Food Facts, Food information, and Tips!



The world of cooking has many legends, rumors and myths. We are trying to gather all the facts and present them to you.



Tell Us a Fact or Myth/Rumor



Why does a crab's shell turn red when cooked?



The red pigment is the most stable component of the coloring in a crab shell. The greens, blues, and browns which darken the shell in a live crab are destroyed by cooking. The red pigment common to all decapod (shrimp, prawn, crab, lobster) exoskeletons (shells) is astaxanthin, a carotenoid (like Beta-carotene, the pigment that makes fruits red-orange) found in many organisms from bacteria to birds. Astaxanthin was first identified in the exoskeletons of crayfish, Astacidea, hence its name. In crabs, as in many decapods, astaxanthin is not a free pigment, but is complexed with a protein called Alpha-crustacyanin, which alters the resonance of astaxanthin such that the complex acts as a blue-green pigment. As mentioned above, astaxanthin is heat stable, while the Alpha-crustacyanin protein is not, so boiling the crab shell denatures the blue-green Alpha-crustacyanin releasing the red-orange astaxanthin.