In a Dutch oven, cook bacon over medium heat for 5 minutes. Add onion; cook and stir until tender, 6-8 minutes. If desired, stir in liquid smoke., Add cabbage, water, vinegar, apple, sugar and salt. Bring to a boil; reduce heat. Simmer, covered, until cabbage is crisp-tender, about 20 minutes, stirring every 10 minutes. Serve with a slotted spoon.