Preheat the grill to high. Arrange the onion slices and garlic along the bottom of a medium stockpot. Place the bratwurst on top and then add the beer, water, coriander, caraway, mustard seeds and ginger.
Bring to a simmer over the grill grates or on a burner. Simmer the sausages in the mixture for about 10 minutes. Remove the pan from the heat and let the bratwurst sit in the liquid for 10 minutes.
Remove the sausages with a pair of tongs onto a platter. Remove the onions with a slotted spoon and place in a bowl. Grill the sausages until the casings are crisp and golden brown, about 3 to 4 minutes per side. Serve the bratwurst on the buns with the onions, mustard and sauerkraut, if desired. Garnish with pickles, pickled beets and pickled eggs, if desired.
Red Cabbage Sauerkraut:
1/4 cup olive oil
2 cups red wine vinegar
1 cup water
1/4 cup granulated sugar
1 teaspoon whole mustard seeds
2 cloves garlic, peeled and thinly sliced
1 large head red cabbage, thinly shredded
Salt and freshly ground pepper
Preheat grill to high. In a medium saucepan, combine the oil, vinegar, water and sugar over medium heat, and cook until the sugar has melted. Add the mustard seeds, garlic and cabbage, and cook until the cabbage is soft, about 15 to 20 minutes. Season with salt and pepper to taste.