Yeast in Food Production (Edexcel IGCSE Biology)
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
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