Combine first 3 ingredients in a saucepan; stir well. Bring to a boil; cook 1 minute or until sugar dissolves, stirring constantly. Remove from heat; pour into a large bowl, and stir in grapefruit rind. Let cool to room temperature.
Add grapefruit juice and sparkling wine to sugar mixture. Pour mixture into the freezer can of an ice-cream freezer; freeze according to manufacturer's directions. Spoon into a freezer-safe container; cover and freeze 2 hours.