retrogradation

"Cooking a potato is a two-stage process. The starch swells and gelatinizes within the cells when the potato reaches 160 degrees; then, nearer to the boiling point, the pectic cement between the cells degrades, and the potato can be safely matched. Cooling the potato slices after the starch has gelled causes a process called retrogradation to take place; the starch molecules bond to one another and lose much of their ability to dissolve again in water or milk, even if you later rupture the cells."

It will crisp it up, but, fact fans, that heat will also briefly reverse retrogradation – the staling process of starches reverting to their crystalline form.

The retrogradation of wheat starch in bread is responsible for staling.

Retrogradation is referred to as “staling” in the baking industry.

If you want to know the science behind it, it’s got to do with the same retrogradation of starch that stales bread and firms rice for stir-frying.