INCORPORATING STARCHES

Have you ever tried adding flour or cornstarch

directly to a hot soup in an attempt to thicken it, only
to find that the starch clumps up into frustratingly
impossible-to-destroy little balls? Here’s the
problem, and it has to do with the nature of the
interaction between starch—a complex
carbohydrate found in all sorts of plant matter,
including flour—and water. Remember those little
dinosaur-shaped sponges you’d get as a kid, which
you’d drop into water, then wait for them to grow?
That’s exactly what starch molecules are like. When
dry, they are tiny and shriveled. They can flow
freely past each other. But expose them to water,
and they start growing, getting bigger and bigger,
until they eventually rub up against each other and
bind, creating a water-resistant barrier. Are you
starting to get the picture?
When a spoonful of flour or cornstarch lands on
the surface of a pot of water or milk, the first parts
to get wet are the starches on the outside of the
granules, which rapidly expand, forming a
waterproof seal. As you stir and submerge the
clumps, a seal ends up forming around the entire
clump, keeping the interior from getting wet.
So, how do you solve this problem? Two ways.