days when even the petunias wilt in the heat, there's
some sense in cooling wine quickly! But gosh, it's annoying
when it freezes and pops the cork, something many of
us have done on a sweltering day.
wine contains alcohol, it's also mostly water, so when
the temperature of the bottle reaches 39° F (4°
C) molecules in the water begin to associate with each
other in a very precise arrangement. At 32° F (0°
C) a lattice of crystals begins and the fretwork of
empty spaces between the crystals means ice takes up
more room than water. In fact, ice occupies 1/11 more
space than the water from which it was formed.
While freezing point of wine depends primarily on its
percentage of alcohol, it is generally thought to be about
15°F (minus 10°C). Because the freezing point
of alcohol is lower than water, wine seldom freezes solidly—unless
of course you leave it for a long while in the freezer.
Nonetheless, the expansion of frozen water in wine exerts
considerable pressure on the bottle, and the escape route
is of course, the cork. And so it pops in response to
the pressure! Occasionally the bottle even cracks.
Just to make you feel a little cooler while reading this
answer, there's a wonderful story about a watercolor artist,
whose passion was painting scenes in the icy Arctic. One
recurring problem, however, was that his water for painting
often froze while working on a landscape. His creative
solution was to use vodka rather than water—a clever
use of the lower freezing point of alcohol, that kept
his paints and brushes pliable!
Sending our good wishes for wine that's nicely chilled,
Anne & Sue