On Food and Cooking

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:
C 6 H 12 O 6 2CH 3 CH 2 OH + 2CO 2 + 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