In enology, “volatile acidity” (VA) primarily refers to the formation of which defect and is chiefly associated with which microorganism?

Introduction / Context:
Volatile acidity (VA) is a key quality metric in wine. Excess VA indicates spoilage characterized by elevated acetic acid and often ethyl acetate, which smell like vinegar and nail-polish remover, respectively. Identifying its microbial source is essential for prevention and remediation.

Given Data / Assumptions:

• VA is measured as volatile acids, chiefly acetic acid; sometimes expressed as acetic acid equivalents.
• Oxygen exposure favors acetic acid bacteria activity.

Concept / Approach:
Acetobacter and related acetic acid bacteria oxidize ethanol to acetic acid when oxygen is present. They can also contribute to ethyl acetate formation. VA is distinct from total acidity and fixed acidity; it specifically captures volatile components that distill with steam.

Step-by-Step Solution:

Verification / Alternative check:
Winery analyses and regulations often set VA limits; elevated VA correlates with AAB contamination and oxygen exposure.

Why Other Options Are Wrong:

• Total acidity/fixed acidity: different metrics from VA.
• Brettanomyces: associated with barnyard, clove, medicinal notes; not the primary cause of VA spikes.
• Mousy aroma alone: linked to other spoilage pathways, not the definition of VA.

Common Pitfalls:
Confusing sensory faults from Brettanomyces with the chemical definition of VA; assuming all acidity increases are volatile.

Final Answer:
Produced by Acetobacter (acetic acid bacteria) leading to acetic acid/ethyl acetate