A proper vinaigrette— neither too oily nor too acidic—is the difference between a vibrant salad and a pile of wet greens. But reader Heather DiLeo of Brooklyn, New York has struggled to find that balance, wondering whether the secret is the ratio of oil to acid, how you mix the two or how you dress the salad.

To determine the best way with vinaigrettes, we made nearly 30 of them. Basic vinaigrettes contain oil, acid, often salt, sugar and black pepper, sometimes an allium, and an emulsifier (such as mustard or honey) to bind the oil and acid. We quickly learned that the emulsifier is key.

Conventional wisdom says acid wilts greens, but it’s actually the oil that’s to blame: Oil more readily penetrates the greens’ cells. But when bound to other ingredients by an emulsifier— we used Dijon mustard—the oil penetrates the greens more slowly, keeping them fresher longer. To keep the oil from separating, be sure to remix the vinaigrette just before dressing the salad. We like a 3:1 oil-to- acid ratio, but we also learned that the acidity of vinegar is just as important as its volume.

Tasters overwhelmingly preferred relatively low-acid white balsamic vinegar (5.5 percent) over stronger white wine vinegar (7 percent). Also important: order. We got the most even seasoning by dissolving any salt or sugar in the acid before adding the oil. And for vinaigrettes with an allium, that should be added to the acid first, too, to mellow its bite.

Finally, we looked at how to dress the greens. We found the best bet was first drizzling the dressing over the greens in a large bowl, then tossing well.

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