Sourdough fermentation is the process by which naturally occurring yeasts and bacteria interact with flour and water to leaven dough and develop its flavor. The key players are wild yeast and lactic acid bacteria. These microorganisms feed on sugars in the flour, producing carbon dioxide gas (which creates bubbles in the dough, causing it to rise) and various acids, including lactic and acetic acid, which contribute to the characteristic tangy flavor of sourdough bread. The fermentation process typically takes several hours to days, depending on factors like temperature, hydration, and the strength of the sourdough starter.