from a root word that meant “to seethe,
boil, bubble over.” This derivation
underlines the way in which fermentation
seemed to be a kind of cooking of the
cereal gruel, a transformation from within.
The yeasts are a group of microscopic
single-celled fungi, relatives of the
mushrooms. More than 100 different species
are known. Some cause human infections,
some contribute to food spoilage, but one
species in particular — Saccharomyces
cerevisiae, whose name means “brewer’s
sugar fungus” — is put to good use in both
brewing and baking. For much of human
history, yeast was simply recruited from the
grain surface or supplied by an earlier piece of
dough, or obtained from the surface of beer
brewing vats. Today strains especially
selected for breadmaking are grown on
molasses in industrial fermentation tanks.
Yeast Metabolism Yeasts metabolize sugars