Cut the rye bread into 1/4-inch slices (it should contain only rye flour, and no additives or preservatives.)

Spread the bread on cookie sheets and bake for about 30 minutes at 325 degrees F. When cool, chop into 1/4-inch pieces in a food processor.

Bring 4 quarts of water to a boil and then cool to 175 degrees F. Add the bread, stir well, cover with a lid and leave in a warm place (76-78 degrees F) for 1 hour. Strain and reserve both the bread and the liquid.

Bring another 2 1/2 quarts of water to a boil, cool down to 175 degrees F and add the reserved bread. Cover with a lid and leave in a warm place for 1 1/2 hours. Strain and discard the bread. Combine both batches of liquid.

Place 1/4 cup sugar and 1 tablespoon water in a small cast-iron skillet. Stir continuously over heat until the mixture turns golden brown. (Be careful not to burn it.) Remove from heat and gradually blend in 1/2 cup of the reserved liquid. Then stir this mixture into the entire batch of liquid.

In a small saucepan place 1 cup water and the remaining 1 1/4 cups sugar. Bring to a boil, lower the heat and simmer for 10 minutes, skimming once or twice. Stir this syrup into the reserved liquid and allow the mixture to come to room temperature (about 75 degrees F).

Mix the yeast with the flour and combine with 1 cup of the liquid. Return this yeast mixture to the pot. Make an X of masking tape across the top of the pot. Cover the pot with 2 layers of cheesecloth or a clean kitchen towel and leave in a warm place (73-78 degrees F) for 8-12 hours or overnight. Cool the kvass to about 50-54 degrees F. Transfer to bottles, seal tightly and refrigerate for 24 hours. The kvass will keep in the refrigerator for 2-3 days.