Lesson 13 ·Class 9 · Economic Importance of Bacteria and Fungi · Flow Lab
Fermentation
How yeast turns sugar into alcohol.
Yeast, sugar and no oxygen. Watch what the yeast does with it.
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🍇 Step 1 of 5 · Sugar solution
Grape juice or malted grain provides the sugar. Yeast is added.
C₆H₁₂O₆ --zymase--> 2C₂H₅OH + 2CO₂
30°C
Rate of fermentation 71%
Free play — step through the process at your own pace, and move the slider to see what changes. Switch to when you're ready to test yourself.
Fermentation is simply anaerobic respiration in yeast — the same equation, put to work.
What this lesson covers
Challenges to clear
- Advance to the products of fermentation.
- Push the temperature to 55 °C or more and read why brewers avoid it.
The task
Yeast, sugar and no oxygen. Watch what the yeast does with it.
What this lesson covers
- Sugar solution — Grape juice or malted grain provides the sugar. Yeast is added.
- Oxygen shut out — The vessel is sealed. Without oxygen the yeast must respire anaerobically.
- Zymase acts — The enzyme zymase in yeast breaks the sugar down.
- Alcohol and CO₂ — Ethyl alcohol and carbon dioxide are produced. The bubbles you see are the CO₂.
- The yeast stops itself — Above roughly 14% alcohol the yeast is killed by its own product, so fermentation halts.
- C₆H₁₂O₆ --zymase--> 2C₂H₅OH + 2CO₂
- Too cold — the yeast is sluggish and fermentation nearly stops.
- Too hot — zymase is denatured and the yeast dies.
Hint
Fermentation is simply anaerobic respiration in yeast — the same equation, put to work.