DRESSINGS

THERE ARE TWO TYPES OF COLD SAUCES typically used to dress salads. Vinaigrette is a relatively thin emulsion made of oil, vinegar, and seasonings. Mayonnaise is a thick, creamy emulsion of egg yolk and oil with a little acid and some seasonings.

An emulsion is a mixture of two things that don't ordinarily mix, such as oil and water, or oil and vinegar. The only way to mix them is to stir or whisk so strenuously that the two ingredients break down into tiny droplets. Many of these droplets will continue to find each other and recoalesce into pure fluid. (This is what happens when the emulsion breaks.) Eventually one of the fluids (usually the less plentiful one) will break entirely into droplets so tiny that they remain separated by the opposite fluid, at least temporarily.

The liquid in the droplet form is called the dispersed phase because the droplets are dispersed throughout the emulsion. The liquid that surrounds the droplets is the continuous phase. Because the continuous phase forms the surface of the emulsion, that's what the mouth and tongue feel and taste first.

Vinaigrette is the most common dressing for salads, used with leafy greens as well as vegetables, grains, and beans. While it is possible to dress a salad with oil and then vinegar, the results are quite different when these ingredients are combined before being poured over greens.

To demonstrate this difference, try this test. Dress a simple green salad first with oil, then a mixture of vinegar, salt, and pepper. The result will be harsh, with an extremely prominent vinegar bite. Next, take another batch of greens and the same dressing ingredients. Mix the salt and pepper into the vinegar and then whisk in the oil until the dressing is translucent. When this emulsified dressing is poured over greens, the flavor will be smoother with a greater emphasis on the oil.

The science of emulsions explains why the same ingredients can taste so different. In the first oil-then-vinegar salad, the oil and vinegar don't mix, so both race up the tongue. The less viscous vinegar wins, hence this salad taste more acidic. In the emulsion, the oil is whipped into tiny molecules that surround dispersed droplets of vinegar. The oil is the continuous phase and is tasted first. Your tongue is coated with fat droplets that cushion the impact of the acid.

The correct ratio of oil to vinegar is open to much discussion and can depend on the acidity of the vinegar as well as the flavor of the oil. In general, we prefer a ratio of four parts oil to one part acid, but this can vary, especially when using citrus juices and rice wine vinegar, which are much less acidic than common vinegars.

In terms of forming a vinaigrette, either a fork or small whisk will generate the whipping action necessary to break up the oil into small droplets. With either tool, the emulsion will break rather quickly so rewhisk the dressing just before pouring it over salad greens. We found that adding the salt and pepper to the vinegar is best because the vinegar mutes these flavors a bit and prevents them from becoming too overpowering. On the other hand, we prefer to add herbs and some other seasonings to the finished dressing to maximize their impact.

Mayonnaise is used to dress vegetable salads—especially potato salad and coleslaw. It acts as a creamy binder and adds richness to any salad. The science of mayonnaise is fairly complex and unusual. Whisking transforms three thin liquids—vegetable oil, lemon juice, and egg yolk—into a thick, creamy sauce. In this sauce, the egg yolk and lemon juice are the continuous phase (that's why something that is 95 percent oil doesn't taste greasy) and the oil is the dispersed phase that must be broken into tiny droplets.

Mayonnaise works because an egg yolk is such a good emulsifier and stabilizer. But sometimes mayonnaise can "break," as the ingredients revert back to their original liquid form. To keep mayonnaise from breaking, it is first necessary to whisk the egg yolk and lemon juice thoroughly (the egg yolk itself contains liquid and fat materials that must be emulsified). It is equally important to add the oil slowly to the egg yolk. Remember, two tablespoons of yolk and lemon juice must be "stretched" around ³/₄ cup of oil.

In terms of oil, we like the flavor of corn oil in our basic mayonnaise. It produces a dressing that is rich and eggy with good body. Canola oil makes a slightly lighter, more lemony mayo. We find that extra-virgin olive oil can be harsh and bitter, especially if used alone in mayonnaise. Pure olive oil produces a mellower mayonnaise but is more costly than corn or canola oil and does not deliver better results.

While homemade mayonnaise is a delicious addition to salads, many cooks prefer the convenience and safety of commercial brands made without raw eggs. In our tasting of major brands, Hellmann's came out on top. Among light or reduced-calorie brands, Hellmann's again beat out Kraft, which is its main competition in the marketplace.

GLOSSARY OF OILS AND VINEGARS

The following oils and vinegars are used in recipes throughout this book. To keep oils from becoming rancid, store bottles in a cool, dark pantry and buy small quantities that will be used up within a few months. Storing oils in the refrigerator will prolong their freshness.

EXTRA-VIRGIN OLIVE OIL: This is our standard choice for most salads. In blind tastings, we could not tell the difference between extra-virgin oil that cost $10 per liter and $80 per liter. However, cheaper pure and "light" oils are characterless and decidedly inferior in salads, although they may be fine for some cooking. An inexpensive supermarket extra-virgin oil, such as Berio or Colavita, is our recommendation for salads.

WALNUT OIL: This oil has a warm, nutty flavor that works well in salads with fruits and/or toasted nuts. Like other nut oils, walnut oil tends to go rancid quickly and is best stored in the refrigerator.

ASIAN SESAME OIL: With its dark brown color and rich aroma, toasted sesame oil adds a distinctive Asian flavor to salad dressings. Use it in moderation. More than a tablespoon or so will overwhelm other ingredients.

CANOLA OIL: This bland oil is best used to soften a particularly strong oil, especially sesame or walnut. Alone, its flavor is unremarkable. But in combination with a potent nut or seed oil, canola can be part of a good dressing.

RED WINE VINEGAR: Red wine vinegar is the most versatile choice in salads. Its flavor is sharp but clean. Domestic brands tend to have an acidity around 5 percent, while imported red brands often contain as much as 7 percent. In our tasting of red wine vinegars, Heinz beat other domestic brands as well as imports, some of which cost ten times as much.

WHITE WINE VINEGAR: Similar to red wine vinegar but often not quite as complex. Our choice when a pink vinaigrette made with red wine vinegar might seem odd.

BALSAMIC VINEGAR: A rich, sweet, oaky vinegar that is best used in combination with red wine vinegar in salads. Real balsamic vinegar is aged many years and costs at least $10 per bottle. Cheap supermarket versions are nothing more than caramel-colored red wine vinegar. They are usually harsh and unpleasant tasting. Given the small quantities of balsamic vinegar needed to transform a salad, it's worth investing in the real thing. In our tasting, we liked vinegars from Cavalli, Fiorucci, Fini, and Masserie di Sant'Eramo.

SHERRY VINEGAR: This Spanish vinegar is usually quite strong (often with 7 percent acidity) but has a rich, oaky, nutty flavor.

CITRUS JUICES: Orange, lime, and lemon juices can all be used in salad dressing. They add acidity as well as flavor. Lemon and lime juices are more acidic and can stand on their own. Orange juice is usually combined with vinegar. To add more citrus flavor without disturbing the ratio of acid to oil, stir in some grated zest.

RICE WINE VINEGAR: A natural choice in Asian dressings, this low-acidity (about 4.5 percent), clear vinegar is quite mild. Use it when you want to keep acidity in check but want to avoid the distinctive flavor of citrus juices.