White grapefruits are tangier than pink ones, so they make this granita an especially good palate cleanser. If you'd like a sweeter granita, use only 3 cups of juice.Plus: More Dessert Recipes and Tips
In a medium saucepan, combine the water with the sugar, star anise and grapefruit zest and bring to a boil. Simmer over low heat for 5 minutes. Remove from the heat and let cool to room temperature, about 1 hour.
Remove the star anise and reserve. Stir in the grapefruit juice. Pour into a 9-by-13-inch baking dish and freeze for 1 hour, or until set around the edges. Using a fork, scrape the ice crystals into the center and freeze again. Repeat the scraping every 30 minutes, until the entire mixture has turned into ice flakes. Spoon into small glasses, garnish with the reserved star anise pods and serve.
The granita can be frozen, covered, for 5 days. Stir before serving.