Place wine in a medium saucepan and bring to a simmer. Reduce heat and simmer over very low heat for 15 minutes. Let cool slightly, then puree with grapes, sugar, vinegar, and lemon juice in a high-speed blender. Pour into a 1-quart freezer-safe glass or plastic dish about the size and shape of a loaf pan. Cover and freeze for 8 hours. Scrape the surface with a fork until mixture is slushy. Return to freezer for at least 4 more hours, then scrape with a fork again until light and icy. Cover and freeze until ready to serve.