The Food Lab: Better Home Cooking Through Science

Reason 1
To test this, I brought three pots of water to a boil: one with
6 quarts of water, one with 3 quarts, and one with a mere
quart and a half. After the water in each pot came to a boil, I
added the pasta and waited for it to return to a boil. The
three pots did so within seconds of each other. In fact, the
pot with 3 quarts actually came back to a boil slightly faster
than the one with 6 quarts—the exact opposite of what is
supposed to happen. What gives?
To solve this mystery, we have to think about what’s
going on inside a pot of boiling water, what its energy
inputs and outputs are. Imagine we have two pots of water
on identical burners. One pot holds 2 gallons of boiling
water and the other holds 2 quarts. The inputs are simple:
the burner underneath each one is supplying a constant
energy source. As long as the burners are set at high, the
amount of energy they transfer to the pot-water system is
consistent. What about energy loss? Well, that’s going on
too. First, there’s energy being lost to the outside
environment in the form of heat from the sides of the pot
and the surface of the water. This amount of energy loss is
proportional to the surface area of the pot-water system as
well as its temperature. Since the temperature is staying at a
constant 212°F, and the pots are (presumably) not changing
size, that too is a constant. The other factor that contributes
to energy loss is something called the heat of vaporization—
that’s the energy it takes to convert water into steam. Both
pots of water are boiling, and the difference between
energy-in and energy-out is compensated for by the energy
used to boil that water.