Sourdough’s tangy flavor comes primarily from organic acids produced during fermentation by a living community of microbes in the starter. Lactic acid bacteria and wild yeasts metabolize flour sugars and produce lactic acid and acetic acid alongside carbon dioxide and ethanol. The balance between these acids—milder lactic versus sharper acetic—determines whether a loaf tastes gently sour or brightly tangy.
Microbes and chemistry
Maria De Vuyst at KU Leuven and Marco Gobbetti at the University of Parma have reviewed how interactions between bacteria and yeast drive sourdough flavor development. Lactic acid bacteria such as Lactobacillus species convert sugars and some starch breakdown products into lactic acid. Certain heterofermentative lactobacilli also produce acetic acid when alternative electron acceptors and metabolic pathways are engaged. Wild yeasts contribute indirectly by producing metabolites and altering the dough environment, which affects bacterial pathways. Lactobacillus sanfranciscensis, a species often associated with traditional San Francisco starters, is one example of a bacterium linked to a characteristic bright, tangy profile in that regional style.*
Temperature, hydration and feeding schedule shift microbial metabolism. Cooler, firmer doughs and less frequent feeding tend to favor production of acetic acid, which gives a sharp, vinegar-like note. Warmer, wetter fermentations favor lactic acid and yield a milder, yogurt-like sourness. These mechanistic relationships are explained in the fermentation literature by De Vuyst and by Gobbetti, who emphasize metabolic flexibility in starter communities.
Practices, cultural identity, and consequences
Bakers’ choices create regional and household signatures. In San Francisco, historic practices and local microbes produced a nationally recognized tang; in parts of Europe, longer, warmer retardations produce softer sourness in country loaves. Because starters are passed down and maintained in specific environmental conditions, sourdough flavor is also a form of culinary heritage—microbial terroir shaped by flour type, water, ambient temperature and human routine.
Acidity has practical consequences beyond taste. The acids lower dough pH, which slows spoilage organisms and extends shelf life without chemical preservatives. Marco Gobbetti at the University of Parma has described benefits of sourdough fermentation for texture and nutritional quality, including partial degradation of phytic acid by microbial phytases, which can improve mineral bioavailability. Conversely, excessive acidity can mask subtle cereal flavors and is sometimes undesirable in certain baked products, so bakers balance fermentation to match consumer expectations.
Understanding sourdough’s tang therefore requires microbiology, chemistry and cultural context. The same microbial processes that create a desirable bright note also influence preservation, nutrition and regional identity, making sourdough both a biochemical phenomenon and a living culinary tradition.