The Food Lab: Better Home Cooking Through Science

So: energy-in, energy-out. With me so far?
Now, what happens when we add some room-temperature
pasta to the pots? The temperature of the water immediately
drops. How much it drops is inversely proportional to its
total volume. The more water you have to begin with, the
smaller the temperature change. A pound of pasta added to
the 2-gallon pot will cause it to drop by only a degree or
two, while a pound of pasta added to the 2-quart pot will
cause a temperature drop four times as great (since a gallon
is four times as big as a quart).
Aha! you must be thinking. So the reasoning is correct.
Lower volume means a bigger drop in temperature, which
means a longer time to get back to a boil.
On the face of it, it seems logical, but the problem is that
it takes more energy to raise the temperature of 2 gallons of
water than it does to raise the temperature of 2 quarts. How
much more? Exactly four times more, in fact. And since our
small pot dropped in temperature precisely four times as
much as our large pot, it means that both pots will come
back up to their boiling point in the same amount of time.
To make it simpler, think about this: if you heated your
pasta to 212°F before dropping it into the pot of boiling
water, the water would not cool at all and thus never lose a
boil, no matter what volume of water you started with. So,
the only energy we really need to add to the system—
regardless of the size of the pot—is the energy it takes to
bring the pound of pasta up to 212°F. And that, my friends,
is a constant.
So it’s “pasta la vista” to Reason 1.