Sourdough bread is a naturally leavened bread that’s fermented using a sourdough starter—a living culture of wild yeast and beneficial bacteria mixed with flour and water. Unlike commercial breads that rely on packaged yeast for a quick rise, sourdough undergoes a slow fermentation process, often taking 12-24 hours or more, which develops its signature tangy, slightly sour flavor from lactic acid production. The crumb (interior) is typically chewy and open with irregular air holes, while the crust is thick, blistered, and deeply caramelized for a satisfying crunch. It’s usually made with simple ingredients like flour, water, and salt..