While you *can* bake sourdough on a baking sheet or pan, a Dutch oven is highly recommended for achieving optimal crust and oven spring due to its ability to trap steam.
Baking sourdough in a Dutch oven creates a steamy environment that is crucial for a good rise and a crispy crust. Here's why:
Steam Retention: The tightly sealed lid of a Dutch oven traps the moisture released from the dough as it bakes. This steam prevents the crust from forming too quickly, allowing the bread to expand fully (oven spring) before the crust sets.
Even Heat Distribution: Dutch ovens, especially cast iron ones, provide excellent heat distribution. This ensures that the bread bakes evenly from all sides, preventing hot spots and promoting consistent browning.
Crust Development: The combination of steam and even heat results in a beautifully crisp and deeply colored crust. The trapped steam allows the starches on the surface of the dough to gelatinize properly, leading to that desirable chewy texture.
Baking on a baking sheet or pan will result in a flatter loaf with a less crispy crust because the steam escapes and the heat distribution is less even. You can try to create steam in your oven by placing a pan of hot water on the bottom rack, but it's not as effective as a Dutch oven.
If you don't have a Dutch oven, you can try using a pizza stone placed in the oven with a pan of hot water underneath to simulate a steamy environment. While not as effective as a Dutch oven, it can improve your crust compared to baking on a bare baking sheet.