The fresh crackling sound that sourdough makes is a sign that the crust is thin, dry and crispy.
Sourdough bread that has a dry, thin and crispy crust makes a crackling sound as it cools down after being taken out of the oven.
During baking, the steam that is introduced in the oven helps to moisten and allows the surface of the dough to remain stretchable as the dough expands during oven spring.
The surface of the dough is stretched without ripping during oven spring and the hard crust sets when the loaf’s volume is at its maximum.The formation of the hard crust is perfect with no cracks on it surface due to the moistening effect of steam.
The baked loaf is the largest in volume as the temperature of the loaf is the highest when it is first removed from the oven. As the baked loaf drops in temperature during cooling, the crust contracts, causing the dry and brittle crust (initially with no cracks) to crack, which causes a light crackling sound as the crust structure splits.
When the crust is dry and thin, it is weak and brittle which cracks much more easily and produces a crackling sound. Dry and thick crust is strong and hard and does not crack easily and hence does not produce a crackling sound. Wet crust that is either thin or thick is pliable and does not crack, and hence does not produce a crackling sound.
If your sourdough bread does not produce a crackling sound as it cools, it is a sign that your crust is either too hard (dry and thick crust), or too chewy (wet crust).
Depending on what your ideal crust texture is, a sourdough bread that does not crackle could or could not be an issue.
Some people like a slightly hard and chewy crust texture, and therefore it would be normal if your sourdough bread does not crackle when it is cooled. However, if you like a thin and crispy crust, you would want a long and extended crackling sound as your baked sourdough bread is taken out of the oven to be cooled.
The micro cracking of the crust during cooling also helps to improve the crispiness of the crust. The micro cracks helps to weaken the crust slightly and improving its brittleness; we only have to apply a light chewing force to split the crust, and hence we get a sense of crispiness in the bite.
How to get sourdough bread to crackle more?
The crust gets weaker and more brittle if it is drier and thinner; a drier and thinner crust crackles more as it is cooled, and it is an indicator of crispiness.
I have written an extensive article titled ‘Secrets to Thin and Crispy Sourdough Crust’ that looks into how gluten development, baking time and steaming helps crust to remain dry, thin and crispy.
