Optimising conditions for ethanol fermentation by Saccharomyces cerevisiae: Which combination of pH and temperature is most appropriate for high-yield ethanol production?
-
ApH 6; temperature 35 °C
-
BpH 5; temperature 35 °C
-
CpH 6; temperature 30 °C
-
DpH 5; temperature 30 °C
-
EpH 7; temperature 25 °C
Answer
Correct Answer: pH 5; temperature 30 °C
Explanation
Introduction / Context:Ethanol productivity depends strongly on pH and temperature. Saccharomyces cerevisiae generally prefers mildly acidic pH and moderate temperatures for robust fermentation and reduced contamination risk.
Given Data / Assumptions:
- Industrial ethanol fermentation using S. cerevisiae.
- Batch or fed-batch with glucose/molasses substrate.
- Goal: maximize yield and productivity while maintaining yeast health.
Concept / Approach:Typical optimal ranges are pH about 4.5–5.5 and temperature around 28–32 °C. pH near 5 discourages bacterial contaminants and supports yeast metabolism; 30 °C is a standard setpoint balancing rate and viability.
Step-by-Step Solution:
Match yeast optima to provided choices.Select pH 5 with 30 °C as the best combination.Exclude higher pH or higher temperature options that can impair performance or increase contamination.Verification / Alternative check:Brewing and fuel ethanol references commonly recommend pH ~5 and 30 °C for S. cerevisiae ferments.
Why Other Options Are Wrong:
pH 6 and/or 35 °C: shift away from common optima; may increase stress or contamination risk.pH 7; 25 °C: not typical for vigorous ethanol fermentation.Common Pitfalls:Running at too high a temperature; even small increases can raise by-product formation and reduce viability.
Final Answer:pH 5; temperature 30 °C.