By Harold McGee
Slow and gentle heating has an important place in meat cooking, and some fish—Atlantic salmon, for example—can develop an almost custard-like texture if heated gently to 120°F /50°C. In fish cooking, however, slow cooking can sometimes produce an unpleasant, mushy texture. This is caused by protein-digesting enzymes in the muscle cells of active fish and shellfish that help convert muscle mass into energy. Some of these enzymes become increasingly active as the temperature rises during cooking, until they’re inactivated at 130–140°F/55–60°C. Mush-prone fish (see box) are best either cooked quickly to an enzyme-killing but somewhat drying 160°F/70°C, or else cooked to a lower temperature and served immediately.