What is the name of this traditional Slavic and Baltic fermented beverage that is used for a flavor in Fruktime and commonly made from rye bread whose colour contributes to the resulting colour of the drink?
Fruktime:  It is made in various flavouring variants: Buratino (caramel), Tarhun (tarragon), Hand bell, Lemonade, Pear, Strawberry, Apple, Cream soda, Kvass, and Baikal (Natural). Kvass: Kvass is a traditional Slavic and Baltic fermented beverage commonly made from rye bread, known in many Eastern European countries and especially in Russia as black bread. Kvass:  The colour of the bread used contributes to the colour of the resulting drink.
Kvass