To make a pineapple jug, cut the top off a medium pineapple. Using a metal serving spoon, hollow out the pineapple reserving the flesh and juice. You might need to cut the core with a sharp paring knife to remove it.
Place pineapple, lychees, lime juice, sugar syrup and rum (if using) in the jug of a blender and process until smooth. Strain the mixture into a jug.
Fill two hollowed out pineapple with half of the pineapple mixture each. Add half a cup of ice to each pineapple. Top the rest with the SodaStream sparkling water. Garnish skewers with lychees and pineapple cubes. Top with fresh mint and a sprinkling of salt. Enjoy chilled by the pool or under the shade of a tree.