Sourdough gets its sour taste mainly from the lactic acid bacteria present in the sourdough starter, which produce organic acids such as lactic acid and acetic acid during fermentation. These acids give sourdough its signature tangy and sometimes sharp flavor. The sourness level can be influenced by factors such as fermentation time, temperature, flour type, and starter maintenance.

Key Factors Making Sourdough Sour

• Lactic Acid and Acetic Acid: Lactic acid provides a mild, yogurt-like tang, while acetic acid gives a sharper, vinegar-like sourness.
• Natural Fermentation: Wild yeast and lactic acid bacteria ferment the dough, producing these acids.
• Fermentation Time: Longer fermentation allows more acid production, increasing sourness.
• Temperature: Warmer temperatures favor lactic acid bacteria, producing a milder sourness; cooler temperatures encourage acetic acid, resulting in a sharper taste.
• Flour Type: Whole grains and rye flour promote more bacterial activity and thus a more sour flavor.
• Starter Management: Using a mature starter or letting it become more acidic by delaying feedings can increase sourness.

In summary, the sourness comes from the acids produced by bacteria during fermentation, and bakers can adjust sourness by controlling fermentation time, temperature, flour choice, and starter handling.