Why do shellfish turn red when cooked?

I used to think the reason the lobster on my plate was red, while the lobster swimming in the ocean was grey/brown, was just due to the species of the animal. Umm, no….it’s actually food science! 

Astaxanthins are red pigments that crustaceans accumulate in their body from the food they eat, just like salmon and flamingos. This pigment comes from the plankton and algae that they feed on.

So why can’t we see red lobsters in the ocean? Protein! Shellfish such as lobster have crustacyanin proteins in their bodies that bind to astaxanthins and mask the color. This protein is a blue-ish color that explains why there is such a difference in appearance.

Why?? If shellfish didn’t have this protein, they would be much easier for predators to spot.


As the lobster is cooked, heat causes the proteins to denature. This means the proteins unravel and unbind from the astaxanthin. Because the protein is no longer wrapped around the pigment, the beautiful red color is now visible!


Farrimond, S. 2017. The science of cooking. DK Publishing. New York, New York. 

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