You have decided to try to make your own wine by adding yeast to a sweet grape juice. After allowing plenty of time for the yeast to grow, you find that although the sugar levels in the juice are decreased, there is no alcohol in the mixture. What could have been the reason fermentation did not occur? A) More sugar needs to be added. Yeast need a lot of energy before it produces alcohol. B) Less sugar is needed in the juice. High sugar concentration causes cellular respiration to occur rather than fermentation. C) Yeast cannot ferment grapes, only bacteria can. D) The mixture needs less oxygen. Yeast only produces alcohol in the absence of oxygen. E) The mixture needs more carbon dioxide. Yeast produce alcohol more quickly in the presence of CO ₂.

Question

Quizplus · Accepted Answer

Yeast ferments sugars into alcohol in anaerobic conditions (absence of oxygen). If there is oxygen present, yeast will preferentially undergo aerobic respiration instead of fermentation, which does not produce alcohol.

You Have Decided to Try to Make Your Own Wine