Sergiev Posad in summer (posad meaning a trade settlement around a fortress) is a Russian culinary center offering traditional drinks on street sale. Tourist may wonder about yellow tanks featurung КВАС on their sides, selling cheap frothy dark drink by plastic glasses or already in bottles. If you miss such street vendors along the way, buy it by/in the Lavra. Monastyrsky kvas is considered the best brand. For traditional but flavored kvas tasting sourer visit the Skete with its kvas-making facility.
The top Russian cold drink is refreshing and nutritional kvas (quass) now back again more popular than any cola. It's a natural fermented drink (classically with bubbles) of black or regular rye bread, enjoyed in hot weather even by youth. Raw bread color defines kvas drink. Its alcohol content is very low - 0.05-1%. Kvas may be flavored with fruits or herbs like strawberries or mint. It's also used as a basis for a cold summer soup, okroshka.
Kvas was 1st mentioned in Rus chronicles in 989. In Russia, under Peter the Great, it was the top non-alcoholic drink in all society. In the 19th century it was reported to be consumed in excess by peasants, commoners and monks; in summer they drank it more than water. It's both a commercial product and homemade. Kvas was once sold during summer only, but is now produced, packaged and sold year-round in stores.
Kvas is made by natural fermentation of bread (wheat, rye, barley) and sometimes flavored with fruit, berries, raisins, or birch sap collected in early spring. Modern homemade kvas usually uses black or regular rye bread (often dried), baked into croutons, or fried (+ sugar or fruit like apples/raisins), and with a yeast culture and ferment.
Commercial kvas (especially cheaper varieties) is made like many other soft drinks, using sugar, carbonated water, malt extract, and flavourings. Better brands (often made by beer rather than soft drink producers) usually use some traditional technology to brew their products. Kvas is commonly served unfiltered, with yeast still in it, which adds to its unique flavor and its high vitamin B content.