Is it OK if mussels are open before cooking?
Even though some mussels might appear to be badly damaged, it’s always worth cooking them as they could still open. If they do open, this means they’re still safe to eat (and just as tasty) as their better looking chums!
How open is too open for mussels?
Unless they have been shucked and frozen, mussels should be alive when you buy and cook them. If the shell is tightly closed, it is still alive. If the shell is slightly open, it should close promptly when tapped. If the shell is open and does not close when tapped, throw it out.