[1] When native starch is heated and dissolved in water, the crystalline structure of amylose and amylopectin molecules is lost and they hydrate to form a viscous solution.
If the viscous solution is cooled or left at lower temperature for a long enough period, the linear molecules, amylose, and linear parts of amylopectin molecules retrograde and rearrange themselves again to a more crystalline structure.
The linear chains place themselves parallel and form hydrogen bridges.
The temperature range between cooking starch and storing in room temperature is optimum for amylose crystallization, and therefore amylose crystallization is responsible for the development of the initial hardness of the starch gel.
Additives such as fat, glucose, sodium nitrate and emulsifier can reduce retrogradation of starch.