In a saucepan combine the wine, the sugar, and 1 cup water and bring the mixture to a boil, stirring until the sugar is dissolved. Simmer the syrup for 5 minutes and let it cool. In a blender or food processor puree the grapes with the syrup and strain the puree through a fine sieve into a bowl, pressing hard on the solids. Stir in 1 cup cold water and the lemon juice and chill the mixture, covered, until it is cold. Stir the mixture, transfer it to 2 metal ice cube trays without dividers or a shallow metal bowl, and freeze it, stirring with a fork every 20 to 30 minutes and crushing the large frozen clumps, for 2 to 3 hours, or until it is firm but not frozen solid. Scrape the granita with a fork to lighten the texture and serve it in chilled bowls.