Cambridge O Level Biology · Syllabus 5090 · Biotechnology and Genetic Modification
Fermentation
What is Fermentation?
The use of microorganisms to make a useful product. In yeast, fermentation is anaerobic respiration: glucose is converted to ethanol and carbon dioxide, and energy is released, without oxygen being used. The same reaction supports two industries that want opposite products from it - bread making, which uses the carbon dioxide to raise dough, and ethanol production, which collects the ethanol. In industrial usage the word also describes the growth of microorganisms in a fermenter, a process that may be aerobic or anaerobic depending on the organism and the product required.
This definition is part of the Biotechnology and Genetic Modification chapter in Cambridge O Level Biology.
Common mistakes with Fermentation
- “All industrial fermentation is anaerobic.” Why wrong Many fermenters have a sterile air inlet precisely because the organisms inside them respire aerobically. If oxygen were never wanted, the inlet would not exist.
- “All fermentation is anaerobic.” Why wrong True of yeast fermentation, but an industrial fermenter is a vessel, not a process, and many processes run in one are aerobic — which is why the sterile air inlet exists. Say instead In yeast, fermentation is anaerobic respiration. In a fermenter, whether oxygen is supplied depends on the organism and the product.
Questions students ask about Fermentation
What happens to the yeast and the ethanol during baking?
Baking kills the yeast, so fermentation stops, and most of the ethanol evaporates. The heat also sets the structure of the dough so that the risen shape becomes permanent.
Is industrial fermentation always anaerobic?
No. In yeast, fermentation means anaerobic respiration, but an industrial fermenter is a vessel rather than a single process, and many processes run in one are aerobic and need sterile air supplied through a sparger. Whether oxygen is supplied depends on the organism and the product wanted.