emulsion. Cream is an especially robust and
versatile base for emulsified sauces.
Foams: Thickening with Bubbles At first it
seems surprising that a fluid can be thickened
by adding air to it. Air is the opposite of
substantial! Yet think of the foams on an
espresso coffee or a glass of beer: they all
have enough body to hold their shape when
scooped with a spoon. Similarly, a pancake
batter gets noticeably thicker if you stir the
chemical leavening in last. In a fluid, air
bubbles have much the same effect as solid
particles: they interrupt the mass of water
molecules and obstruct the water’s flow from
one place to another. The disadvantage of
foams is that they are fragile and evanescent.
The force of gravity unceasingly drains fluid
from the bubble walls, and when the walls get
just a few molecules thick, they break, the
bubbles pop, and the foam collapses. This
outcome can be delayed in a couple of ways.