Yeast is a living, microscopic, single-cell organism that, as it grows, converts its food (through a process known as fermentation) into alcohol and carbon dioxide. This trait is what endears yeast to winemakers, brewmasters and breadbakers. In the making of wine and BEER, the yeast's manufacture of alcohol is desired and necessary for the final product; and carbon dioxide is what makes BEER and CHAMPAGNE effervescent. The art of breadmaking needs the carbon dioxide produced by yeast in order for certain doughs to rise. To multiply and grow, all yeast needs is the right environment, which includes moisture, food (in the form of sugar or starch) and a warm, nurturing temperature (70Ã‚Â° to 85Ã‚Â°F is best).