Bread yeast works by acting as a leavening agent, causing bread to rise by converting sugars in the dough into carbon dioxide and ethanol.
Here's a more detailed explanation of the process:
1. Yeast as a Living Organism:
- Baker's yeast is a single-celled microorganism, specifically strains of Saccharomyces cerevisiae. It's alive and needs food, moisture, and warmth to thrive.
2. Fermentation: The Key Process
- Yeast's primary function in bread making is fermentation. Fermentation is an anaerobic process, meaning it occurs without oxygen.
- Yeast consumes the fermentable sugars (like glucose, fructose, and maltose) present in the flour. These sugars are naturally present in the flour, and some are created when enzymes in the flour break down starches.
3. The Products of Fermentation:
- Carbon Dioxide (CO2): This is the gas that causes the dough to rise. The yeast produces CO2 as it consumes the sugars. The gluten network in the dough traps the CO2 bubbles, causing the dough to expand.
- Ethanol (Alcohol): Ethanol is also produced during fermentation. Most of the ethanol evaporates during baking due to the high temperatures.
- Flavor Compounds: Yeast also produces a variety of other organic compounds that contribute to the characteristic flavor and aroma of bread.
4. The Rising Process:
- As the yeast ferments, it produces carbon dioxide.
- The gluten in the flour, which is developed through kneading, forms a stretchy network that traps these gas bubbles.
- This trapped gas causes the dough to expand in volume, resulting in the characteristic "rise" of bread.
5. The Baking Process:
- During baking, the yeast's activity increases initially due to the rising temperature.
- Eventually, the temperature becomes too high, and the yeast dies.
- The ethanol evaporates, and the gluten network sets, giving the bread its final structure. The carbon dioxide bubbles create the airy texture.
In summary, bread yeast consumes sugars in dough, producing carbon dioxide that leavens the bread, creating its light and airy texture, and also contributing flavor compounds.
