How long does an opened bottle of commercially made kvass last in the fridge?
I would have expected the answer to be "weeks", given that it's fermented and would likely just slowly get stronger, but a bottle of Belorussian kvass 1 I recently acquired says it has to be kept below 6°C and "не более суток" (not longer than a day).
Best Answer
In this case, I recommend you follow the manufacturer’s label text.
Traditional kvass is fermented (often in a home setting), and will contain live microorganisms, that keep unwanted ones at bay, similar to a well-established sourdough culture.
But of course there are a few caveats:
In short, while your home-fermented drink will keep for a while, the safe approach is to stick to the instructions.