Live, fresh mussels are generally available year-round. Buy mussels with tightly closed shells or those that snap shut when tapped. Do not purchase mussels with broken shells. Also, avoid buying mussels that are heavy, for they are usually full of sand, or light in weight, as they are usually dead. Smaller mussels will be more tender than larger ones. Mussels should be used within a day or two of purchase.