A cracked open crab with hepatopancreas inside.


No, The Yellow Stuff That Oozes Out Of Crab Isn't Actually Mustard
Once you breach a crab’s exoskeletal barrier, you’ll find chunks of crab meat along with the hepatopancreas, which many people incorrectly confuse with mustard.
The hepatopancreas is a digestive organ that filters blood circulating in the crab's body and releases digestive enzymes that can break down the toxins caught by the filter.
Apart from mustard, the hepatopancreas is often known by various nicknames. There are those who call it crab fat and those who prefer the term tomalley.
The hepatopancreas is quite delicious and is used as an ingredient in many recipes, such as chef Cat Cora’s Dungeness crab "buon Natale" with tomalley sauce.
Swan Oyster Depot, a San Francisco seafood restaurant loved by the late chef Anthony Bourdain, served up a dish of Dungeness tomalley that was said to be a favorite of his.
Some cooks often discard the tomalley instead of eating it because its filtering function indicates a high dose of dioxin and toxic metals.
The Agency for Toxic Substances and Disease Registry advises eating no more than two crabs per day, while New York’s health department recommends discarding the substance entirely.