Verjus

Verjus (French for "green juice," also spelled verjuice) is the tart, un-fermented juice pressed from unripe grapes harvested weeks before the wine vintage. Pale green or, from red grapes, a soft rosé pink, it is a gentle souring agent — sharp but not harsh — that sits between vinegar and lemon in the cook's toolkit. Because its acidity comes from grape acids rather than acetic acid or citrus, it brightens a dish without the aggressive bite of vinegar or the perfume of lemon, and, crucially, it is wine-friendly where vinegar and citrus are not.