Why my rye keeps collapsing (and what finally fixed it)
For most of the summer every 70% rye I proofed in the kitchen came out of the oven with a dent in the middle. I blamed the starter, then the flour, then the weather. The real culprit was simpler: I was proofing by the clock and not by the dough. With the kitchen at 27 °C, ninety minutes was already too long. Cutting the final proof to fifty minutes and baking the moment the surface showed the first cracks gave me a loaf with an even crumb and no cave.
Two other small things helped: a heavier dusting of rye on the banneton, and letting the loaf rest a full day before slicing. Rye needs the time.