It's a Diet Thing

• The well-worn adage that "you are what you eat" is at the root of cooked crab's lurid color. The culprits in this case are a group of food-based pigments, such as astaxanthin and beta carotene, which produce rich hues of red and orange. They're present in the microscopic plants, called plankton, that form the lowest level of the underwater food chain. As they're eaten by tiny shrimp and other creatures, then in turn devoured by crabs and larger predators, those pigments become ever more concentrated. Humans sometimes experience a similar effect from eating too many carrots or consuming "tanning" pills high in beta carotene. The excess pigment turns your skin an oddly orange color, which simulates a suntan.

Keeping it Under Cover

• In a human, consuming enough beta carotene to turn orange can inspire some rough humor, but it isn't directly life-threatening. That's not the case in the crabs' world, where blending into your environment is a survival skill rather than a social skill. Because bright-red crabs would have a poor life expectancy, their bodies conceal those bright red pigments by wrapping them in a thin layer of proteins. This molecular-level disguise helps crabs remain unobtrusively brown or green, masking them from the scrutiny of predator and prey.

Brighten Up

• When the crabs are harvested and their legs cooked, everything changes. Protein molecules react to heat by contracting and becoming firm, like a thin piece of bacon in a hot skillet. Within the crab's shell, the same thing happens on a smaller scale. The shrinking proteins are no longer able to mask the brightly colored pigments stored in the shell, shrinking away and revealing the appetizing hues beneath. This takes just a few moments in boiling water, or slightly longer in a steamer.

Not a Compromise

• Some food writers and television shows tend to romanticize their ingredients, disdaining anything frozen and insisting on freshness above all. In the real world, those two attitudes are often contradictory. Fresh crabs are among the most perishable of seafood, quickly dying once they're pulled from the water and deteriorating almost as quickly. Commercial crab harvesters typically cook and freeze the legs immediately, either right on the boat or as soon as they're landed. This captures their peak of freshness and flavor, preserving it through the long miles that stand between the boat and your table.