On Food and Cooking

divide the liquid into many small, local
masses: and by dividing, they organize and
collect it and give it a kind of coherence that
it lacked beforehand. Some thickening agents
also literally bind water molecules to
themselves and so take them out of circulation
altogether, and this too has the effect of
reducing the fluidity of the continuous phase.
In addition to giving watery fluids a
thicker consistency, the substances in the
dispersed phase can give them textures of
various kinds. Solid particles may make them
grainy or smooth, depending on the particle
size; oil droplets make them seem creamy;
dispersed molecules with a tendency to adhere
to each other may make them seem sticky or
slimy; air bubbles make them seem light and
evanescent.
There are four common ways of thickening
watery food juices. Each produces a different
kind of physical system, and lends different
qualities to the finished sauce.