Balsamic vinegar is a dark, glossy, sweet-and-sour Italian condiment made not from wine but from cooked grape must — the boiled-down juice, skins and seeds of pressed grapes. The name covers two utterly different products: rare Aceto Balsamico Tradizionale, a syrupy, decades-aged treasure from Modena and Reggio Emilia, and the cheap, ubiquitous Aceto Balsamico di Modena of supermarket shelves, a thinner blend of grape must and wine vinegar. Both share a hallmark balance of sweetness, bright acidity and woody, mellow depth.