Combine the sugar, water and grapefruit zest in a medium saucepan and bring to the boil, stirring occasionally, until the sugar dissolves. Remove the pan from the heat and set aside for 5 minutes. Stir in the grapefruit juice and lemon juice. Strain the mixture through a fine-mesh sieve into a clean bowl. Set aside to cool, then cover and refrigerate for 4 hours or overnight. Process the sorbet in an ice cream machine until done. Grapefruit sorbet is a deliciously refreshing end to a lavish dinner, or can also be serve as an in between course palate cleanser. Serve with a sprig of fresh mint in a martini glass or simply in the grapefruit skin shell.
1 ¼ cups sugar
1 ¼ cups water
1 teaspoon grated grapefruit zest
2 cups freshly squeezed grapefruit juice
2 tablespoons freshly squeezed lemon juice