Enology (wine fermentation) — Commercial alcoholic fermentation of grape must is carried out using selected strains of which microorganism?

Introduction / Context:
Wine fermentation converts sugars in grape must into ethanol, carbon dioxide, and aroma compounds. Controlled fermentations rely on starter yeasts chosen for robustness, predictable kinetics, and desirable sensory profiles. Knowing the correct organism prevents off-flavors and stuck fermentations.

Given Data / Assumptions:

• Substrate: grape must rich in glucose and fructose.
• Process: anaerobic/alcoholic fermentation at controlled temperatures.
• Goal: consistent alcohol content and varietal aroma expression.

Concept / Approach:
Saccharomyces cerevisiae is the standard wine yeast due to its ethanol tolerance, rapid sugar uptake, and favorable ester formation. The distractors include a lager beer yeast (often written as S. carlsbergensis/S. pastorianus), a bacterium (Bacillus subtilis) lacking alcoholic fermentation traits, and a lactic acid bacterium misnamed as “Pedicoccus” (properly Pediococcus), associated more with souring than primary alcoholic fermentation.

Step-by-Step Solution:

Verification / Alternative check:
Winemaking texts list numerous commercial S. cerevisiae strains (e.g., EC-1118, QA23) optimized for different grape varieties and temperatures.

Why Other Options Are Wrong:

• S. carlsbergenesis: lager brewing yeast; not the standard wine starter.
• B. subtilis: aerobic spore-former; not a wine fermenter.
• “Pedicoccus cerevisiae”: lactic bacterium; used in malolactic fermentation control, not primary alcohol production.

Common Pitfalls:
Confusing malolactic bacteria (which convert malic to lactic acid) with the yeast that ferments sugars to ethanol.

Final Answer:
Saccharomyces cerevisiae