retrogradation

Noun

 * 1) Motion in a retrograde manner.
 * 2) Decline, degradation.
 * 3)  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.