To extract the blackberry juice, force the berries through a mesh strainer. Discard the solids. 11 ounces of blackberries should yield about 3/4 cup of juice, so you may have a little extra (perfect forBlackberry Ginger Martinis).
Combine the blackberry juice, balsamic vinegar and light brown sugar in a medium skillet. Bring to a simmer and then reduce the heat to medium, stirring frequently until the volume has reduced down to 1/4 cup (about 15 minutes). This not only thickens the sauce, but also brings out the sweetness of the balsamic vinegar.
Transfer the blackberry balsamic reduction to a double boiler or stainless steel bowl to keep warm over a hot water bath while you grill the fish.
Prepare the grill fordirect grillingover a medium fire (about 400°F) and with a cooler orindirect zonethat may be needed for perfectly cooking the fish.
Rinse the fish and pat dry with paper towels. You can cook the fish as one piece and divide it later (which makes it a little easier to grill), or you can slice the fish into four pieces prior to grilling. Lightly brush the fish with olive oil on all sides but the skin and then sprinkle with salt. Allow the fish to rise to room temperature before grilling.
Grill the fish over direct heat with the hood closed, starting with the skin side up. Do not turn the fish until it has curled away from the grill grate . At this time it is ready to release itself, and you can check to see if the fish is nicely browned. Once browned (at least 5 minutes and as many as 10), turn the fish over and continue grilling over direct heat with the skin side down and the hood closed.
Sea bass, unlike some fish such as salmon or tuna, tastes best off the grill when it is fully-cooked. Sea bass is cooked through when the meat flakes easily under pressure. It should still be moist. For thicker fillets of 1 1/2 inches or more, you should move the fish to a lower temperature or indirect cooking zone after the first 15 minutes on the grill if it is not yet done.
Once cooked, divide the fillet onto four plates. Stir the blackberry balsamic reduction and then drizzle the plated fish. Garnish with fresh blackberries.
