Preheat the grill for direct grilling, high heat. Combine the beer, caraway, coriander, mustard seeds, onions, garlic and ginger in a large stockpot. Then, add the bratwurst. Place the pot on the grates of the grill and bring to a simmer. Simmer the sausages until half-cooked, about 5 minutes. Remove the pan from the grill and let the bratwurst sit in the liquid for 30 minutes. Transfer the brats to a platter or cutting board and strain the liquid into a bowl, discard the solids. Brush the sausages with canola oil and grill until the casings are crisp and golden brown and the sausages are cooked through, 4 to 6 minutes per side. Keep warm until serving.