On Food and Cooking

medium as water or oil, so air molecules
collide with the food less often, and take
longer to impart energy to it. Second, a cool
object in a hot oven develops a stagnant
“boundary layer” of air molecules and water
vapor that slows the collision rate even
further. (A convection fan speeds cooking by
circulating the air more rapidly and disrupting
the boundary layer.) Third, in a dry
atmosphere the food’s moisture evaporates
from the surface, and this evaporation absorbs
most of the incoming energy, only a fraction
of which gets to the center. So baking is much
less efficient than boiling or frying.
Of course, the oven’s thin medium is why
the oven is a good means for drying foods,
either partly — for example, to concentrate
the flavor of watery tomatoes — or almost
fully, to preserve and create a chewy or crisp
texture. And once the surface has dried and its
temperature rises close to the oven’s, then
carbohydrates and proteins can undergo the