Halve the lemon, orange or tangerine, and lime; squeeze out all of the juice. (You should get about 3/4 cup total.) In a small saucepan combine citrus juice and sugar. Add half of the citrus shells. Bring to boiling, stirring until sugar is dissolved; reduce heat. Simmer, uncovered, for 5 minutes. Discard shells.
In a large bowl combine pears, papayas, and grapes. Pour hot syrup over fruit, gently stirring to mix. Cover and chill for up to 4 hours. Before serving, garnish with mint, if desired. Makes 6 servings.
Prepare the syrup and fruit mixture. Cover and chill up to 4 hours.