bottom of loaves get concave when cooling
I have an issue where my loaves come out of the oven with a flat bottom, but then it sucks in to become concave when cooling. I'm not sure what is causing this. I bake at 480f for 30 covered and 25 with cover off. It cools on a wire rack in my kitchen which is ~60 degrees. Aside from the aesthetics, the crust pulling in compresses the bottom of the crumb a lbit. I am wondering if this has something to do with my fairly robust crust which is getting pulled inward on the bottom as the pressure inside the loaf decreases during cooling. The bottom of the loaf would be be more susceptible to this as it would have less strength than the domed curve of the upper loaf (or so I would imagine from my hs physics)
Hydration is 77-80% and I am using central milling bread flour.