Mussels are not hard to clean. First toss any that have broken shells or shells that won’t close when tapped. Scrub the remaining mussels with a stiff brush under cold, running water. Finally, pull off the dark fibrous threads, also known as the “beard.”
Mussels should be alive and fresh when you buy them and when you cook them. Look for mussels that have tightly closed shells or those that snap shut when you tap them.