Ethanol can be produced by the fermentation of sugar solutions using yeast. Describe the conditions needed for fermentation and explain why ethanol produced this way is considered a renewable fuel, unlike fuels produced from crude oil.

1. Yeast (Saccharomyces cerevisiae) is required as the organism that carries out the fermentation.
2. The temperature must be warm but not too hot – typically 30–35 °C – to optimise yeast activity.
3. The process must be anaerobic; oxygen must be absent so that yeast produces ethanol rather than oxidising it.
4. Crude oil is a finite, non‑renewable resource that takes millions of years to form and cannot be replenished on a human timescale.
5. Ethanol from fermentation is renewable because the sugars or crops used (e.g. sugarcane, corn, wheat) can be regrown each year, providing a continuous supply.