WHY DO SHELLFISH TURN RED WHEN COOKED?
Shellfish include crustaceans like prawns, crayfish, crabs, and lobsters; molluscs like clams, scallops, oysters, and mussels; and even some echinoderms like sea urchins. However, not all shellfish turn red when cooked—this phenomenon is mainly observed in crustaceans such as shrimp and lobster.
These animals have a hard outer covering called an exoskeleton, which contains a pigment known as astaxanthin. Astaxanthin is a carotenoid, a class of organic pigments responsible for bright red, orange, and yellow hues in nature. In live crustaceans, this red pigment is tightly bound to specific proteins (like crustacyanin), forming a complex that gives the shell its bluish, greenish, or greyish colour.
When crustaceans are cooked, heat breaks down these protein-pigment complexes. The protein denatures and unfolds, releasing the free astaxanthin, which is naturally a vibrant red-orange. This chemical reaction explains the striking transformation in colour when these shellfish are boiled, steamed, or grilled.
Interestingly, astaxanthin is not just about colour—it also acts as a powerful antioxidant. In the wild, crustaceans obtain it from algae and plankton, which are rich in carotenoids. In aquaculture, it is sometimes supplemented in their diet to enhance their colouration.
Also, not all crustaceans follow this pattern. For example, a rare genetic mutation can lead to albino lobsters, which lack pigment entirely and do not change colour when cooked. Such lobsters are extremely rare—about one in 100 million!
So, the next time you see a bright red lobster on your plate, remember that it's the astaxanthin revealing its true colours once the protein camouflage is gone!
