Several factors can cause your bread to collapse, including adding too much water to your dough, there could be problems with the yeast you used, you may have over-proofed your bread dough, or maybe you did not knead dough enough.
Too much yeast—While it seems counterintuitive, too much yeast can actually cause your bread to collapse. The yeast will make the bread rise like crazy, but later it all falls in on itself. Try decreasing yeast by ¼ to ½ teaspoon.
It's Too Cold
That's because doughs proof best in warmer temps—around 80ºF is just right for yeast. If your kitchen is too cold, the yeast just doesn't have the right atmosphere to help the dough rise.
If it holds its shape, then it's ready for the next step. After the second rise, however, a baker is looking for the dough to spring back at her slowly when she pokes it. The second proving has given the bread more elasticity, and made it harder to deflate the air.
Put the dough in the fridge straight after shaping, covered with oiled cling film. It will start to rise but slow down as the dough chills. In the morning, allow it to come back to room temperature and finish rising 45 minutes to one hour before baking as usual.
What bakers call the “poke test” is the best way to tell if dough is ready to bake after its second rise. Lightly flour your finger and poke the dough down about 1". If the indent stays, it's ready to bake.
Similar to the signs of over proofed dough, an over proofed loaf will be very flat, without much rise or retention of shaping. Over proofing destroys the structural integrity of the bread, so loaves that have gone over are unable to hold their shape in the oven.
Deflate and reshape your over-proofed dough
First, deflate the dough. It actually feels kind of satisfying to press all that air out; you know, like you're breaking the rules and getting away with it. Next, reshape the dough into a loaf. Place it in its pan.
Because the dough is fermenting during both rises, if the process goes on for too long, the finished loaf of bread can have a sour, unpleasant taste. The finished loaf usually also has a dense texture and isn't sufficiently chewy. Over-proofed loaves of bread have a gummy or crumbly texture.
Once dough has risen to double its size, it must be pressed down or turned to prevent it from overproofing. If bread is allowed to rise to more than double its size, the gluten will stretch to the point of collapse and will no longer be able to hold the gas bubbles that provide necessary structure for the loaf.
Keep the dough closed for the duration of the proofing time according to your recipe. For example: 1-½ to 2 hours or until the dough has doubled in size for the first rise and 30 minutes for the second rise. Some recipes require two or even three proofs before baking.
If the dough doesn't spring back at all, you've likely over-proofed the dough. When the dough rises too much before it gets baked, it will collapse, rather than rise, in the oven's heat, and the crumb will be uneven and ragged.
“The first thing that springs to mind,” Bertinet says, “is that your dough is probably too cold.” Or, put another way, the water you're using isn't warm enough. “It's vital you give the yeast a helping hand, otherwise it'll just slumber lazily,” he says, adding that your water/ flour/salt/yeast ratio is also crucial.
Some ovens run hotter than its settings, some cooler. If the oven is too hot the loaf will be brown and crispy on the outside but doughy in the middle and may collapse as it cools. When bread is baked at too low a temperature it will not rise enough in the oven resulting in a dense and sunken loaf.
Bread collapses after baking due to moisture remaining in the crumb. As bread cools, moisture escapes causing the bread to shrink. As it is released from the crumb, water latches onto the crust, making it heavier. The crust is pulled down by gravity, and if the crumb structure isn't strong, the crumb contracts.
Don't overmix the batter. Try mixing quick breads together by hand or by machine on the lowest setting just until ingredients are incorporated. Then stir in nuts, dried fruits or other add-ins. Bake quick breads as soon as the ingredients are assembled and place the loaf pans in the center of the oven for best results.
Overproofing your dough will result in a flatting or collapsing of the dough. The reason for this is that the yeast in your bread has exhausted itself and does not have any more energy after you put it in the oven.
The dough should generally be proofed for around 1 to 4 hours at a warm temperature or overnight (or more) at a cold refrigerator temperature. As the proofing temperature increases, the total fermentation time will decrease.
Under Kneading
It is a tell-tale sign of not enough kneading if your bread dough cannot hold its shape or acts listless and fails to inflate. Instead of rising, the dough will spread out flat. The dough may even fall back onto itself and collapse as the gases produced by the yeast escapes.
Feel: Bread dough that has successfully risen/proofed will spring back slowly when poked and leave an indent. If it snaps back too quickly, it needs more time.
Lightly flour your index finger and press it gently into the dough, about to the bed of your fingernail. If the indentation remains and doesn't spring back/fill in, then the bread is well risen and ready for the oven. Have no fear, the "belly button" will rise and bake out just fine in the oven.