The balsamic vinegar reduction that I made a few months ago has solidified. It has been refrigerated. Can I heat it to liquefy it and still use it?
Balsamic vinegar should not need storage in a refrigerator, just in a cupboard away from light and in an air tight container.
I would warm the balsamic vinegar by leaving it to warm in at room temperature, covered with a tea towel. If you want to speed up this process I would suggest putting it into a pan or warm water and then reduce it again.