Many yeasts (unicellular fungi), bacteria, and molds are used in food production. The oldest application of biotechnology used by mankind is probably the fermentation of fruit juice into wine. Under suitable conditions, a yeast can cause sugar-containing liquid to ferment. Lactic acid bacteria are used in the production of yoghurts and cheeses, which, as they divide, ferment the milk appropriately.

Baking yeast is an example of biotechnology. It is a fungus that breaks down the sugars in bread dough and and makes the dough fluffy by producing carbon dioxide.