1911 Encyclopædia Britannica/Kvass

KVASS, or Kwass (a Russian word for “leaven”), one of the national alcoholic drinks of Russia, and popular also in eastern Europe. It is made, by a simultaneous acid and alcoholic fermentation, of wheat, rye, barley and buckwheat meal or of rye-bread, with the addition of sugar or fruit. It has been a universal drink in Russia since the 16th century. Though in the large towns it is made commercially, elsewhere it is frequently an article of domestic production. Kvass is of very low alcoholic content (0.7 to 2.2%). There are, beside the ordinary kind, superior forms of the drink, such as apple or raspberry kvass.