On Food and Cooking

modern sourdoughs, and bread in much of the
world is made with sourdough starters that
give distinctive regional flavors. The bacteria
somehow delay starch retrogradation and
staling, and the acids they produce make the
bread resistant to spoilage microbes: so
sourdough breads are especially flavorful and
keep well. Because browning reactions are
slowed in acid conditions, sourdough breads
tend to be lighter in color than straight yeast
breads, and their flavor less toasty.
It isn’t easy to make good bread with
sourdough cultures. There are two reasons for
this. One is that the bacteria grow faster than
the yeasts, almost always outnumber them by
factors of a hundred or a thousand, and inhibit
the yeasts’ gas production: so sourdoughs
often don’t rise very well. The other is that
acid conditions and bacterial protein-digesting
enzymes weaken the dough gluten, which
makes it less elastic and the resulting bread
more dense.