Put the pineapple juice, lemon juice, egg white, cherry syrup and almond extract into a blender. Whizz the mixture a few times at a high speed, until the mixture is pale and starting to increase in volume. If your blender is suitable for use with ice, add a few handfuls and pulse twice more to chill the mixture. Alternatively, stir in the ice until the outside of the jug feels cold. Pour into glasses and garnish with the cherries to serve.