Add the red wine vinegar, apple cider, sugar, bay leaf, cloves, juniper berries, and salt. Bring the liquids to a boil, then cover and reduce heat to a simmer.
3 Tablespoons red wine vinegar, 1 cup apple cider or apple juice, 1 Tablespoon granulated sugar, 1 bay leaf, 2 whole cloves, 2 juniper berries, 1/2 teaspoon salt