Slice the Borodinsky bread, place the slices on a baking sheet and lightly dry them in the oven.
Line the bottom of the jar with raisins.
Place dried Borodino bread on top of the raisins.
Add sugar and dry yeast to the jar.
Pour boiled water over the ingredients.
Mix the ingredients thoroughly, cover the jar with cling film and leave in a warm place for 2 hours.
Remove the cling film and strain the kvass through a fine sieve.
Pour homemade kvass on Borodinsky bread into cups. Enjoy!