A poster on a discussion board I frequent posted a note about a loaf that looked fine until it started to bake, then sagged in the middle of the loaf during baking. The poster was using a bread machine that would bake 2, 2.5 or 3 pound loaves and the effort under discussion was a 3-pound loaf. The question was not only what happened but if it might be related to the size of the loaf — was a 3 pound loaf actually too big for the machine.
I’m not an expert on bread machine baking, so I am operating at a disadvantage here. Other responses were to cut the yeast, cut the water, etc. All over the lot; not surprising, since this seemed like such a strange problem. Actually, it wasn’t a strange thing at all, just a bit of a twist on the flying crust, tunnel crust, problem.
Here’s what appeared to happen.
First, the bread machine is a closed environment, so the dough crust doesn’t dry out during final rise. This means that if the dough expands and then the crumb falls back, the crust can follow, instead of being stuck up in the air high and dry, as in a flying crust.
Second, the bread machine warms up as the dough is sitting in it, while an oven is already heated when the dough in put into the oven. This means that the bread machine dough doesn’t get a blast of hot air first during baking. The dough continues to rise normally until the bread machine reaches a critical temperature, then goes into high activity as it gets heated, then dies. The continuation of the normal activity leads to a bit of over rising, much like a loaf of dough that has been left on the counter a bit too long.
Third, I wasn’t sure what the hydration of the dough was, but in general, the potential for a flying crust seems to go up as the hydration goes up. I don’t think the bread here was particularly wet, so there isn’t anything to change in the hydration.
The combination of the first two things appears to have caused the collapse in the center of the loaf during baking. What happened was a flying crust that didn’t fly, that crashed back into the crumb.
My recommendation was to cut the yeast a bit and, if possible, cut the final rise time a bit. The goal is to reduce the amount of final rise enough to make the dough capable of expanding without then falling back.