the normal function of our brain cells Yeast Cells of brewer’s yeast, Saccharomyces cerevisiae, as seen through an electron microscope Each is about 0.005 mm in diameter The cell at the upper right center is in the process of reproducing, and bears the scars of previous buddings Yeasts and Alcoholic Fermentation Yeasts are a group of about 160 species of single-celled microscopic molds Not all are useful: some cause the spoilage of fruits and vegetables, some cause human disease (for example, the yeast infection of Candida albicans) Most of the yeasts used in making bread and alcoholic drinks are members of the genus Saccharomyces, whose name means “sugar fungus.” We cultivate them for the same reason that we use particular bacteria to sour milk: they make foods resistant to infection by other microbes, and produce substances that are mainly pleasant to us Essential to the yeasts’ production of alcohol is their ability to survive on very little oxygen, which most living cells use to burn fuel molecules for energy, leaving behind only carbon dioxide and water In the absence of oxygen, the fuel can be broken down only partly The overall equation for the production of energy from glucose without oxygen goes like this: C6H12O6 2CH3CH2OH + 2CO2 + energy Glucose alcohol + carbon dioxide + energy Yeasts introduce a variety of other compounds into the grape juice or grain mash that contributes characteristic flavors For ... fuel molecules for energy, leaving behind only carbon dioxide and water In the absence of oxygen, the fuel can be broken down only partly The overall equation for the production of energy from glucose without oxygen goes... sour milk: they make foods resistant to infection by other microbes, and produce substances that are mainly pleasant to us Essential to the yeasts’ production of alcohol is their ability to survive on very little...albicans) Most of the yeasts used in making bread and alcoholic drinks are members of the genus Saccharomyces, whose name means “sugar fungus.” We cultivate them for the same reason that we use particular bacteria to