Measure exactly 4 1/2 cups of balsamic vinegar into a 6-quart pan. Stir sugar into the balsamic in the pan. Bring mixture to full rolling boil on high heat, stirring constantly. Stir in pectin. Return to full rolling boil and boil exactly 1 minute.
Skim off any foam. Ladle into jars, seal and process 8 minutes.