Sourdough bread is a type of bread made from a naturally fermented mixture of flour and water, known as a sourdough starter. The starter contains wild yeasts and lactic acid bacteria that naturally occur in the flour and the environment, and they produce carbon dioxide gas as they feed on the flour's starches and sugars during fermentation. This process gives the bread its characteristic sour taste and chewy texture.
Unlike commercial yeast that is added to bread dough to make it rise quickly, sourdough bread is made by a slower fermentation process that can take several hours or even days. This long fermentation process allows for a more complex flavor to develop and also breaks down some of the gluten in the flour, making it easier to digest for some people who may be sensitive to gluten.
Sourdough bread has become popular in recent years as more people are interested in traditional, artisanal bread-making methods and the health benefits of fermented foods. It is also often preferred for its unique flavor and texture.