Once you put a crab or a prawn in a pot of boiling water or on a grill, heat destroys the crustacyanin protein. Then, the orange-ey astaxanthin is released, turning the shell of the crustaceans bright red.

Why do crabs turn red when dead?

After it's cooked, it all turns into a delicious bright red. ... We mentioned earlier that the crab's shell contains a red pigment called astaxanthin that naturally appears red. This same organic pigment, or carotenoid, turns carrots orange or salmon pink.

Why are crabs different colors?

The dramatic color change during cooking has to do with the way certain biochemicals inside the shellfish react to heat. Lobsters and crabs have a pigment called astaxanthin in their shells. ... The astaxanthin-crustacyanin complex then winds up giving off a blue-green color.