retrogradation

noun

1. Motion in a retrograde manner

2. Decline, degradation

3. (chemistry) A reaction that takes place in gelatinized starch when the amylose and amylopectin chains realign themselves, largely responsible for bread becoming stale.

- The major reason that bread stales is not moisture loss, but rather a process called retrogradation, in which the starch molecules in the bread crystallize.