MODENA — This summer, Aceto Balsamico di Modena IGP (Modena’s protected balsamic vinegar) has moved from the cheese board to the cocktail shaker, as bartenders across Europe give the vinegar a starring role, from a London whiskey highball to a strawberry Negroni riff.

There is a moment every chef knows, the one where a splash of acid rescues a dish that was merely OK a second before. That instinct has now wandered behind the bar, turning up in cocktails from London to Denver this summer.