Here's a question nearly as divisive as Yanny or Laurel*: When you set out to dress a pile of greens, do you drizzle first with the olive oil or with the vinegar? (Have you ever considered the order of operations at all?)
At the tiny café where I cook, nary a green goes undressed. We wouldn't dare send out an herb salad without a slick of olive oil and a drip of white wine vinegar—and for that matter, we wouldn't serve sliced avocado without olive oil and soy sauce, or cubed Asian pear without lemon juice, vinegar, and a crumbling of flaky salt. In the philosophy of the chef for whom I work, there's almost no food that can't be improved upon with the right sort of dressing—and an art to the sequence: First comes love, then comes marriage olive oil, then comes vinegar, he has instructed me (and yes, both come from squeeze bottles). Otherwise, the oil will simply slide off, pooling below its intended landing spot.
But wait just one second! Superstar recipe developer Melissa Clark, for one, recommends the opposite order: Season with salt, then dress with vinegar in order to dissolve the salt for a more evenly seasoned salad. And the authoritative Italian cookbook Il cucchiaio d’argento affirms Clark's order: start with salt, follow with vinegar, finish with oil.
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Lest the debate be put to rest so easily, let's turn to Marcella Hazan, who sides with my chef-boss. In her seminal book Essentials of Italian Cooking, she writes: "Add the vinegar last, just the few drops necessary to impart aroma, and never more than one skimpy part vinegar to three heaping parts oil." Why is it important to finish, rather than begin, with the vinegar? According to Hazan, "the acid of vinegar, like that of lemon, 'cooks' a salad, which explains why the oil is poured first, to protect the greens."
And yet—here's the head-scratcher—the vinegar might not be the culprit of wilted or discolored leaves at all. Over on Serious Eats, food science whiz J. Kenji López-Alt found that greens dressed with only oil wilted significantly faster than those dressed with only vinegar. (He actually observed that the vinegary greens were as comparably lively and fresh as the control greens tossed with plain water.) Why? The greens' natural oil coat, López-Alt explains, "makes it very easy for the olive oil to penetrate the spaces between cells" and damage the leaves.
All of this suggests that it's beneficial to dress with vinegar first—you can flavor the leaves while buying yourself some wilt-free minutes—and brings us back to the very beginning (le sigh!).
Turns out that a simple dressing is actually pretty complicated.
I did a few very unscientific tests to figure out if I could discern any difference in oil-vinegar versus vinegar-oil. First, I dressed a sliced avocado. The soy sauce seemed to have more staying power when it was applied before the olive oil (the avocado fan on the right), as I watched it positively cascade off the slices that had already been drizzled with oil (the fan on the left).
But both avocado piles had pools of olive oil and soy sauce below—and there was no discernible difference in taste or appearance.
Onto the next challenge: I dressed two piles of greens with the exact same amount of olive oil and red wine vinegar, but in opposite orders. This time, the difference in taste was apparent: The greens that got dressed with vinegar after olive oil were more, well, vinegary—with distinctly sharp spots, even after my gentle toss. I preferred the greens that had been dressed first with vinegar because they tasted more evenly seasoned to me.
Olive oil first (left) versus vinegar first (right). Looks the same to me!
But my experiments were not yet over! For I ate both piles of greens and found that a lot more olive oil had accumulated on the plate to which it was added second. Perhaps it did slip off the vinegary leaves and onto the plate below?
It appears that much more dressing ended up on the plate—rather than on the leaves—of the salad on the right.
So what, then, is one to do? First, accept that you're probably going to have a less-than-homogenous dressing: Oil and vinegar don't mix, so one or the other is going to slip-slide off your greens or vegetables. If you want a thorough slick of oil (as Marcella says, "enough of it to produce a glass on the surface of the vegetables") apply it first—but know that, in the case of the salad, it's going to wilt the leaves. Eat quickly! If you're more concerned about even seasoning, drizzle in the vinegar first, so it has a chance to penetrate those cells before the oil steals the show.
And if you want a stable dressing where the vinegar won't bead on the surface of the vegetables before falling straight to the bottom of the bowl... well, you should use an emulsifier like honey, mayonnaise, egg yolks, garlic, or mustard. Or turn to a recipe: We've got 50 right here.
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