I have a Russian wife and family over there. Although I personally LOVE the stuff most of my American friends don't care for it. I have never seen anyone add flower. We usually get old stale bread. They add bread yeast too. I don't add mint, but dried sour cherries are awesome!
My experience with kvas is that most of y American friends don't care for it. But I love the stuff! My wife is Russian and the recipe you have is pretty much a standard. That said, there are as many variations on kvas as beer, I would suppose.
Actually, home brewing is a Misdemeanor, class A (I believe) with a 1 year jail and $2000 fine.
This is EXACTLY why I refuse to brew anything alcoholic! I simply brew a yeast-based nutritional supplement. :fro: