Yeasts are single-celled microorganisms that are biologically classified as fungi. Although there are hundreds of different species of yeast, the best-known is Saccharomyces cerevisiae or baker's yeast. Along with several other species, this yeast uses carbohydrate as a source of food, converting it to carbon dioxide and alcohol in the process known as fermentation. Yeasts occur naturally in the environment, and can be encouraged to grow and reproduce to provide natural leavens.

Want to find out more? Look at the chapter on ingredients in the book flour and water.

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