On food and cooking the science and lore of the kitchen ( PDFDrive ) 1127
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emulsion. Cream is an especially robust and
versatilebaseforemulsifiedsauces.
Foams: Thickening with BubblesAt first it
seemssurprisingthatafluidcanbethickened
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
moleculesandobstructthewater’sflowfrom
one place to another. The disadvantage of
foamsisthattheyarefragileandevanescent.
The force of gravity unceasingly drains fluid
fromthebubblewalls,andwhenthewallsget
just a few molecules thick, they break, the
bubbles pop, and the foam collapses. This
outcome can be delayed in a couple of ways.
The cook can thicken the fluid with truly
substantial particles or molecules (oil
droplets, egg proteins) to slow its drainage
from the bubble cell walls, or include
emulsifiers (egg-yolk lecithin) that stabilize
thebubblestructureitself.Ontheotherhand,
the very delicacy and evanescence of
unreinforced foams is a part of their appeal.
Such foams must be prepared at the last
minuteandsavoredastheydisappear.
Thickening a liquid with oil droplets and air
bubbles.Thesetinyspheresactmuchassolid
foodparticlesdo,interferingwiththeflowof
theliquidsurroundingthem.
Real Sauces: Multiple Thickeners The
sauces that cooks actually make are seldom
