Verjuice (verjus) is the slightly sweet, slightly acidic juice of unripened wine grapes. It is bottled like wine or vinegar but it is neither fermented nor does it have an alcoholic content.
It is one of those additional flavors ideal for preparations without a lot of ingredients. In that kind of recipe, the goal is allowing the few things you put in to really shine, to be unique or to have some special quality that takes a simple dish to the next level. Verjuice makes food taste great, sort of inexplicably so. With its interesting yet subtle flavor and many familiar uses, it is a gem to keep around the kitchen, and not at all difficult to get the hang of.
The word verjuice is derived from the word pairing 'vert jus' or 'green juice' meaning the liquid pressed from unripened wine grapes. It will last for several years unopened, deepening in fruitiness and color while it ages. Once uncorked, it has only a few months to last in the refrigerator since it is an unfermented product and does not have the same stability as a fermented one. Its applications are wide and open to creativity. When used to deglaze the pan after roasting or sauteing meat or vegetables, the natural sugars help caramelize the leftover bits beautifully. In salad dressings, verjuice will not compete with wine being served, unlike vinegar or lemon which infamously sour the palate. The lightness of flavor brightens soups, sauces and in my recipe-tweaking opinion, it goes swimmingly well with seafood. Dishes that normally call for white wine benefit quickly from the fruity, slightly tart roundness without having to 'cook out' any of the alcoholic essence. I also like to splash some into the pan when wilting greens or as a part of a marinade. Not only a real winner for savory courses, it can be used to poach fresh fruit or glaze a tart when buddied up with some sugar and to macerate stone fruits or berries before they meet their dessert destiny.
Verjuice is not a new ingredient. Its appearance in cooking dates back to the 1300's. Now it is making a comeback for its merits of playing nicely with wine as well as the many above-mentioned uses. Prevalent historically in European and Middle Eastern cooking, it was an Australian chef, Maggie Beer, who was credited with bringing it back to modern kitchens. She bottles and sells her own from the Barossa Valley of her country but most wine producing regions have their versions too: California, France, Italy (where it is called agresto), South Africa and Long Island, New York, a personal favorite. Like everything, verjuice can be purchased online but also look out for it in wine shops and gourmet groceries in your area.
Oh, and sometimes people just drink it as is... or maybe on the rocks. Enjoy!