Zest one of the grapefruit directly into a small saucepan

Cut a thin slice off the top and bottom of each grapefruit with a small serrated knife. Working from the top of the fruit to the bottom, follow the curve of the fruit to cut away peel and white pith

Working over a bowl to catch the juices, use a paring knife to slice along one side of each segment, separating it from the thin membrane. Slice down the other side to remove the whole segment. Repeat with the remaining segments and set aside the grapefruit with its juice

In a large saucepan combine 360mls water, the agave, sugar, zest, ginger, cinnamon and star anise. Bring to a boil and stir to dissolve the agave and sugar, then reduce the heat and simmer uncovered for 10 minutes

Remove the cinnamon sticks, star anise (& ginger if you like, I prefer to leave it in) with a slotted spoon

Add the grapefruit segments with their juice and cook at a very gentle simmer for 2 to 3 minutes. Using a slotted spoon transfer the grapefruit segments to a bowl and set aside

Spoon the syrup over the grapefruit segments. Cover and chill for 1 hour before serving.