What is the effect of Acetobacter in brewing?

Acetobacter is a genus of bacteria that primarily converts ethanol into acetic acid, leading to a sour flavor in beverages such as beer and wine. When present in the brewing process, especially if conditions are not properly controlled, Acetobacter can thrive and produce vinegar-like sourness, which is an undesired outcome in most traditional beer styles but can be intentionally sought in sour beers.

The sour notes resulting from Acetobacter are particularly noticeable during fermentation when there is residual sugar available for the bacteria to metabolize. Thus, the ability of Acetobacter to produce acetic acid significantly alters the flavor profile of the beer, making it distinctly more tart or sour.

While Acetobacter does not contribute to sweetness, carbonation, or alcohol production in a beneficial way for most brewing practices, it certainly impacts the sensory attributes of the final product, chiefly through the introduction of sourness.