Quinoa becomes sticky when refrigerated because the starch molecules retrogradate, meaning they re-associate and crystallize, trapping water and creating a sticky texture. This is exacerbated by excess moisture present during cooking.
When quinoa is cooked, the starch granules absorb water and swell, a process called gelatinization. Upon cooling, especially in the refrigerator, these starch molecules undergo retrogradation. Retrogradation is the process where the starch molecules realign themselves and form a more ordered structure. This process forces water out of the starch granules, but the water remains trapped within the quinoa, leading to a sticky and sometimes gummy texture. The amount of water used during the initial cooking significantly impacts the stickiness. If too much water is used, more starch will be released, and more water will be available to be trapped during retrogradation. The type of quinoa can also play a role, as some varieties naturally contain more starch than others. Furthermore, the rate of cooling affects the degree of retrogradation; rapid cooling in the refrigerator promotes faster retrogradation and thus, increased stickiness.
To minimize stickiness, rinse quinoa thoroughly before cooking to remove excess starch, use a precise water-to-quinoa ratio (typically 2:1), and fluff the quinoa with a fork immediately after cooking to release steam.