- In a saucepan combine grapefruit juice, sugar, and cinnamon.
- Bring to boiling; reduce heat. Simmer, uncovered, for 5 minutes.
- Discard cinnamon; cool syrup. Cover and chill syrup.
- Fill four 8-ounce glasses with ice.
- Add about ⅓ cup grapefruit syrup to each glass.
- Fill glasses with ginger ale. Stir gently.