The Food Lab: Better Home Cooking Through Science

Because microwave ovens allow so little energy to
be lost to the outside environment (unlike the way,
for example, a gas burner will heat up the room),
they are extremely efficient at heating water. But
there’s one thing to be aware of: it’s called
superheating, and it is as cool as it sounds. Heat up
water in a blemish-free container with minimal
disturbance, and because of a lack of nucleation
points (see here), it’s possible to heat it well beyond
its boiling point without it ever boiling. As soon as
some turbulence is introduced, though—a little
wobble from the turntable, for example—bubbles
burst forth, sending hot water all over the inside of
your microwave. This doesn’t happen on the
stovetop, since heating from the bottom of the pot
creates lots of convection currents (the movement
that occurs between relatively hot and cool regions
of liquid or gas). You can avoid this by sticking a
wooden spoon into your cup of water in the
microwave to provide nucleation sites.
It’s a lot like my lovely wife, who will quietly
suppress tiny annoyances until suddenly the slightest
disturbance sends her into an all-out rage.
Unfortunately, the wooden spoon method does not
work on her.