Granitas are coarse ices, which are prepared by freezing coffee, wine, juice or other liquid and scraping ice crystals with the tines of a fork. Shirley O. Corriher, whose cookbook Cookwise is a textbook for Culinary Institute of America students, explains that sugar is the key to the texture of an ice. If you decide to omit the Kahlúa, increase the sugar to ½ cup as this maintains the proper sugar percentage in the dessert.
2 cups cool brewed espresso or strong coffee
1/3 cup and 2 tablespoons sugar
2 tablespoons Kahlúa or other coffee liqueur
¼ teaspoon finely grated lemon zest
¼ teaspoon finely grated orange zest
1 cup heavy or whipping cream
Stir together espresso, 1/3 cup sugar, Kahlúa and zest. Refrigerate at least an hour to chill well. Pour into a metal or plastic pan or bowl and place in the freezer. When ice crystals begin to form around the edge, stir well every 15 minutes until completely frozen. Fluff crystals lightly with a fork and leave in freezer to dry for about an hour before serving.
From Cookwise by Shirley O. Corriher (William Morrow 1997).