The Food Lab: Better Home Cooking Through Science

physical and chemical changes are permanent. Once a
protein’s shape has been changed by adding energy to it,
you can’t change it back by subsequently removing that
energy. In other words, you can’t uncook a steak.
The distinction between heat and temperature can be one
of the most confusing things in the kitchen, but grasping the
concept is essential to helping you become a more rational
cook. Through experience, we know that temperature is an
odd measure. I mean, pretty much all of us have walked
around comfortably in shorts in 60-degree weather but have
felt the ridiculous chill of jumping into a 60-degree lake,
right? Why does one but not the other make us cold, even
though the temperature is the same? Let me try to explain.
Heat is energy. Third-grade physics tells us that
everything from the air around us to the metal on the sides
of an oven is composed of molecules: teeny-tiny things that
are rapidly vibrating or, in the case of liquids and gases,
rapidly bouncing around in a random manner. The more
energy is added to a particular system of molecules, the
more rapidly they vibrate or bounce, and the more quickly
they transfer this movement to anything they are touching—
whether it’s the vibrating molecules in a metal pan
transferring energy to a juicy rib-eye steak sizzling away or
the bouncing molecules of air inside an oven transferring
energy to the crusty loaf of bread that’s baking.
Heat can be transferred from one system to another,
usually from the more energetic (hotter) system to the less
energetic (cooler). So when you place a steak in a hot pan to
cook it, what you are really doing is transferring energy
from the pan-burner system to the steak system. Some of