Mussels should be kept cold in the refrigerator. It's best to store mussels in a bowl in the refrigerator covered with a wet paper towel to maintain humidity. Do not store in water, fresh water will kill them. Before preparation, each mussel should be checked by tapping the shell lightly. Mussels whose shells don't close in a minute or two are likely to be dead and should be discarded.
Many recipes suggest soaking mussels in water in which cornmeal has been added.
This technique was suggested to help the mussel purge sand from its body, and the cornmeal was added to provide food to encourage the mussel to pump water through it's system. While in principle this technique could help to remove some sand or grit, it is generally considered to be unnecessary, impractical, and of marginal benefit for most consumers. The delicious briny aroma that mussels release and the broth their juices create as they cook adds to their wonderful versatility. This broth can be used as the base for an almost infinite variety of soups, seafood stews, and sauces. Mussels can also be lightly broiled on the half shell, deep-fried, stuffed tossed into salads, or even grilled.