Sourdough’s characteristic tang comes from the organic acids produced during fermentation by lactic acid bacteria and yeast. Wild microbes in a starter break down sugars in flour and generate a mix of lactic acid and acetic acid, along with carbon dioxide and flavor compounds. The balance between these acids—more lactic for a mild, creamy sourness, more acetic for a sharp, vinegar-like bite—defines the perceived tanginess.
Microbes and acids
The sourdough ecosystem is dominated by lactic acid bacteria such as Lactobacillus species and various wild yeasts. Jan De Vuyst at Katholieke Universiteit Leuven has described how heterofermentative lactic acid bacteria produce both lactic and acetic acids together with ethanol and carbon dioxide, creating the complex acid profile of sourdough. Certain strains like Lactobacillus sanfranciscensis are historically associated with pronounced sour notes in regional breads, illustrating how microbial composition shapes taste. Starter ecology, the particular community of microbes maintained by feeding schedule and local environment, therefore has outsized influence on tang.
Baking choices that shape tang
Fermentation conditions steer which acids dominate. Cooler fermentation and lower hydration tend to favor pathways that produce more acetic acid, increasing sharpness, while warmer, wetter fermentations encourage lactic acid production and a milder sourness. Michael Gänzle at the University of Alberta has examined how temperature, water content, and substrate availability alter metabolic pathways in sourdough microbes and thus the aroma and acidity of the final loaf. Bakers also influence acid balance through starter maintenance: frequent refreshments tend to keep acidity lower, while longer ages between feedings allow acids to accumulate. Flour type matters too, because whole-grain flours supply different sugars and buffering minerals that change microbial activity and flavor intensity.
Acidity has practical consequences beyond taste. A more acidic dough improves shelf life because low pH inhibits spoilage molds and some bacteria, reducing the need for chemical preservatives. Marco Gobbetti at the University of Bari has shown that sourdough fermentation also reduces phytic acid in whole grains, which can increase mineral bioavailability and affect digestibility. These nutritional effects are part of why many traditional cultures favored long fermented breads.
Cultural and territorial factors enter through microbial biogeography and baking traditions. San Francisco–style sourdough is often cited for its tang both because local starters historically favored acetic-producing bacteria and because cooler coastal climates and long fermentations supported that metabolism. Elsewhere, warmer inland traditions yield different sourness profiles. Home bakers and artisan bakers alike can tune tang by adjusting hydration, temperature, starter age, and flour choice, making sourdough a living expression of local ingredients, techniques, and climate.
Understanding the microbial causes and the baker’s levers for control clarifies why sourdough tang varies so widely. The interplay of microbial ecology, fermentation conditions, and grain composition produces the acids that define sourdough’s distinctive flavor, while also shaping texture, preservation, and nutritional outcomes. That combination of science and craft is why sourdough remains both a subject of research and a central element of baking culture.