What it actually is
Cooking disorders the starch: granules swell, crystalline regions melt and the chains uncoil into a hydrated gel. That state is not where the starch wants to be. Over hours and days the chains find each other again and rebuild ordered regions, expelling water as they do. Amylose, being linear, does this in hours. Amylopectin, being branched, takes days.
Why it matters
It is staling in bread, weeping in a chilled sauce, graininess in a ready meal, and firmness in anything held cold. It is also, in exactly one category, the objective: a starch noodle has no gluten, so the retrograded amylose network is the entire structure of the product.
What changes it
Amylose content first, then temperature, since retrogradation is fastest just above freezing and effectively stops when deep frozen. Chemical stabilisation of the starch prevents it; choosing a waxy starch avoids it; choosing a high amylose starch invites it deliberately.
