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Microorganisms, food and fermenters
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Yeast and bacteria help make bread and yoghurt. Industrial fermenters grow microorganisms on a huge scale.
Yeast and bread
Dough contains flour, water, sugar and yeast.
Yeast respires, producing carbon dioxide. The gas is trapped in the dough, making it rise.
In anaerobic respiration yeast also makes ethanol, which evaporates when the bread is baked. Baking also kills the yeast.
Practical: measure carbon dioxide from yeast and sugar solution (count bubbles or measure gas volume) at different temperatures or sugar concentrations.
Yeast respires, producing carbon dioxide. The gas is trapped in the dough, making it rise.
In anaerobic respiration yeast also makes ethanol, which evaporates when the bread is baked. Baking also kills the yeast.
Practical: measure carbon dioxide from yeast and sugar solution (count bubbles or measure gas volume) at different temperatures or sugar concentrations.
Lactobacillus and yoghurt
Milk is pasteurised (heated to kill other microorganisms), then cooled to about 40 °C.
*Lactobacillus* bacteria are added and the milk is kept warm.
The bacteria ferment lactose (milk sugar) into lactic acid. The acid lowers the pH, which thickens the milk, gives a sour taste and helps stop other microorganisms growing.
*Lactobacillus* bacteria are added and the milk is kept warm.
The bacteria ferment lactose (milk sugar) into lactic acid. The acid lowers the pH, which thickens the milk, gives a sour taste and helps stop other microorganisms growing.
Industrial fermenters
Why does a fermenter need a water jacket?
- Microorganisms respire and release heat.
- Without cooling the temperature would rise above the optimum and enzymes would denature.
- Cold water flowing in the jacket removes the heat.
Answer: To remove heat released by respiring microorganisms and keep the optimum temperature.
Yeast produces carbon dioxide that makes bread rise. Lactobacillus turns lactose into lactic acid to make yoghurt. Fermenters need aseptic conditions, nutrients, optimum temperature and pH, oxygen and stirring.
The interactive lesson includes the diagrams for this topic.
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