty, wait an additional 12-24 hours until the yeast flavor disappears and sediment forms at the bottom.