Pineapple tepache is by far my most reliable fruit kvass, it has never failed. I use straight tap water, not filtered and don't need the pineapple to be organic.

Strawberry is slightly fussier but so far has worked. Don't boil the tops, no. Use more sugar than seems reasonable, and organic strawberries work better. Yes it's a wild fermentation but surely would be delicious started with some ginger bug too. I'll note that I live in a warm climate and house is cooled to 78F, that's about 26 in civilized degrees, maybe warmer than some houses. And I make sourdough all the time, other fermented pickles (not sauerkraut yet, live sauerkraut is available commercially here) not sure if that makes it easier.