Steam and oven spring
Early in the bake, gas in the dough expands and the loaf springs upward. If the surface dries and hardens too soon, the crust acts like a lid. Steam keeps the surface moist and stretchy, so the loaf can finish expanding.
Lid on, then lid off
A preheated Dutch oven traps the steam that rises from the dough itself. Bake covered while the loaf springs, then take the lid off so the crust dries, browns and crisps. No pot? A pan of hot water on a lower rack makes steam too.
Test yourself
Questions from the interactive lesson, with the answer and the why.
What does early steam do for the loaf?
Delays the crust setting so the loaf keeps expanding. A moist surface stays stretchy and lets the loaf rise further.
True or false: Steam should stay in the oven for the whole bake so the crust turns crisp.
False. A wet crust stays soft and pale, so steam is removed later to let the surface dry and brown.
Fill the blank: Browning on the crust needs a ___ surface, which is why the lid comes off later.
Browning on the crust needs a dry surface, which is why the lid comes off later. Once the surface dries, it heats well past boiling and browns.
What went wrong? You bake a loaf covered the whole time. It rose well, but the crust is pale and soft.
The lid stayed on, so the surface never dried and browned. After the early steam, dry heat is needed to brown and crisp the crust.
A loaf baked without steam looks dense and its crust set early. What should you change next time?
Add steam for the first part of the bake. Steam keeps the surface stretchy so the loaf can expand.