Crab boil usually refers to a spice mixture that is used to flavor the water in which crabs or other shellfish are boiled. Homemade crab boil recipes call for abundant amounts of hot sauce, cayenne pepper, salt, bay leaf, lemon, and garlic. Mustard seeds, coriander seeds, and allspice are popular extra options. Many people will start with a commercial crab boil product and then supplement it with extra pepper. The leading commercial product is Zatarain's which comes in two forms.