Is there a science to keeping a dressed salad crisp and fresh?
Ever notice that sometimes salads seem to go limp as soon as the dressing hits the leaves, while other times they stay crisp and crunchy, even when they sit around for some time? We wondered if there is something about how a salad is dressed that can keep it fresh or cause it to sog out more quickly.
We dressed 2 ounces of mixed salad greens in three ways: tossed with oil and then vinegar; tossed with vinegar and then oil; and tossed with a fully emulsified dressing made with vinegar, oil, and a little bit of mayonnaise and mustard (the latter ingredients keep the emulsification stable much longer than vinegar and oil alone). We waited 15 minutes and then examined the greens for signs of wilting.
The first salad was seriously wilted after 15 minutes; the second salad was a little wilted; the third salad was barely wilted at all.
It turns out that salad leaves have a protective waxy cuticle layer that prevents water-based liquids (vinegar) from having much effect on them, but oil easily penetrates this film. Tossing the greens with vinegar first provides a barrier that blocks the oil, keeping it from penetrating the cuticle. The emulsified vinaigrette works the best at keeping the salad crisp because in this state the vinegar surrounds droplets of oil, keeping them trapped and preventing contact with the greens.
Tossing a salad with a fully emulsified vinaigrette (bottom) is the only way to ensure that greens keep their crisp texture. But if you prefer to add oil and vinegar separately, introduce the vinegar first, followed by the oil (middle).