Like Amanda, I hardly see much in the way of beards on mussels that I buy. Before these beauties were widely available and we mostly harvested them ourselves, we were warned to cut the byssal threads rather than pull. Or if we were pulling, cook them immediately. Mussels aren't the most hardy of kitchen bivalves, and it's better to deal with a little beard than have a bunch of mussels go bad.

The mussels I buy are from the West Coast and I've never had trouble just yanking off the beard. But if a little is still inside the shell, so what? It's hardly worth detailing each cooked mussel

Sorry not to be more helpful, but pulling the beard off firmly, before cooking, is the only method I know of. What kind of mussels are you buying? Seems like the most common ones you find -- the PEI mussels -- barely have any beards at all.