Yeast in Food Production (Edexcel IGCSE Biology (Modular)) : Revision Note

Yeast in Food Production

• Microorganisms can be used by humans to produce foods and other useful substances

• One example of this is the production of bread using yeast

• Yeast is a single-celled fungus that can carry out both aerobic and anaerobic respiration

Yeast is a single-celled fungus, similar to the one shown in the diagram above

Making bread

• During bread making yeast is added to bread dough

• The yeast produces enzymes that break down the starch in flour, releasing sugars that can be used by the yeast in respiration

  • The yeast begin to respire aerobically but will switch to anaerobic respiration when oxygen runs out

• When yeast carries out anaerobic respiration it produces alcohol (ethanol) and carbon dioxide

• The carbon dioxide produced by the yeast is trapped in small air-pockets in the dough, causing the dough to rise (increase in volume)

• The dough is then baked in a hot oven to form bread

  • During baking any ethanol produced by the yeast is evaporated in the heat, so bread doesn't contain any alcohol

• The yeast is killed by the high temperatures used during baking

  • This ensures there is no further respiration by the yeast

The carbon dioxide produced by the anaerobic respiration of glucose is what makes bread dough rise