On Food and Cooking

controlled contact with oxygen, the wine goes
into impermeable glass bottles. For the last
two centuries, the standard stopper for wine
bottles has been cork, which is made from the
bark of a species of oak. Because cork can be
the source of off-flavors, some wine
producers are now using metal and plastic
stoppers (see box below).
Wine continues to be affected by oxidation
long after it leaves the cask. It picks up some
air when it is filled into the bottle, and the
bottle is sealed with a small space between
wine and cork. So while oxidation is greatly
slowed in the bottle, it does continue, though
it may be outweighed by a different set of
reactions, “reductive” rather than oxidative.
The chemical changes that occur are not well
understood, but include the ongoing liberation
of aromatic molecules from nonaromatic
complexes, and aggregation reactions among
tannins and pigments that further lower
astringency and cause a shift in pigment hues,