Question

What is the primary gas responsible for the leavening effect in bread when yeast ferments sugars?

• A. Carbon dioxide
• B. Nitrogen
• C. Oxygen
• D. Helium

Answer 1

Answer:

A. Carbon dioxide

Yeast Fermentation and Bread Leavening

The Chemical Process:

• Yeast, a single-celled fungus, consumes sugars present in bread dough.

• Through a process called anaerobic respiration (fermentation), yeast converts these sugars into ethanol (alcohol) and carbon dioxide (CO2).

• The chemical equation for this fermentation process is: C6H12O6 (sugar) → 2 C2H5OH (ethanol) + 2 CO2 (carbon dioxide) + Energy.

The Leavening Effect:

• The carbon dioxide gas produced is trapped within the gluten network of the dough.

• As more CO2 is generated, it forms small bubbles, causing the dough to expand and rise.

• This expansion is known as leavening, which gives bread its light and airy texture.

Factors Influencing Fermentation:

• Temperature: Yeast activity is optimal between 75-80°F (24-27°C). Higher temperatures can kill yeast, while lower temperatures slow down fermentation.

• Sugar Availability: Yeast requires sugars to ferment. The type and amount of sugar in the dough affect fermentation speed.

• Yeast Strain: Different strains of yeast have varying fermentation rates and produce different flavor profiles.