The Food Lab: Better Home Cooking Through Science

In their raw state, starch molecules are bundled
tightly together into granules. In order to activate
their thickening power, these granules need to
absorb water. As water gets heated, these tiny
granules gradually swell up like miniature water
balloons until finally, at around 130°F, they burst,
spreading individual starch molecules throughout the
liquid and thickening it. The starches continue to
absorb water and swell further as the liquid is heated
toward its boiling point. When adding starch to a
liquid, it’s essential to heat the sauce to serving
temperature in order to gauge its thickening power.
There’s one thing to remember: if you add dry
starch quickly to hot liquids, it rapidly forms into
clumps. The starches on the exterior of these clumps
will swell and jell, preventing liquid from reaching