I born in Russia and lived there for 18 years, and from what I know kvass is non-alcoholic beverage. More like soda, just not so carbonated and sweet. It is hundreds of years old, made from bread but this days its made out of extract on large scale and authenticity suffers as well as taste. I remember home made kvass, when I was a kid and my mother always make some. I have not found one commercial example that would be even close to that.
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