The best quality balsamic vinegar can be over 100 years old but is more commonly sold at three to four years of age. True balsamic vinegars are very expensive but have an exceptional flavour.
The temperature will rise about 10F during this time. 5) Make the Sauce: - Boil balsamic vinegar in a small saucepan for 20 minutes until reduced to 1/4 cup. - Mix butter and flour into a paste.