America's Test Kitchen LogoCook's Country LogoCook's Illustrated Logo

What's That Green Stuff in Lobster (And Can I Eat It)?

Seafood lovers beware. This one-time delicacy comes with big caveats.

hero image

Many seafood lovers wonder about the soft, green substance that’s found inside cooked lobsters and other crustaceans. Known as the tomalley, the paste was once considered a delicacy because of its creamy texture and rich, concentrated flavor. Currently, it is not advisable to eat tomalley, but the situation changes from time to time (and from region to region), so this may not be a permanent ban.

What Is Lobster (or Crab) Tomalley?

The green substance in the body cavity of a cooked American or Maine lobster (Homarus americanus) is a digestive gland, sort of like a liver and a pancreas combined. It’s known to marine biologists as the hepatopancreas and to lobster fans as the tomalley. The tomalley is also found in rock, or spiny, lobster (Panulirus argus) and all species of crab. 

Is It Safe to Eat Tomalley?

At the present time—no. According to the Maine Center for Disease Control and Prevention, American lobster tomalley is harmful to ingest because it can “accumulate contaminants found in the environment.” These include mercury, PCBs (polychlorinated biphenyls), and dioxins that settle into the ocean from the air and via rivers. At high levels, they have been linked to serious health issues. 

There have also been warnings from the California Department of Fish and Wildlife not to consume the tomalley of rock, or spiny, lobsters due to “unhealthy” levels of domoic acid, a neurotoxin. Among other symptoms, ingestion of sufficient amounts of domoic acid can lead to amnesic shellfish poisoning, so-named because it can permanently damage short-term memory. 

Crab tomalley (sometimes called crab mustard or crab fat) is also of concern. The New York State Department of Health has advised consumers to remove and discard the tomalley of blue crab since it’s where PCBs, dioxin, and metals concentrate in the crustacean. Additionally, the California Department of Public Health found elevated levels of domoic acid in the tomalley of Dungeness crabs. Domoic acid can also leach into cooking liquids, so it should be discarded after steaming or boiling.

The good news is that it’s still OK to eat the meat of lobster and crab: Studies have shown that even when high levels of toxins are present in the tomalley of a crustacean, the flesh is typically unaffected.

This is a members' feature.