We weren't surprised when the kvass we brewed based on East End's recipe went sour, with the minimal hopping, low gravity starchy wort, and bread yeast it was something we suspected might happen. Luckily a low gravity, lightly hopped beer makes for a good base for sour flavors (as we tasted at East End in a sample of unintentionally sour Kvass).
East End Kvass Clone
Appearance – Surprisingly clear (but still slightly hazy) pale orange. The thin white head floating on top has poor retention. The beer has gotten much clearer over the last few weeks as the yeast and the starches from the bread have slowly settled to the bottoms of the bottles.
Smell – Caraway is the first thing I get, as well as a yeasty/bready malt character. There is a sour, yogurtish component to the aroma as well.
Taste – Tangy lactic acidity followed by warm bread crust maltiness. The caraway comes in the finish, but it isn't as strong as in the aroma. The acidity isn't especially strong, just enough to make for a bright, interesting beer.
Mouthfeel – Medium body, with moderate carbonation. The body is thicker than you'd expect for such a low gravity beer.
Drinkability & Notes – A refreshing beer that is easier to drink than the highly acidic Berliner Weisses that I tend to make. I'd be interested to see if this method (minimal hopping and fermenting with bread yeast, could work for other sorts of low gravity sours).