In a saucepan combine cranberry juice and balsamic vinegar. Bring to boiling; reduce heat. Simmer, uncovered, for 45 minutes until mixture is reduced to 1-1/3 cups. In a bowl toss together cranberries and sugar; add to juice mixture. Simmer 5 minutes more or until cranberries begin to pop. Remove from heat. Cool. Pour into jar; cover. Refrigerate up to 2 weeks. Makes 20 (1-tablespoon) servings.