Квас/Kvas

It's a Ukrainian/Russian beverage sold on the streets out of large tanks in the summer. I quite like it. You can also buy it in stores in bottles.

From Wikipedia:

Kvass, kvas, or quass (from Old East Slavic квасъ, kvasŭ, meaning "yeast" or "leaven";^[1] today, in Belarusian: квас, kvas, сиривець, siriviets; Lithuanian: gira; Russian: квас, kvas; in Ukrainian: квас, хлібний квас or сирівець, kvas, khlibnyy kvas or syrivets; Polish kwas chlebowy) is a fermented bread. The colour of the bread used contributes to the colour of the resulting drink. It is classified as a non-alcoholic drink by Russian standards, as the alcohol^[2] Overall, the alcohol content is low (0.05% - 1.0%).^[3] It is often flavoured with fruits or herbs such as strawberries or mint. Kvass is also used for preparing a cold summertime soup called okroshka.^[4] beverage made from black or regular rye content from fermentation is typically less than 1.2%.

It is popular in Russia, Belarus, Ukraine, Lithuania, Latvia, and other Eastern and Central European, where one can see many kvass vendors in the streets.^[5] Kvass is also popular in Harbin^[6] and Xinjiang, areas within China that are influenced by Russian culture. countries as well as in former Soviet states, such as Kazakhstan, Uzbekistan.

Kvass is made by the natural fermentation of bread, such as wheat, rye, or barley, and sometimes flavoured using fruit, berries, raisins, or birch sap collected in the early spring. Modern homemade kvass most often uses black or regular rye bread, usually dried, baked into croutons (called suhari), or fried, with the addition of sugar or fruit (e.g. apples or raisins), and with a yeast culture and zakvaska ("kvass fermentation starter").
Commercial kvass, especially less expensive varieties, is occasionally made like many other soft drinks, using sugar, carbonated water, malt extract, and flavourings. Better brands, often made by beer rather than soft drink manufacturers, usually use a variation of the traditional process to brew their products. Kvass is commonly served unfiltered, with the yeast still in it, which adds to its unique flavour as well as its high vitamin B content.
There is only one brewery in the United States that brews a Kvass year round. That is the Beaver Brewing Company in Beaver Falls Pennsylvania. They make it with the addition of raisins and lemons.