Put the slices of rye-bread in the oven (200 degrees Celsius) for about 45 mins, until they're dried. Boil the 8 liters of water. Crumble the dried rye-bread, put it in the boiling water for about 5 mins. Let it the water, and rye-bread rest for 4 hours, covered with a tea-cloth. Crumble the yeast, 15 mins before the 4 hours are over. Mix the crumbled yeast with some sugar and the luke warm water. Let it rest for 15 mins. Filter the water-rye-bread mix in a kitchen sieve. Carefully extract all water from the rye-bread. Wash, and peel the lemon. Add the lemon-peel, the sugar, the yeast and the peppermint. Stir the solution, and let it rest (covered) for 8 hours. Sieve the solution (tea-cloth). Bottle it. Put some raisins, a bit of lemon-peel, and a fresh leaf of peppermint in every bottle, close the bottles, and keep them in a cool place. Ready when the raisins start floating. Sieve the stuff one more time in a tea-cloth. Put the Kvasin the fridge 4 hours before drinking.
Serve in a Favorite Glass