Been making kefir from milk grains for eight years - successfully. Have often had some left over, especially in our summer when it ferments very quickly. An acquaintance said she had read about using overfermented kefir as a starter for sour dough.
I mixed a dough using about 300gm of plain flour, pinch of salt and kefir whey with a few curds, and left the bowl to stand in a zip-lock plastic bag in the pantry. After 24 hrs it had definitely risen, so I dropped a lump in my air fryer, and cooked it. It was "interesting" to say the least. An almost sour-dough ish taste. Would like to think it was healthy. Thoughts please.
Alison