Making ethanol by fermentation
4 marks · NormalDescribe how ethanol can be made by fermentation of glucose.
State the main product formed if the fermentation is carried out in the presence of air.
Explain why the fermentation reaction is slow if the temperature is below 30°C.
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(a) Yeast is added to glucose solution and kept warm (about 30°C) in the absence of air. The yeast enzymes convert glucose to ethanol and carbon dioxide.
(b) Carbon dioxide and water
(c) Low temperatures slow down the activity of the enzymes (yeast enzymes work more slowly at lower temperature).
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Marking points
M1 (a) · 1 mark · Describes addition of yeast to glucose (or other sugar) in absence of air and kept warm.
M2 (a) · 1 mark · Mentions enzymes in yeast convert glucose into ethanol and carbon dioxide.
B1 (b) · 1 mark · States correct main products are carbon dioxide and water.
B2 (c) · 1 mark · Explains that enzyme action is slower at lower temperatures.
Worked solution
a) Ethanol is made by adding yeast to glucose solution and keeping it warm (about 30°C) in anaerobic conditions. The enzymes in the yeast convert the glucose to ethanol and carbon dioxide.
b) If air is present, the main products are carbon dioxide and water.
c) At low temperatures, the enzymes in yeast work more slowly so the fermentation is very slow.