Kinetics of alcoholic fermentation by Saccharomyces cerevisiae: Under standard batch conditions after inoculation, ethanol production becomes measurably detectable within approximately how many hours?

Introduction / Context:
In ethanol fermentations using Saccharomyces cerevisiae, the time to detectable ethanol depends on inoculum size, sugar concentration, temperature, and aeration strategy. A typical benchmark question asks when ethanol production is first evident in a standard batch.

Given Data / Assumptions:

• Conventional batch at about 30 °C with a reasonable inoculum.
• Glucose or molasses substrate with minimal oxygen (facultative anaerobic metabolism).
• Detectable ethanol by routine assays (for example, GC or enzymatic kits).

Concept / Approach:
After a short lag, yeast enters exponential growth and begins active glycolysis. Ethanol production accompanies growth under oxygen-limited conditions. Many teaching references cite first measurable ethanol near the 12-hour mark for standard batches.

Step-by-Step Solution:

Verification / Alternative check:
Brewing and fuel ethanol training manuals often show initial ethanol detection within the first 8–16 hours; 12 h is a representative midpoint.

Why Other Options Are Wrong:

Common Pitfalls:
Forgetting how inoculum size and temperature shift timelines; higher inoculum or warmer conditions can shorten the time, while cooler or stressed conditions may delay it.

Final Answer:
12 h.