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Sauces

Emulsions: vinaigrettes, mayo, and why they break

A classic vinaigrette is three parts oil to one part acid — and that 3:1 ratio, plus an emulsifier, is what keeps it from separating the second it hits the salad. Emulsions force two ingredients that hate each other, oil and water, into a stable, creamy mixture. Once you understand the mechanism, you can make a dressing, a mayonnaise, or a glossy sauce on demand.

By Josh Strauss, Mise Kitchen Team · Published

How an emulsion holds

Oil and water naturally separate. An emulsion suspends tiny droplets of one inside the other and keeps them apart with an emulsifier — mustard, egg yolk, or honey — whose molecules grab both oil and water at once. Vigorous mixing breaks the oil into small enough droplets for the emulsifier to coat. No emulsifier, or droplets too big, and it separates.

A vinaigrette that stays together

The 3:1 oil-to-acid ratio is the starting point; adjust to taste.

  1. 1
    Start with acid and emulsifier. In a bowl or jar, combine the acid (vinegar or citrus) with a teaspoon of mustard, plus salt and pepper.
  2. 2
    Add oil slowly. Whisk constantly while drizzling the oil in a thin stream so it breaks into fine droplets the mustard can hold.
  3. 3
    Check the texture. It should look creamy and slightly thickened, not layered. Taste and balance with more acid or salt.
  4. 4
    Re-emulsify as needed. If it sits and separates, just whisk or shake it again before serving.

The same trick, scaled up

Mayonnaise is the same idea with egg yolk as the emulsifier and far more oil. Hollandaise (one of the five mother sauces) is a warm emulsion. And finishing a pan sauce with cold butter is a quick emulsion that gives it gloss. Once you see emulsification, you spot it everywhere.