Wine spoilage nomenclature – “tourne”: In traditional enology, the spoilage most commonly occurring in wine called “tourne” refers to which process?

Introduction / Context:
Classical French enological terminology identifies several “piqûres” and faults. “Tourne” broadly denotes wine that has “turned,” typically due to bacterial growth leading to acidity and off-odors. Recognizing the underlying metabolism helps winemakers diagnose and intervene.

Given Data / Assumptions:

• Residual sugars can support spoilage bacteria if SO2, pH, and storage are not properly managed.
• Common organisms include lactic acid bacteria and other heterofermenters.
• The question asks specifically about acid formation from sugars.

Concept / Approach:
“Tourne” is commonly tied to bacterial souring where fermentable sugars are converted into organic acids (lactic, acetic), elevating volatile acidity and dulling fruit character. While oxidative defects exist, the paradigmatic “tourne” points to sugar-driven acidification under poor hygiene or inadequate SO2, not primarily oxidation of aldehydes/ketones.

Step-by-Step Solution:
Identify that the fault involves increased acidity and bacterial growth. Note the availability of glucose/fructose as substrates. Select the option that names acid formation from sugars via bacterial souring.

Verification / Alternative check:
Cellar records of affected wines show rising volatile acidity and lactic/acetic profiles alongside residual sugar consumption; corrective blending or sterile filtration is often required.

Why Other Options Are Wrong:
Oxidative aldehyde pathways give flat/sherry-like notes but are not the canonical “tourne.”

Both – overbroad; the term is used most for sugar-based bacterial souring.

None/acetaldehyde-only – do not capture the core defect.

Common Pitfalls:
Confusing “piqûre lactique” and acetification; both raise acidity but have different drivers and sensory signatures.

Final Answer:
Acid formation from sugars (e.g., glucose and fructose) via bacterial souring.