Emulsions: Dressings, Mayonnaise and Split Sauces

Oil and water do not mix, but they can be persuaded to: beaten into tiny droplets and held apart by an emulsifier, they make a smooth, thick sauce. Vinaigrette, mayonnaise, hollandaise and a buttery pan sauce all work this way.

Emulsifiers

Egg yolk is the strongest, which is why it carries mayonnaise and hollandaise. Mustard, honey, garlic paste and a little of the starchy water from pasta all help too.

A vinaigrette with a teaspoon of mustard stays mixed far longer than one without.

Slowly at first

The emulsion has to be started with only a little oil. Add the first of the oil a few drops at a time, whisking all the while, until the sauce thickens; after that it can go in as a thin stream.

A rough guide for vinaigrette is three parts oil to one of vinegar or lemon juice, but taste it on a leaf: a dressing that tastes sharp on a spoon is often right on a salad.

Temperature

For mayonnaise, have the yolk and oil at room temperature. Cold ingredients are reluctant to emulsify.

Warm sauces such as hollandaise split when they get too hot, as the egg begins to scramble. Cook them over a gentle heat, and take them off as soon as they thicken.

When a sauce splits

A split mayonnaise looks greasy and curdled. Put a fresh yolk, or a teaspoon of mustard, or a spoonful of warm water, in a clean bowl and whisk the split sauce into it a little at a time. It will come back.

A split hollandaise can be rescued the same way with a spoonful of hot water, whisked in off the heat.

A butter sauce that has turned oily can sometimes be brought back by whisking in a splash of cold water or cream.

Olive oil

Strong extra virgin olive oil can turn bitter when whisked hard, especially in a blender. For mayonnaise use a neutral oil, or mostly neutral with a little olive oil stirred in at the end.