Underproofed
Very commonFermentation rate depends strongly on temperature, and a dough in a cool kitchen takes considerably longer than the same dough in a warm one. A recipe’s stated time describes the kitchen it was written in. Baked early, the dough has not accumulated enough gas, and the structure sets around a smaller volume.
The variable underneath
Dough temperature
How to tell after the fact: A loaf that over-proved in less time than the recipe stated, in a warm kitchen, indicates dough that started warm.
What to change
Judge proofing by the dough, not the clock
Press a floured fingertip about a centimetre into the dough. If the indentation springs back fully and quickly it needs longer. If it springs back slowly and partly, it is ready. If it does not spring back at all and the surface may sag, it has gone too far.
Any yeasted or naturally leavened dough at final proof. Less informative during bulk fermentation, where volume and surface condition are better guides.
Trade-off: Requires handling the dough, which slightly disturbs the surface. This is immaterial compared with baking at the wrong point.
Control the dough temperature via the water
Adjust the temperature of the mixing water to bring the finished dough to a consistent target. Warmer water in a cold kitchen, cooler water in a warm one. Measure the dough after mixing so the adjustment can be repeated.
Any fermented dough. Particularly valuable for sourdough, where timing is otherwise unpredictable.
Trade-off: Requires a thermometer to do properly, and a note of what worked last time.