Why Leftovers Taste So Good

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Refrigeration allows for all of the various flavors in the dish to migrate into the cooling protein and starches. When stewed meat cools down, the gelatinous material from the collagen and tendons etc. that has melted during cooking begins to gel in and around the chunks of meat. As this happens, the various flavor compounds get trapped in the gel. With ground meat this is amplified even more because there's even more surface area for the gel and trapped flavor compounds to disperse over. The same goes for starches. When you cook a starch it gelatinizes. This means that it undergoes a distinct crystallography change - it will no longer have a crystalline structure but will be amorphous or fluid, and that's when it's digestible. As it cools down, the starch goes through a process called retrogradation and the molecules begin to to rearrange and realign themselves into a crystalline structure again. As it does, this flavor compounds from the surrounding sauce are trapped inside the structure.