Fermentation is the process by which certain microorganisms, including yeast and some bacteria, metabolise sugars and expel waste products such as carbon dioxide, ethanol and various forms of acid. In simple terms, it is the equivalent of digestion in humans and animals. Yeast fermentation is what causes bread dough to rise and is used in the production of alcoholic drinks. Bacterial fermentation is used to make foods such as yoghurt and sauerkraut, and in sourdough bread.

Want to find out more? Look at the chapter on rising, proving and fermentation in the book flour and water.

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