Scrub the mussels with a stiff brush, removing the beards and any sand or grit.
Soak in cold water for 1 hour and drain before cooking.
Place the sake, garlic, ginger, coriander, and black pepper in a very large, shallow saucepan.
Bring to a boil over high heat and cook for 5 minutes, stirring frequently.
Add the mussels and return to a boil.
Reduce the heat to moderate, cover, and cook for 4 to 6 minutes or until most of the mussels have opened.
Remove the opened mussels and place in a serving bowl.
Cover and cook the remaining mussels for 2 minutes.
Add the opened mussels to the serving bowl, discarding any unopened mussels.
Spoon the cooking liquid over the mussels, and serve at once.