Why Do Crawfish Turn Red When You Boil Them?

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Food photographers often pose brilliantly red lobsters, crabs or crawfish in outdoor settings, where their color shows to advantage against a pier or dark seaside rock. It makes for an effective composition visually, but it's amusingly silly to anyone who knows seafood. Crawfish and their crustacean kin only gain their signature red color when cooked, one of the culinary world's most dramatic transformations.

A Quick Family Snapshot

  • Crawfish -- also known as crayfish, crawdads, mudbugs or just "bugs" -- are part of the larger family of crustaceans, along with crabs, shrimp and lobsters. Crustaceans have a distinctively sweet and nutty flavor, thanks to their unusually high levels of sugars and "free" amino acids, which aren't bound up in whole protein molecules. They're able to develop richly savory flavors even in low-temperature cooking, which animal meats can only match through high-temperature browning. Shrimp, crawfish, langoustines and lobsters are all very similar in their anatomy, sharing a muscular tail and -- in some species -- big, meaty claws. American crawfish are smaller than lobsters, but their kin elsewhere can be just as large.

It's a Diet Thing

  • In the aquatic environment, the bottom level of the food chain is occupied by plankton, microscopic plants and animals. Many varieties of plankton contain pigments similar to those found in terrestrial vegetables, including red and orange compounds such as astaxanthin and beta carotene. As the plankton are eaten by insects and tiny shrimp, those compounds accumulate in their tissues. As those in turn are eaten by larger shrimp and then crawfish, the color compounds reach significant concentrations. Crawfish and their kin rely on camouflage and concealment for their survival, so their bodies conceal the vivid pigments by binding them with a protective covering of protein molecules.

The Red Coats are Coming

  • By the time they reach maturity, crawfish shells are rich in those color-bearing pigments. Cooking doesn't actually change the color of the tasty crustaceans' shells; it simply reveals a color that's already present but hidden. When the crawfish are poured into boiling water, the protein molecules in their shells quickly unwind -- or "denature" -- under the impact of the water's heat. As they do so, the bold and vivid red hue underneath becomes plainly visible.

Dinner and a Show

  • That vivid color adds greatly to the visual appeal of the crawfish, which is one reason crawfish are seldom shelled before cooking. Another is the well-attested fact that the shells contain a great deal of flavor. When the crustaceans are cooked, water- and fat-soluble flavors infuse into their flesh from the shells. The shells can also be saved, roasted and crushed, then simmered in water or butter to extract additional flavor. The resulting broth serves as a base for soups and rice dishes. Once strained, the crawfish-flavored butter makes a fine base for rice dishes or sauces.

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References

  • On Food and Cooking: The Science and Lore of the Kitchen; Harold McGee
  • On Cooking: A Textbook of Culinary Fundamentals; Sarah Labensky et al.
  • Nordic Recipe Archive: Crayfish
  • Photo Credit Jupiterimages/liquidlibrary/Getty Images
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