Making ethanol by fermentation
5 marks · HardA chemical company wants to maximise ethanol production using fermentation.
Describe how yeast, glucose solution, and temperature are used to maximise ethanol production in this process.
Explain why the mixture is kept in the absence of air.
Suggest what would happen if the temperature during fermentation reaches 50°C. Give a reason for your answer.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Yeast is added to a glucose (or sugar) solution; the mixture is kept at 30–40°C to provide optimum temperature for enzyme activity. · must show Yeast and glucose solution, Optimum temperature given as about 30–40°C
(b) To prevent oxygen from allowing aerobic respiration which would reduce ethanol yield. · must show Air would lead to aerobic respiration OR no ethanol formed
(c) Fermentation would stop because enzymes in yeast become denatured or lose activity at high temperatures (e.g. 50°C). · must show Enzymes denatured, Fermentation stops or slows greatly
Common mistakes: Saying yeast produces ethanol in air; Ignoring enzyme denaturation at high temperature
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States yeast is added to glucose or sugar solution
B2 (a) · 1 mark · Gives a correct temperature range (30–40°C) or describes optimum temperature for enzyme activity
B3 (b) · 1 mark · Explains absence of air prevents aerobic respiration or ensures ethanol is produced
B4 (c) · 1 mark · States that enzymes are denatured or activity is lost at high temperature (e.g. 50°C)
A1 (c) · 1 mark · Links denaturation to fermentation stopping or reduced ethanol yield
Worked solution
a) To maximise ethanol production, yeast is added to a glucose solution and kept at an optimum temperature between 30°C and 40°C. This ensures enzymes in the yeast work efficiently to convert glucose to ethanol.
b) The mixture is kept in the absence of air to prevent aerobic respiration, which would convert glucose into carbon dioxide and water, not ethanol.
c) At 50°C, enzymes in the yeast would denature, stopping fermentation because the enzymes lose their structure and function at high temperatures.