Sourdough Starter Fermentation

A sourdough starter is a simple mixture of flour and water that, over several days, becomes home to wild yeast and bacteria naturally present in the flour and surrounding air. Unlike bread made with commercial yeast, sourdough bread relies entirely on this wild culture to rise, which is why the same starter can behave differently depending on where it lives. Once a starter is established, it must be "fed" regularly -- discarding part of the mixture and adding fresh flour and water -- to keep the yeast and bacteria active. The yeast produces carbon dioxide gas, which gets trapped in the dough's gluten network and causes it to rise. The bacteria, meanwhile, produce lactic and acetic acid, giving sourdough bread its distinctive tangy flavor and also helping preserve the bread longer than yeast-only loaves. Bakers often name and maintain their starters for years, sometimes decades, passing portions to friends or family members. Because each starter's exact mix of microorganisms differs based on its environment and feeding schedule, no two starters produce identical bread, even when the same flour and technique are used. Some bakeries treat their starters as a kind of signature, guarding the recipe for maintaining it as closely as a trade secret.