Kinetics of alcoholic fermentation by Saccharomyces cerevisiae: Under standard batch conditions after inoculation, ethanol production becomes measurably detectable within approximately how many hours?
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A10 h
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B12 h
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C15 h
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D24 h
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E48 h
Answer
Correct Answer: 12 h
Explanation
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:
Consider the lag and early exponential phases (several hours).Associate onset of vigorous glycolysis with ethanol generation.Select the commonly taught benchmark of ~12 h for detectable levels under typical conditions.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:
10 h / 15 h / 24 h / 48 h: possible under some conditions, but 12 h is the most widely cited rule-of-thumb for standard batches in education-oriented problems.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.