Pineapple, lime and ginger beer cooler

1. Set 1 lime aside and reserve 30g pineapple. Using a sharp, serrated knife, slice the top and bottom from the other 2 limes, exposing the flesh. Slice down the sides to remove the green zest and white pith, following the curve of the fruit; discard the zest and pith. Blend the lime flesh, the remaining 300g pineapple and a little demerara sugar (depending on the sweetness of the pineapple) in a blender, until completely smooth. For total smoothness, pass through a sieve, pressing with the back of a spoon to release all the juice. Stir in the ginger beer, then serve in tumblers with crushed ice. Slice the reserved lime and pineapple and use to garnish.