Open your refrigerator: how many bottles of salad dressing are lurking in the door? If you’re an average American shopper, you add one or two bottles to that sticky collection every couple of months.

Yet you don’t actually need a single one. Those bottled dressings, even the expensive and all-natural versions, contain ingredients like corn syrup, cheap vegetable oil, monosodium glutamate and any number of unnecessary stabilizers and gums.

And they aren’t really more convenient than a basic vinaigrette made from real ingredients — which can also live happily and indefinitely in the refrigerator door. There’s a notion among purists that homemade dressing must be made from scratch for every single salad. These are the same people who scorn salad greens in plastic tubs, wash every leaf individually, and tell you to rub your olive-wood salad bowl with a garlic clove. As Maggie Smith proclaimed in “The Prime of Miss Jean Brodie,” “For those who like that sort of thing, that is the sort of thing they like.”