2 1/2 cups water
1 cup sugar (if you prefer a sweeter sorbet, increase the sugar to 1 1/4 cups)
3 lemons, juiced
1 grapefruit, juiced
In a medium saucepan, combine the water and the sugar. Heat, stirring frequently, until the sugar is completely dissolved. Remove the pan from the heat, then chill thoroughly in the refrigerator. Stir the lemon and grapefruit juice (1 cup total) into the chilled sugar syrup, then freeze the mixture in your ice cream maker.