Fermentation Flashcards

All 6 cards in this deck

What are the steps to make ethanol by fermentation?
e.g. from a glucose solution

1. Dissolve the carbohydrate (glucose) in warm water
2. Add yeast, keep at about 30 °C and exclude air
3. Leave to ferment: glucose → ethanol + carbon dioxide, then filter off the yeast

What is the word equation for the fermentation of glucose?

glucose → ethanol + carbon dioxide
$\mathrm{C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2}$

What is the role of yeast in fermentation?

It provides the enzymes (zymase) that catalyse the conversion of the carbohydrate into ethanol.

Why is fermentation carried out at about 30 °C rather than 80 °C?

At 80 °C the enzymes in the yeast are denatured, so they no longer work; at about 30 °C they are most effective.

What are the steps to obtain a more concentrated ethanol solution from a fermentation mixture?
e.g. distilling a dilute ethanol–water mixture

1. Heat the mixture in a flask with a fractionating column
2. Ethanol (boiling point 78 °C) evaporates first as it boils below water (100 °C)
3. Condense the vapour at about 78 °C and collect this ethanol-rich distillate

True or false? Fermentation on its own can produce pure ethanol.

False. It gives only a dilute solution (around 10–15% ethanol), so fractional distillation is needed to concentrate it.