Thickening a sauce with starch. Uncooked starch granules offer little obstruction to the flow of the surrounding liquid (left). As the sauce heats up and the temperature reaches the gelation range, the granules absorb water and swell, and the sauce consistency begins to thicken (center). As cooking continues and the temperature approaches the boil, the granules swell even more and leak starch chains into the liquid (right). It’s at this stage that the sauce reaches its maximum thickness.