phase is boiling, in which we transform liquid
water into bubbles of water vapor, or steam.
Less obvious to the eye, because it’s so
gradual, is the evaporation of water at
temperatures below the boiling point. The
molecules in a liquid move with a wide range
of kinetic energies, and a small portion of the
molecules in room-temperature water are
moving fast enough to escape from the
surface and move into the air.
In fact, water molecules can even escape as
a gas from solid ice! This direct
transformation of a solid into a gas is called
sublimation, and is the cause of that
deterioration in foods known as “freezer
burn,” in which crystalline water evaporates
into the freezer’s cold, dry air. Freeze-drying
is a controlled version of the same process.
Many Food Molecules Can’t Change Phase
Most of the molecules that the cook works