Optimising conditions for ethanol fermentation by Saccharomyces cerevisiae: Which combination of pH and temperature is most appropriate for high-yield ethanol production?

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:

Verification / Alternative check:
Brewing and fuel ethanol references commonly recommend pH ~5 and 30 °C for S. cerevisiae ferments.

Why Other Options Are Wrong:

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.