Farmed mussels are higher quality than wild mussels because they are kept below the water even at low tide, allowing them to feed continuously so their meat content is higher. Another benefit is that they are also are kept above the bottom, reducing ingestion of the grit that often accompanies a wild mussel. The beard, the threads that attach the mussel to the rock or rope, should be removed before preparation. Mussels should be alive and tightly closed before being cooked. Open mussels should be discarded, as should any that do not open after they are cooked.
Individual mussels are about 2 1/2 to 3 inches high. The shell should be strong and should be closed.