Secret Colors in Lobsters and Shrimp

Q: We peeled and cleaned dark blue-gray shrimp. When we steamed them, they turned bright orange. What chemical reaction causes this?
Matt Thomas, 9th grade, Peralta, NM

A: I pick up the phone, and dial UNM.

"Biology, University of New Mexico", a young lady answers.

I ask to speak with an authority on shrimp and lobsters.

"A marine or aquatic biologist...hmm," she considers a moment, and exclaims, "you're pretty far from either coast to get an expert!"

The Internet to the rescue. In a flash I contact two chemists from the west coast: Anne Gardiner and Sue Wilson, who teach a course on cooking chemistry at the University of British Columbia.

Gardiner and Wilson explain that lobster, shrimp, and crab shells have two colors: blackish and orange-pink. Crustaceans look blackish while alive because the orange-pink color exists but is hidden.

The chemists get down to the basics of molecular structure to elucidate. The blackish color is due to protein chains. The orange-pink color is a pigment, similar to the one in carrots. The protein chains hide the orange-pink molecules by wrapping around and containing them. Therefore the shell looks blackish.

What happens if you steam the shrimp or lobster? The protein chains undergo a chemical change when heated: they uncoil and release the orange-pink molecules. The orange color is no longer hidden, and the shell turns orangish-pink.

Surfing the Internet to the east coast, I encounter a professor of bio-systems and engineering at the University of Maine with a poetic flair.

"It's a lot like [autumn] leaves turning color," says Bob Bayer. The red was there but hiding.

The Gulf of Maine Aquarium says live lobsters are usually greenish-black on top and orange below, with accents of blue on the claw joints. This rainbow of colors results from only three pigments: red, blue, and yellow. What happens in the rare event pigments are missing at birth?

"A lobster may be red, blue, albino, or calico (dark with yellow spots)," they report.

Moreover, albinos don't turn red when cooked but all other lobsters do.

I surf on until I find this gem from Rebecca Jollensten, a web designer and lobster lover. Why do lobsters turn red?

"Embarrassment. Pure and simple."

Further Reading

"All about lobsters", Gulf of Maine Aquarium

Cooked shrimp, the Science of Cooking, SiamCanadian.com