I see this instruction when making rye bread: let it proof until soft. How can I tell when it's soft? I keep baking Jewish rye and letting it proof longer and longer and it certainly starts to feel pillowy and smooth (not sticky) but I don't know how long that should go on for. I ask because my bread is splitting down the sides which suggests to me that it's under-proofed. It tastes good and isn't gummy but the loaf is flat(ish) and splits.
I wonder if it's worth mentioning that I'm proofing this loaf in a parchment paper 'couche' supported by kitchen towels. I pick up the paper and set it on a baking sheet that goes into the oven. The paper is typically at least a little stuck to the sides of the loaf when it goes in.