How does sourdough bread get its tangy flavor?

Sourdough’s characteristic tang comes primarily from organic acids produced during fermentation by lactic acid bacteria and yeasts that live in the starter culture. Lactic acid gives a mild, rounded sourness while acetic acid produces the sharper, vinegar-like note. These acids accumulate as microbes metabolize sugars in flour, and the relative amounts of lactic and acetic acid determine whether a loaf tastes gently tangy or distinctly sharp. Maria De Vuyst Katholieke Universiteit Leuven has analyzed how the balance between these acids shapes sourdough flavor and stability, showing that microbial interactions and fermentation dynamics control acid production.

Microbiology of the Starter
A sourdough starter is a stable microbial ecosystem composed mainly of heterofermentative lactic acid bacteria and wild yeasts. Limosilactobacillus sanfranciscensis is a species often associated with pronounced sourdough flavors and the historical San Francisco type, and various Saccharomyces and Candida species contribute fermentative activity. Sergio Gänzle University of Alberta has described how lactic acid bacteria convert maltose and other sugars into lactic and acetic acids while yeasts produce carbon dioxide and flavor-active compounds such as alcohols and esters. These microbial metabolites interact, creating the complex aroma and taste profile recognized as sourdough.

Flavor Compounds and Fermentation
Beyond lactic and acetic acids, thousands of volatile and non-volatile compounds contribute to sourdough taste. Ethanol, aldehydes, organic acids, and amino-acid–derived compounds develop through proteolysis and Maillard reactions during baking. Marco Gobbetti University of Bari has investigated how proteolytic activity by certain bacteria releases free amino acids that are precursors to flavorful volatiles. Temperature, hydration, fermentation time, and the flour’s enzymatic composition shift metabolic pathways, favoring either lactic or acetic acid production and altering volatile profiles that influence perceived tanginess.

Relevance, Causes, and Consequences
Understanding sourdough acidity matters for bakers, nutritionists, and food systems. Acidity extends shelf life by inhibiting spoilage molds and some bacteria, reducing reliance on preservatives. Acid-driven changes in dough chemistry also influence gluten strength and crumb structure, affecting processability and consumer acceptance. Culturally, regional starters and local flour varieties create territorial identities: San Francisco sourdough, Eastern European rye breads, and Italian long-fermented loaves exemplify how local microbes and practices produce distinct tangs. Environmental conditions such as ambient temperature and humidity further shape starter communities, so similar recipes yield different flavors across locations.

Practical implications flow from this science. Bakers can manipulate hydration, fermentation temperature, feed schedule, and flour type to steer acid production and flavor, trading speed for acidity or vice versa. For communities, protecting traditional sourdough practices preserves culinary heritage and local microbial biodiversity. For public health and sustainability, sourdough’s potential to improve bread shelf life and modify nutrient availability invites further study; researchers continue to evaluate how fermentation affects digestibility and glycemic response. Grounded studies by De Vuyst, Gänzle, Gobbetti, and others provide the mechanistic foundation that explains why sourdough tastes tangy and how that tang reflects ecology, technique, and place.