Wash the grapefruit, dry, and cut in halves crosswise.
Remove seeds with a fork and then cut around each fleshy section with a sharp curved knife, separating the flesh from the pulpy membranes.
With scissors, cut down each membrane from edge to core.
Insert knife again and separate core from fruit shell.
With scissors or fingertips lift the center, bringing the membrane with it, and leaving fruit sections intact.
If sugar is to be added put 1 tsp.
In the center of each prepared grapefruit half and let stand 10-15 min. in a cold place before serving.