First of all, what is "Verjuice"? Literally means "Green Juice" is a juice made by pressing unripe grapes and sometimes lemon, herbs or spices are added to change the flavour.

 It was used in many contexts where modern cooks would use either wine or some variety of vinegar, but has become much less widely used as wines and variously flavoured vinegars became more accessible.

Modern cooks most often use verjuice in salad dressings as the acidic ingredient, when wine is going to be served with the salad. This is because verjuice provides a comparable sour taste component.

And did you know that n the regional French of Ard├Ęche, a cider fermented from crab apple juice is called verjus. In medieval and early modern English cookery texts "verjuice" sometimes means apple juice or crab-apple juice.

And the last things, after opening, verjuice must be refrigerated and will keep for up to three months depending on fridge temperature.