A dry and thin crust results in a crispy crust, a dry and thick crust results in a hard crust while a wet crust results in a chewy crust. If our goal is to obtain the driest and thinnest crust possible, we need strong gluten development to spread the dough thinly across the surface, and a short baking time.
1. Well developed gluten structure
A fully developed gluten structure contributes to a thinner crust. During mixing, glutenin and gliadin proteins are being aligned to form gluten strands. These gluten strands are impermeable which allows it to trap carbon dioxide gasses during fermentation. Carbon dioxide gasses are continuously released into the dough increasing its internal pressure, and causes the dough to expand and rise.
The more we mix, the more developed the gluten strands become, which creates many more spaces in the dough that can trap carbon dioxide gasses, causing the crumb of the loaf to be light with many layers or holes in them.
The light and airy nature of the dough results in a thin layer of crust that is separated from the rest of the crumb by many layers of air.
If the dough is not well developed, carbon dioxide gasses easily escapes out of the dough, leaving fewer layers of air in the dough, resulting in a denser bread. The dense and thick dough at the surface turns to a dense and thick crust when baked.
To develop a dough to full gluten development, mix the dough until it is slightly shiny and moist, the dough should stick together remaining as one lump of dough as the mixing arm kneads the dough.
When the dough is over mixed it will start to break down and that is evident with a very shiny, moist and sticky dough that does not lump together in the mixing bowl when mixed, but rather the dough is spread out evenly throughout the bowl and will eventually into a gooey mess.
2. Short baking time
The longer the dough is baked in the oven, the more moisture is removed from the surface of the dough, and the crust is formed deeper into the dough’s surface resulting in a thick crust; a dry and thick crust is hard, while a dry and thin crust is crispy.
Typically sourdough bread is baked until its internal temperature reaches 88 Celcius at the centre of the bread, there are a two methods that we can use to reduce the time it takes sourdough bread to reach this internal temperature of 88 Celcius.
- Lower hydration dough reduces baking time – when there is less water in the dough, there is less mass that needs to be heated up, hence it takes a shorter time for the dough to be fully baked. As the water content in the dough increases, there is more mass to be heated which takes a longer time, causing the surface of the dough to dry out over a longer period, resulting in a thicker crust.
- Long and thinly shaped dough reduces baking time – A long and thinly shaped dough has more surface area than a round dough of the same weight. The greater exposed surface area of a long and thin dough absorbs heat more quickly from the oven which causes its internal temperature to rise to 88 Celcius in a shorter time, resulting in a thinner crust.
As baking time decreases from using dough of a lower hydration and shaping our dough into a long and thin shaped, we reduce the time moisture is lost at the surface of the dough, to give us a thin and crispy crust.
It is important for all bread to be baked until its internal temperature reaches 88 Celcius, to achieve a crumb that is sufficiently cooked to prevent gumminess; bread baked to 88 Celcius will not be gummy but will be moist and tasty.
3. Appropriate steaming
Steaming is often introduce to sourdough bread to control the timing at which the crust is formed. Steaming creates a wet environment in the oven, which lowers the surface temperature of the dough and delays the formation of the crust.
If no steam is used, the crust sets rapidly and continues to harden over a longer period as the surface temperature of the dough is higher, resulting in a thick, dry and hard crust.
If too much steam is used, the surface of the dough remains at a lower temperature in a very moist environment, which makes it difficult for the crust to set, resulting in a thin but wet and chewy crust.
We typically steam until the crust takes on a rich brown coloration, then the oven is vent to release all the steam and the loaf finishes its bake in a dry environment. The initial steaming delays the formation of the crust to ensures that the crust is thin, and as the bake finishes without steam, the crust is allowed to dry out and become crispy.