MUNDANE MYSTERIES: Why Do Lobsters Turn Red When You Cook Them?

If you’ve ever taken on the challenge of steaming a lobster, you know they end up a bright red color that’s very different from the original color they start out with. Why is that?

That bright, fire-engine red color is merely the result of a simple chemical reaction. Lobsters’ usual greenish-blue hue works well for them in life, as it camouflages them from predators like cod, haddock, and other large fish stalking the ocean floor. A lobster’s original color is due to a combination of two different molecules: a protein lobsters already have, called crustacyanin, and a bright red carotenoid lobsters absorb by eating things that contain it, called astaxanthin. When crustacyanin binds with astaxanthin, it twists the molecule into a different shape, which changes how it reflects light. So instead of red, live lobsters are blue.

But, when you boil a lobster, the heat causes the crustacyanin molecules to contort into new shapes & forces them to release the astaxanthin molecules, which rebound to their original shape & red color. The same thing happens with shrimp, which go from gray to pink when you cook them. Fun fact: this process is also why flamingos are pink. When they eat the raw, almost colorless shrimp, the crustacyanin in the shrimp ends up releasing its hold on the astaxanthin during the flamingos’ digestion process…just like it would if you were to heat it up in a pot or skillet.

So, now you know why your lobster (and shrimp) changes color when you cook it. The only mystery left to solve is: which seafood restaurant are we gonna eat at tonight?

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