On Food and Cooking

(p. 583).
Swelling and Gelation What makes starch so
useful is its behavior in hot water. Mix some
flour or cornstarch into cold water, and
nothing much happens. The starch granules
slowly absorb a limited amount of water,
about 30% of their own weight, and they
simply sink to the bottom of the pot and sit
there. But when the water gets hot enough, the
energy of its molecules is sufficient to disrupt
the weaker regions of the granule. The
granules then absorb more water and swell up,
thereby putting greater and greater stress on
the more organized, stronger granule regions.
Within a certain range of temperatures
characteristic of each starch source but
usually beginning around 120–140ºF/50–60ºC,
the granules suddenly lose their organized
structure, absorb a great deal of water, and
become amorphous networks of starch and
water intermingled. This temperature is called
the gelation range, because the granules