By Harold McGee
Certain conditions can lead to fish flesh becoming unpleasantly soft. When fish flesh is depleted by migration or by spawning, their sparse muscle proteins bond to each other only very loosely, and the overall texture is soft and flabby. In extreme cases, such as “sloppy” cod or “jellied” sole, the muscle proteins are so tenuously bonded that the muscle seems almost liquefied. Some fish come out mushy when thawed after frozen storage, because freezing disrupts the cells’ compartments and liberates enzymes that then attack the muscle fibers. And enzyme activity during cooking can turn firm fish mushy in the pan.