Best to store mussels in the bottom of your refrigerator. Covered with a damp cloth or wrapped in wet newspaper.
They are best cooked the same day, but will keep, refrigerated at 40 degrees, for 5-8 days. The double checking as to whether they were alive comes after they are steamed: If they fail to open, throw them out.
Allow the frozen mussels to thaw overnight in the refrigerator in a container with a sealed lid. Run warm water over a container of frozen mussels if time is of the essence, however gently thawing them out in the refrigerator yields more tender results.
Heat frozen mussel meat in a sauce pan once fully thawed, then eat them as is or add to other recipes, such as spaghetti sauce or soup.
Steam frozen mussels still in the shell for three or four minutes in a covered saucepan over medium-high heat with butter, garlic, and a tablespoon of extra virgin olive oil, then reduce the heat and simmer for a few minutes longer. The shells should open; discard any that remain closed.
NOTE: Frozen mussels may open in transit…they are perfectly safe to thaw, prepare, and eat.