what is crab mustard

Crab mustard is a yellow substance found inside a cooked crab, which is actually the crabs hepatopancreas. The hepatopancreas is an organ that filters impurities out of the crabs blood and is responsible for digestion. Crab mustard is not actually mustard, but it is called so because of its color. In Maryland and on the Delmarva Peninsula, the hepatopancreas of the blue crab is called the "muster" or "mustard". Crab mustard is considered a delicacy, particularly when eating steamed or boiled crabs.