Peel and slice the ginger. Bring the ginger, sugar, liqueur and grapefruit juice to the boil, remove from heat and allow to cool. Remove ginger. Pour the grapefruit mixture into a flat, suitable container and freeze for at least 5 hours, preferably overnight.
Wash the mint, dab dry and put something aside for decoration. Pluck the remaining mint from the stalks and cut into strips. Scrape off granite with a spoon, fold in mint and fill into glasses. Decorate with mint
Waiting time approx. 10 minutes