Vinaigrette

What it is

The simplest and most familiar emulsion: oil and an acid (vinegar or citrus) beaten together, seasoned, and used as a dressing. Most vinaigrettes are temporary emulsions that separate within minutes; with the right emulsifier and method they can be made stable enough to hold.

The science

Oil and vinegar carry essentially no emulsifier, so whisking them merely creates a temporary dispersion that quickly coalesces and separates — the classic "broken" salad dressing you re-shake before each use. Adding mustard transforms it: mustard contains mucilage (and some surface-active compounds) that coats the oil droplets and slows their merging, turning a fleeting suspension into a creamy, clingy, semi-stable emulsion. The standard ratio of about 3 parts oil to 1 part acid isn't chemistry so much as palate balance, but the method — slow oil addition into the acid-plus-emulsifier while whisking — follows the same droplet-by-droplet logic as mayonnaise, just with a weaker emulsifier and far more acid.

How it's done

Whisk the acid, salt, and a spoon of mustard (and any aromatics) together first, then drizzle in oil while whisking to build the emulsion; or shake everything hard in a sealed jar for a quick temporary version. Emulsifying before adding delicate leaves keeps the dressing clinging rather than pooling. For extra stability, a touch of honey, an egg yolk, or a little of the mustard's mucilage-rich whole-grain version helps.

When to use it

For dressing salads, marinating, and finishing vegetables, fish, or grains. Choose a temporary vinaigrette (shaken, no mustard) when you want a clean, sharp, separated dressing; a stable one (mustard-emulsified) when you want a creamy dressing that coats evenly and stays mixed on the plate.

What goes wrong

A vinaigrette that separates isn't broken so much as temporary by design — re-whisk or re-shake. Genuine problems: too much acid (harsh, puckering — adjust the oil ratio or add a pinch of sugar), a greasy mouthfeel (over-oiled or under-acidified), and a dressing that won't cling (skipped the mustard or added oil too fast). Emulsifying too vigorously with a blender can over-thicken a mustard vinaigrette into something closer to a creamy sauce — fine if intended.

Regional & cultural variations

The French vinaigrette (Dijon mustard, wine vinegar, oil, shallot) is the template; Italian dressings often skip mustard for a looser oil-and-vinegar or lemon style; Japanese dressings emulsify with sesame paste or miso; many cultures build the same temporary oil-acid balance with local fats (mustard oil, sesame oil) and acids (rice vinegar, lime, tamarind, verjus). The emulsifier — mustard, sesame paste, miso, egg — is the regional fingerprint.

Cultural & historical context

Oil-and-vinegar dressing is ancient and near-universal wherever both ingredients existed; the French codification with mustard and shallot turned a peasant dressing into a precise technique. Dijon mustard's role made the difference between a dressing you must shake constantly and one that holds — a small, practical victory of food science achieved long before anyone named the mucilage responsible.

Reference notes

Cross-link to: The Emulsion, Mayonnaise (the stable, oil-dominant cousin), Aioli. Ingredient ties: oil, vinegar/citrus, mustard (emulsifier), honey/egg (stabilizers), shallot. Concept ties: temporary vs. stable emulsion, mucilage, oil-to-acid ratio.

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