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At their simplest, vinaigrettes are a mixture of oil and vinegar, spun together with some arm power and a whisk to make a cohesive sauce. But a vinaigrette made with only oil and vinegar can quickly split back into its two separate parts, turning each bite of salad into a surprise: Will it be oily or acidic?
The best vinaigrettes are ones that stay together. We turned to the kitchen—and to science—to find out how to keep them that way.
The key to foolproof vinaigrettes has everything to do with the principle of emulsification. An emulsification is a combination of two liquids—like oil and vinegar—that don’t mix on their own.
But with strenuous whisking, the liquids break down into droplets, one liquid eventually breaking down into such tiny droplets that it is completely surrounded by the other, effectively making the two liquids into one.
Without any help, these tiny droplets will find each other again with relative ease, separating and breaking and causing an unpleasant salad experience. But help is exactly why we’re here. Help comes in the form of something called an emulsifier—like egg yolk, mustard, or mayonnaise.
Emulsifiers help the vinegar and oil combine into a unified sauce and stay that way. How do they work?
Well, let’s take egg yolk. Egg yolk contains lecithin, a phospholipid. The lecithin molecule has two ends. One end is attracted to water (also called hydrophilic) and the other end is repelled by water (called hydrophobic) but is compatible with oil. This means that when egg yolk is added to a mixture of oil and vinegar, the hydrophilic ends of lecithin dissolve into the vinegar and the exposed hydrophobic ends form a little shield around the drops of oil. Two things happen here:
First, the oil droplets become surrounded by the vinegar, and not the other way around. Second, because the oil droplets are protected by this coating of emulsifier, they stay separate for far longer than they would alone. Adding an emulsifier to a vinaigrette, then, keeps it together for far longer.
But the real question, we wondered, was which is the best emulsifier? To tease out the relative effectiveness of these three common emulsifiers, associate editor Dan Souza made four vinaigrettes (one per emulsifier, plus a control), using four stand mixers each fitted with the whisk attachment to ensure that the ingredients received the same amount of whisking.
He added ¼ cup of vinegar to the bowl of each mixer and added then 1 tablespoon of mustard to one, an egg yolk to the second, and 1 tablespoon of mayo to the third. To the fourth, he didn’t add any emulsifer at all. He ran the mixers on medium speed and poured ¾ cup of oil into each.
Then Dan sat back and watched.
The vinaigrette with the egg yolk was clearly the most stable. It was still together after 3 hours. The one with mayo began to break after 1½ hours. The one with mustard began to break after a half-hour. The dressing without an emulsifier? That was completely broken after only 15 minutes.
Control breaks after only 15 minutes.
Mustard vinaigrette breaks after 30 minutes.
Mayo vinaigrette breaks after 1½ hours.
Egg yolk vinaigrette completely emulsified.
The winning emulsifier would be clear if we were judging by time alone. But taste plays a role, too. And the egg yolk gave the dressing an eggy flavor that tasters didn’t like. The mayo didn’t add much flavor, but was creamy, which was nice. The mustard? That tasted by far the best.
So, with science on our side, we can safely say that the key to a foolproof salad dressing is to use an emulsifier. In the test kitchen, we leave the yolk behind and instead choose a combination of mayo and mustard. Neither emulsifier was the most effective. But adding raw egg yolk to a salad isn’t for everyone. And mayo, which contains some egg yolk, still has great emulsifying power. Mustard boosts stability and also adds some good flavor. Together? Perfect.
MAKE IT NOW. Our recipe for Foolproof Vinaigrette is free through December 17, 2012.
Do you have any burning question on emulsifiers? Leave 'em in the comments.