Kvass is a traditional Balto-Slavic sour drink, which is prepared on the basis of fermentation from flour and malt (rye, barley) or from dry rye bread, sometimes with the addition of odorous herbs, honey, honeycombs; also prepared from beets, fruits, berries. Kvass is used not only as a drink, but is also the basis for the classic cold soup of Russian cuisine (okroshka, botvinia, etc.).