Yeast in brewing and baking: Higher Level only: This statement is Higher Level only. It builds on 3.2.9: yeast regenerates NAD by making ethanol instead of lactate.
Practise this as you read
- Outline how yeast is used in baking or brewing.
- Interpret data on yeast and temperature.
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The big idea: Without oxygen, yeast turns pyruvate into ethanol and carbon dioxide. Like lactate in muscle, this regenerates NAD so glycolysis continues. Bakers use the carbon dioxide; brewers use the ethanol.
The points to remember
- Glycolysis: glucose → 2 pyruvate, net 2 ATP, 2 reduced NAD.
- Pyruvate is decarboxylated: carbon dioxide is released.
- The product is reduced to ethanol by reduced NAD, so NAD is regenerated.
- Baking: carbon dioxide bubbles make dough rise; the ethanol evaporates in the oven.
- Brewing: the ethanol is the alcohol in beer and wine; the carbon dioxide gives the fizz.
Remember it as: Yeast without oxygen: bubbles for the baker, alcohol for the brewer.
Real example: bread and beer. Bread dough is left in a warm place to rise for an hour or so; beer is fermented for days, until the yeast has turned most of the sugar into ethanol.
Trap: Yeast makes ethanol and carbon dioxide, not lactate; humans make lactate and no carbon dioxide.
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How it is asked: Expect data on dough rising or gas released by yeast at different temperatures, and questions on what yeast produces and why it is used in baking and brewing.
IB-style questionOutline[3 marks]
Outline how anaerobic respiration in yeast is used in baking.
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