This is my favorite probiotic, a Slavic/Baltic beverage made from fermented rye bread. You got to be a little brave to drink this at the start. Has a taste that feels like it will put hairs on your chest thus it takes a little getting use to but well worth the health benefits.
Mainly due to kombucha becoming mainstream and a little "Hollywood" its my natural inclination to go for an alternative and root for the underdog.
Give it a try and see what you think. Kvas with blueberry is my favorite.