I found both dark and light rye bread at the store but it was the factory-made kind. I definitely made mistakes with both batches including adding way too much bread to the light kvass.the bottles need a day to carbonate then we shall see how well they turned out. Not that I have any reference for the flavor.
The raisins are there as a source of yeast and really doesn't impact the flavor that much as this amount. They can be removed if you use another source of yeast.