Put the sugar with the water in a small saucepan and reduce to a sugar syrup.
Put grapefruit juice and lemon juice through a sieve in a bowl. Mix with the grenadine syrup and vodka. Mix the cooled sugar syrup into the juice. I used 100 ml of sugar syrup because my grapefruit were very sweet. Put the mixture in the fridge for 1 hour and then freeze in the ice cream maker.
Presentation: Pour sorbet into champagne bowls and pour vodka over them.
Serve sprinkled with the candied cirtus fruit cubes and chopped pistachios.