On Food and Cooking

for energy, and produce carbon dioxide gas
and alcohol as by-products of that
metabolism. The overall equation for the
conversion that takes place in yeast cells is
this:
C 6 H 12 O 6 2C 2 H 5 OH + 2CO 2 (1 molecule of
glucose sugar yields 2 molecules of alcohol
plus 2 molecules of carbon dioxide)
In making beer and wine, the carbon dioxide
escapes from the fermenting liquid, and
alcohol accumulates. In making bread, both
carbon dioxide and alcohol are trapped by the
dough, and both are expelled from the dough
by the heat of baking.
In an unsweetened dough, yeasts grow on
the single-unit sugars glucose and fructose
and on the double-glucose sugar maltose,
which enzymes in the flour produce from
broken starch granules. A small amount of
added table sugar in a dough will increase
yeast activity, while a large amount decreases
it (see sweet breads, p. 546), as does added