Bring the sugar and white wine to a boil then let cool.
Peel the pineapple, core and chop the flesh coarsely. Purée until smooth then measure out 500 ml (approximately 2 cups). Mix the pineapple purée with the wine syrup. Transfer to a shallow container and freeze, stirring occasionally, for 4-5 hours.
Whip the egg whites with the sugar until stiff and carefully fold into the sorbet. Freeze again until solid.
Scoop the sorbet into chilled serving glasses and garnish with pineapple slices.