Why does idly stop getting fluffier when cooked?

Idly stops getting fluffier when cooked due to a few key factors. As the fermentation process produces carbon dioxide, it creates air pockets that help the batter rise. However, once the cooking temperature is reached, the proteins in the batter coagulate and the starch granules gelatinize, setting the structure. If the batter is overcooked or the fermentation is inadequate, it can result in denser idlies that lack the desired fluffiness.