Metabolism in yeasts: Which fermentation pathway do yeasts commonly perform under anaerobic conditions relevant to food and beverage production?

Introduction / Context:
Yeasts are central to baking, brewing, and winemaking because of their capacity to convert sugars into ethanol and carbon dioxide. Recognizing their dominant fermentation route is essential for understanding leavening, alcohol production, and flavor development.

Given Data / Assumptions:

• Typical brewery/winery yeast: Saccharomyces cerevisiae (and relatives).
• Anaerobic metabolism in these yeasts leads primarily to ethanol and CO2.
• Lactic fermentations are typically bacterial (e.g., Lactobacillus), not yeast-driven in standard processes.

Concept / Approach:
The Embden–Meyerhof–Parnas pathway yields pyruvate, which yeast decarboxylate to acetaldehyde and then reduce to ethanol while regenerating NAD+. This defines alcoholic fermentation. While a few yeasts can produce small amounts of lactic acid, the terms “homolactic” and “heterolactic” describe bacterial pathways.

Step-by-Step Solution:
Identify the common industrial role of yeasts (ethanol and CO2 production). Associate that role with alcoholic fermentation. Exclude homolactic and heterolactic fermentations as bacterial specializations. Choose “Alcoholic fermentation.”

Verification / Alternative check:
Fermentation balances in breweries and bakeries show ethanol and CO2 as principal products of yeast anaerobic metabolism.

Why Other Options Are Wrong:
Homolactic and heterolactic pathways are characteristic of lactic acid bacteria; “all” would incorrectly include bacterial routes; propionic fermentation is linked to Propionibacterium.

Common Pitfalls:
Assuming all fermentations are interchangeable across microbes; metabolic end products and pathways are organism-specific.

Final Answer:
Alcoholic fermentation.