On Food and Cooking

Interpreting the Foam’s Appearance There
are various ways to judge when the foam is at
its optimum, from seeing whether the foam
will support the weight of a coin or an egg, to
seeing how it supports itself, in soft mounds
or sharply defined peaks, to seeing whether it
clings to the bowl or slips along its surface,
whether its surface looks glossy or dry. All
these tests tell us how crowded the air bubbles
are, and how much lubrication they have
between them in the way of liquid from the
egg white. And different dishes will define an
optimum foam differently. The lightening
power of an egg foam depends not just on the
foam’s volume, but also on how easily it can
be mixed with other ingredients, and how well
it can accommodate bubble expansion in the
oven. Soufflés and cakes require the
lubrication and expansion tolerance of a
somewhat underbeaten foam, while in
meringues and related pastries volume is less
important than shape-holding stiffness.