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.
I mean I finished these. The two types of the resulted in surprisingly different flavors. The dark rye one wound up being sickly sweet so I think the sugar was too much.