The first step in making miso salmon is to prepare the marinade. In a small saucepan, combine the sake, mirin, soy sauce, white sugar, miso paste, and grated ginger. Stir the mixture until the sugar has dissolved and the miso paste has fully incorporated into the liquid.

Once the marinade is ready, pour it over the salmon fillets, making sure each fillet is evenly coated. Cover the salmon with plastic wrap and refrigerate for at least 30 minutes to allow the flavors to fully develop.

While the salmon is marinating, preheat your grill to medium-high heat. Make sure to clean the grates thoroughly to prevent the salmon from sticking.

Once the grill is hot, remove the salmon from the marinade and place it on the grill, skin-side down. Grill the salmon for about 4-5 minutes on each side or until it is fully cooked through.

The internal temperature of the salmon should reach 145°F. Keep a close eye on the salmon while it's grilling to prevent it from overcooking and becoming dry.