Put the broth, beets and potatoes in a large heavy-bottomed pot and bring it to a boil, then reduce the heat to a simmer. Cover and cook until the vegetables are just tender, about 20 minutes. Uncover and stir in the cabbage and red wine vinegar. Season, to taste, with salt and pepper (taste for sodium levels in the broth before salting). Simmer for another 15 minutes, stirring occasionally. Ladle the soup into serving bowls and serve warm. Enjoy!