Puree grapes, sugar, lemon zest and juice in blender until mixture is smooth. Place mixture in a saucepan and bring to boil over high heat. Let boil 30 seconds, then remove from heat. Strain puree through fine strainer and discard solids. Stir vodka into puree. Let mixture chill in refrigerator, then place in an ice cream freezer according to manufacturer instructions or freeze in a shallow pan, stirring every 10-15 minutes until frozen.
Nutritional analysis per serving: Calories 163; Protein 1 g; Fat 1 g; Calories from Fat 5 %; Carbohydrates 41 g; Cholesterol 0 mg; Fiber 1.6 g; Sodium 3 mg.