A great sourdough crust is not accidental. It is the result of precise hydration, steam at the right moment, a Dutch oven, and a hot enough oven to cause the dramatic oven spring that produces those dramatic blisters and that distinctive crackle. We break down exactly what happens during each phase of the bake so you can troubleshoot your own loaves.
The sourdough crust forms in three distinct phases. In the first ten minutes -- what bakers call the oven spring phase -- the dough expands rapidly as water vaporizes and CO2 in the gas bubbles expands with the heat. This is when your scoring cuts open up and the ear of the loaf forms. To get maximum oven spring, you need two things: a very hot oven (at least 500 degrees Fahrenheit / 260 Celsius) and steam. The steam keeps the crust surface moist and extensible, allowing it to expand without tearing randomly. Baking inside a preheated Dutch oven traps the steam released by the dough itself, which is why Dutch oven loaves consistently outperform those baked on a stone. After the first 20 minutes, you remove the lid of the Dutch oven. Now the crust is set enough to hold its shape, and you want dry heat to drive off moisture and create the Maillard reaction -- the browning that produces those complex, slightly bitter-toasty flavors. A properly dark crust is not burnt. It is essential. Under-baked sourdough with a pale crust is soft and slightly gummy inside. Bake until the internal temperature reaches 205-210 degrees Fahrenheit, and let it cool fully before cutting -- the crumb continues to set as steam redistributes during the first hour off the heat.