For the flavor base: To a large pan with straight sides or a stockpot, add the beer, sugar, vinegar, red pepper flakes, liquid smoke, garlic and peppercorns. Turn the heat to medium high and stir to dissolve the sugar.
For the braise: Stir in the onions and cabbage. Heat until the liquid begins to boil. Turn down the heat and allow the vegetables to simmer, stirring occasionally, until the cabbage is tender, 35 to 45 minutes. Serve warm or chilled.