Sourdough bread is a type of bread that is leavened using sourdough starter. It has a caracteristic sour taste and aroma, and a thick and crusty crust, result of the high moisture content in the dough. It was the most common form of bread in the Middle Age. Today, it is seen as an alternative to regular bread made out of commercial yeast, as its flavor is a lot more complex. This process of breadmaking is very slow and time-consuming, due to the time that the sourdough starter requires to ferment, which results in a very distinctive and irregular crumb structure.