How yeast fermentation works in bread making

Quick Takeaway: Yeast eats sugar and produces CO₂ gas and alcohol. The gas makes bread rise, while alcohol evaporates during baking. Temperature and time control the process.

The Fermentation Process

Yeast (Saccharomyces cerevisiae) performs alcoholic fermentation: 1. Consumes sugar (glucose, fructose, maltose) 2. Produces CO₂ gas (makes bread rise) 3. Produces alcohol (evaporates during baking) 4. Produces flavor compounds (creates bread's taste)

Chemical Equation

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy (Glucose → Alcohol + Carbon Dioxide + Energy)

Temperature Effects

- 60-70°F (15-21°C): Slow fermentation, more flavor development - 75-85°F (24-29°C): Optimal speed, balanced flavor - 90°F+ (32°C+): Fast fermentation, less flavor, can kill yeast - Below 40°F (4°C): Yeast becomes dormant

Types of Yeast

- Active dry: Needs rehydration, longer shelf life - Instant: Can be mixed directly with flour - Fresh: Perishable, most flavorful - Sourdough starter: Wild yeast + bacteria, complex flavors

Fermentation Stages

1. Bulk fermentation: First rise, develops flavor and structure 2. Punch down: Redistributes yeast and temperature 3. Proofing: Final rise, prepares for baking 4. Oven spring: Final expansion in hot oven

Signs of Proper Fermentation

- Volume increase: Dough doubles in size - Surface bubbles: Small bubbles on dough surface - Finger test: Dough springs back slowly when poked - Aroma: Pleasant, slightly alcoholic smell

Common Problems

- Over-proofed: Dough collapses, sour taste - Under-proofed: Dense bread, raw flour taste - Too hot: Yeast dies, no rise - Too cold: Very slow rise, may not double