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.
My Pullman loaves will sometimes do that on sides and bottom. I theorize that it is about the core shrinking and the edges being strong enough to resist but the flat sides and bottom are not. For a while I thought that reducing the hydration a bit helped but I'm not convinced. If I go too far with scald, Tangzhong, or potato flakes it is worse. The sinkage is small but I notice it.
One thing I was wondering is if the speed of cooling would affect it at all. I usually do two loaves at a time, so I was thinking to cool one in my garage (50f) and one on my oven set to proof (79)
Use less water. Enjoy!
You mean lower the hydration of my dough?
Yep. Enjoy!
I sometimes get some concavity, too - not usually as much. In your loaves - which are great-looking! - is the concave area cylindrical, with an axis parallel to the big slash, or circular, or what?
I suspect that this kind of curving action comes from a weakness or discontinuity in the crust. The crust tries to shrink as it cools and there is usually some kind of a seam or fold along the bottom. There may also be some circular structure introduced by the shaping. The loaf isn't usually symmetrical even if it looks like it from the outside. The cooling loaf tries to shrink so there is a pull in the crust from the inside, and the crust also tries to shrink from the outer circumference in.
Asymmetries and seams could end up as shape changes. I doubt that it's a change in the gas pressure.
You could try turning off the oven, maybe cracking the door, and letting the loaves cool down in the oven for a while. See if that makes a difference.
TomP
The concave is even, shaped like a bowel. It does not favor one direction (like which way the slash goes)
I was wondering if my thickish and well done crust contributes to this at all , vs a thinner lighter crust.
Not sure if you can see in this picture, but the bottom crust has cracked running all the way around the circumference. I also sometimes get crazing on the top during cooling (although not today)
I can see the cracking. It's not something I've noticed in my own loaves. I do sometimes get crazing on the top, too.
If you were to bake a loaf that is somewhat underproofed, the bottom will often be rounded, in a convex way. That might offset, or oppose, a tendency to go concave. Why don't you give that a try, along with a slow cooldown in the turned-off oven.
I can't get over your kitchen being 60°.
It seems from your description that the reason for the concavity of loaves after cooling could be due to a crust that is too strong, compressing the bottom part of the crumb. This could be related to the baking process at a high temperature or leaving the loaf covered for too long.
Room temp? Straight from the reefer? From a proofer? Somewhere in between?
Eg: I always bake right out of a 38°F reefer and never have the problem.
Just spitballin' here. Best wishes. Dave
Trimbandit, timely post, I was going to ask the same question about my loaves. I am baking with 100% home milled whole wheat, sourdough, and my hydration lately has been in the 87% range and am noticing the same concave at the bottom. Can't say for sure but it also seems to loose height as well as it cools. My bake is normally not under proofed - if any , final proof is a bit over proofed. I will start backing off on the hydration and see if that helps.
Here is a photo of the crumb of a recent bake - not as concave as some, but you can see a bit of compression towards the bottom. This one was not overprooofed