Yeast has often been called the first “domesticated animal,” as they have been used in winemaking, beer making, and bread making for centuries. Yeast converts food into alcohol and carbon dioxide (CO2) during fermentation. In the manufacture of wine and beer, the yeast’s manufacture of alcohol is a desired and necessary component of the final product, with the CO2 giving beer and champagne their bubbly attributes. Bread making requires the production of CO2 by yeast, thus allowing certain doughs to rise. Yeasts used in brewing and baking are cultivated strains carefully kept to prevent contamination and used over and over; for example, certain bakers and bakeries make sourdough bread with yeasts that have been cultivated for tens of years. (For more about fermentation, see the chapters “Basics of Biology” and “Biology and You.”)