On Food and Cooking

material surrounding them must be elastic
enough to contain it for that much time. Weak
doughs and runny batters can’t hold gas
bubbles for more than a few minutes, and are
therefore usually raised with a faster-acting
gas source. This is the role played by
chemical leavenings. These ingredients are
concentrated, and small differences in the
amount added can cause large variations in
the quality of the finished food. Too little
leavening will leave it flat and dense, while
too much will cause the batter to overexpand
and collapse into a coarse structure with a
harsh flavor.
Nearly all chemical leavenings exploit a
reaction between certain acidic and alkaline
compounds that results in the production of
carbon dioxide, the same gas produced by
yeast. The first chemical leavening was a
dried water extract of wood ash — potash,
mainly potassium carbonate — which reacts
with the lactic acid in a soured dough as