Shrimp flavor declines in just a few days on ice due to the slow loss of amino acids and other tasty small molecules. But thanks to their protective cuticle, shrimp can remain edible for as much as 14 days. Shrimpers often treat them with a bleaching solution of bisulfite to prevent discoloration, and like scallops, with a sodium polyphosphate solution to keep them moist; these practices can cause off-flavors.
The mainly muscular “tail” of the shrimp amounts to about two-thirds of its body weight, so producers often separate it from the flavorful “head” and its midgut enzymes, which can accelerate spoilage. The dark “vein” along the outside curve of the abdomen is the end of the digestive tube, and can be gritty with the sand from which the animals glean bacteria and debris; it’s easily pulled away from the surrounding muscle. Though peeled, cooked shrimp are widely available and convenient, serious shrimp lovers seek out fresh whole shrimp and cook them in the shell, rapidly and briefly.