Most of the seafood that goes into your sushi is actually aged—intentionally and not.
It’s a romantic idea: tuna bought fresh at the Tsukiji fish market, airlifted to your city within 16 hours, and cut into sashimi to stuff in your gullet within a day. Sushi and sashimi are all about good ingredients, and fresh fish is the best fish, right? Not necessarily. For one, unless you live within an hour’s drive of fishing waters, your fish has likely been frozen, even if it’s defrosted and sold as ‘fresh.’
Deep-freezing fish right after gutting kills harmful parasites and is the surest way to preserve the meat’s texture and flavor until it arrives at your market. From there, many sushi chefs will intentionally age the fish for several days to a couple weeks before slicing it for sushi. Why the wait? As any Law and Order fan knows, corpses enter a state called rigor mortis a few hours after death, in which the joints and muscles stiffen up, and they remain that way for up to several days.
Aging the fish past rigor mortis in the refrigerator gives those muscles time to loosen up again, which means a more tender bite of fish, and as some moisture evaporates from the muscle during this aging, you get a more flavorful bite as well.