Peel the grapefruit and two oranges so that the white skin is completely removed. Cut the fillets out of the parting skins, collecting the juice. Squeeze the rest of the orange. Mix grapefruit and orange juice with Campari and vanilla sugar. Wash pear and apple thoroughly, cut into quarters and remove seeds.
Cut pear into slices, apple into pieces. Mix pear, apple, grapefruit and orange. Pour the marinade over it and let it stand for about 30 minutes. Garnish fruit salad with lemon balm