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Chemistry · Organic · Fermentation
Fermentation of glucose to ethanol
Yeast cells digest glucose ANAEROBICALLY to make ethanol and carbon dioxide. CO₂ is detected as it bubbles through limewater. After a week, the mixture is distilled to concentrate the ethanol.
Word equation
C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂
Catalysed by enzymes (zymase) in yeast. Optimum 25–37 °C. No oxygen allowed — keep the air-lock sealed.
Exam-style questions
1. Word equation for fermentation:
2. Why must AIR be EXCLUDED from the fermentation vessel?
3. After fermentation, dilute ethanol can be concentrated by distillation. Why does the ETHANOL come off FIRST?
4. Fermentation stops once the alcohol concentration in the mixture reaches about 15 %. Why?