- 1/4 cup sugar
- 6 fresh rosemary sprigs, plus more for serving
- 6 strips grapefruit zest, removed with a vegetable peeler
- 6 cups grapefruit juice (from 12 grapefruits)
- seltzer, for serving
- Muddle the sugar, rosemary, grapefruit zest, and ½ cup of the grapefruit juice in a bowl until the sugar dissolves. Add the remaining 5½ cups of juice and chill, 4 hours and up to 24 hours in advance.
- Strain. Serve chilled over ice, topped with the seltzer and a sprig of rosemary.