|Kvass (or kvas) is a very low alcohol content drink made from black or rye bread. It is particularly popular in Eastern and Central Europe. According to Wikipedia, "Its origins go back 5,000 years to the beginnings of beer production."
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"Kvass has been a common drink in Eastern Europe since ancient times. It was first mentioned in Old Russian Chronicles in the year 989. In Russia, under Peter the Great, it was the most common non-alcoholic drink in every class of society. Later, in the 19th century, it was reported to be consumed in excess by peasants, low-class citizens, and monks; it was, it is sometimes said, usual for them to drink more kvass than water. It has been both a commercial product and homemade. It used to be consumed widely in most Slavic countries, where in almost every city there are kvass vendors on the street. And "despite its humble folk origins, the fermented-bread drink brewed by Russians for over 1000 years has become a booming multimillion-dollar industry." Moreover, "once sold only during the summer out of wheeled yellow tanks the size of beer barrels, kvas is now bottled, canned and shipped across the country all year round."