I’m taking my first crack at making Beet Kvass and have just a little bit of experience with fermenting. I made three jars like this with slight variations (w/lemon, without lemon; variations on the salt) and this one looks like the seal was letting in some air. They have been fermenting for about a week. The other two jars had some scum but overall seem to be a success. This one makes me pause a bit... the mold does not look good and I’m wondering if the location was a little bit too warm in addition to the questionable seal. However, the beets and liquid below still have their lovely pink color, so I’m hoping you can help. Important to note that there are mint leaves floating at the top, which may distort the color a bit. Thoughts?
I am glad to hear your other two turned out well. I can’t imagine your variations have anything to do with the mold, more likely the seal, as you suspect. Also the mint floating on top could have given the mold a place to land, but not caused it.
A few things that you can do to prevent that in the future is to fill the water line a little higher in the jar. Less airspace means that there is less oxygen for the CO2 to push out (whether you are burping the jar or using these one way lids).
As far as this kvass goes. It looks like a pretty big bloom of mold and the ferment hasn’t been going very long so I can’t say with confidence that is as acidic as it should be. My guess is that if you carefully remove it, make sure that you got it and a little of the kvass underneath, and make sure the jar sides are clean, that it may still taste off or moldy. But that is what you would do in order to tell, if what looks good is good or not. In this case my instinct would be to compost it and start over.
I hope that helps,