On Food and Cooking

Like emulsions, foams are a dispersion of one
fluid in another. In the case of foams, the fluid
is not a liquid, but a gas, and the dispersed
particles are not droplets, but bubbles. Still,
the bubbles do the same thing that droplets do
in a sauce: they get in the way of water
molecules in the sauce, prevent them from
flowing easily, and thus give the sauce as a
whole a thicker body. At the same time, they
provide two unique characteristics: a large
surface area in contact with air that can
enhance the release of aromas to the nose; and
a light insubstantiality and evanescence that
offers a refreshing contrast to the texture of
nearly any food they accompany.
There’s one classic foam sauce, the
sabayon, which is made by cooking and
whipping egg yolks at the same time to form a
stable mass of bubbles. And both whipped
cream and whipped egg whites can be folded
with their bubbles into any water-based sauce.
But cooks nowadays make foams from all