What happens to doughnuts that have fermented too long in the proofing stage?

When doughnuts have fermented for too long in the proofing stage, they are prone to browning too quickly in the fryer. This occurs because an over-proofed dough has larger gas bubbles and a weakened gluten structure, which can cause the surface of the doughnut to heat up faster than the interior. When the doughnut is placed in hot oil, the outer layer may cook and brown rapidly while the inside might not have enough structure to support itself, leading to an undesirable texture and uneven cooking.

Additionally, the excessive fermentation can result in a doughnut that may taste off due to the buildup of acids, and it can indeed affect the overall quality of the product. While longer fermentation times can develop flavors, there is a delicate balance, and going beyond that can result in an undesirable outcome, making the rapid browning an important factor. The notion that an over-fermented doughnut takes longer to fry or becomes denser is not accurate, as these aspects are typically associated with different issues in dough preparation or frying techniques.