Yeast — bread and brewing
Same biology, different products. CO₂ for bread, ethanol for brewing.
Bread.
- Yeast added to dough.
- Yeast ferments SUGAR → CO₂ + ethanol.
- CO₂ TRAPPED in sticky dough → bubbles → DOUGH RISES.
- Baking kills yeast and EVAPORATES ethanol.
- Result: light, fluffy bread.
Beer + wine + spirits (brewing).
- Yeast added to sugar source: barley malt (beer) or grape juice (wine).
- Sealed tank → low O₂ → ANAEROBIC fermentation.
- Sugars → ETHANOL + CO₂.
- Ethanol stays in liquid → alcoholic drink.
- CO₂ may be retained for fizz (beer, sparkling wine) or released.
Why it stops:
- When ethanol reaches ~12-15%, it kills the yeast.
- That's the natural ceiling for fermented drinks.
- Spirits (vodka, whisky) are made by DISTILLING fermented liquid → much higher alcohol %.
Worked qualitative. Why does fresh dough taste a little ALCOHOLIC if you let it rise too long?
- Yeast keeps producing CO₂ AND ethanol.
- The longer the rise, the more ethanol accumulates.
- Some doesn't fully evaporate during baking.
- Slight alcoholic note in some breads (sourdough).
- Why kids' books cute idea of yeast 'eating sugar' is essentially correct.
Cambridge tip. Always state ANAEROBIC respiration for brewing, and mention BOTH products (ethanol AND CO₂).
- Bread: CO₂ rises dough.
- Brewing: ethanol stays in liquid.
- Both: anaerobic fermentation.
- Yeast killed by ~15% alcohol.