White Rum and Grapefruit Cocktail

Ingredients

• • 2 cups (500 ml) pink grapefruit juice, cold
  • 1/4 cup (60 ml) white rum
  • 1 tablespoon (15 ml) sugar
  • 1/2 egg white
  • 1/2 teaspoon (2.5 ml) orange blossom water
  • cold tonic water, to taste
  • 4 small sprigs fresh rosemary