Much like aging a great piece of beef, aging fish helps deepen the flavor and improve the texture of the meat. As fish ages, the amino acid chains break down, which creates the rich umami flavor that makes these sea creatures so appealing. Enzymes located in the muscle cells of fish break down proteins, fats, and glycogen into sugars and various amino and fatty acids, developing flavors ranging from umami to sweetness to subtle bitterness in the process. With the reduced moisture in the careful preservation process, these flavors shine. Enzymes also help break down connective tissue, leaving fish with more tender, palatable profiles.

Like most living things, fish go through rigor mortis after death. When the cells run out of energy, they basically stiffen up. But as the fish ages and enzymes start breaking down the muscle fibers, the fish becomes more tender. Any experienced tuna fisherman will tell you that while the sight of cutting up a tuna on the boat as soon as it’s caught may look very tempting, the tuna will be tough, rubbery, and taste watery. Only after the fish has been in the fridge for a few days will it become more tender and flavorful.