Soak the gelatine. Peel a grapefruit. Remove white skin. Cut off four thick slices and cut the rest into pieces. Squeeze the rest of the grapefruit. Measure out 1/2 litre fruit juice.
Add apple juice and season to taste with sugar. Heat the juice, squeeze the gelatine and dissolve in it. Put one slice of grapefruit on each wooden skewer. Place them on the glasses. Pour jelly into the glasses.
Refrigerate for one hour. Before serving, carefully pull out the skewers. Decorate jelly with grapefruit pieces and lemon balm.