Split sauce

What an emulsion is, and what breaks it

Fat and water do not mix. An emulsion is fat broken into droplets so small that they stay suspended in water, held there by an emulsifier — egg yolk in mayonnaise and hollandaise, milk proteins in cream, starch in a pasta sauce.

It is an unstable arrangement kept in place by that emulsifier, and three things overwhelm it. Heat, which makes droplets move faster and collide until they merge, and which can cook the emulsifier itself. Too much fat too fast, which gives the emulsifier more than it can coat. And not enough movement, which lets droplets sit together long enough to join.

Once droplets merge into pools, the sauce is split. Rebuilding it means starting a fresh, stable emulsion and adding the broken one to it slowly — which is the principle behind every rescue below.

Rescues, by sauce

All of them work the same way: a small amount of something stable, with the broken sauce whisked into it drop by drop.

Mayonnaise

Put a fresh egg yolk, or a teaspoon of mustard, or a tablespoon of warm water in a clean bowl. Whisk the split mayonnaise into it very slowly, starting a drop at a time.

Hollandaise or béarnaise

A tablespoon of hot water, or a fresh yolk, in a clean bowl. Whisk the split sauce in gradually. If it split because it got too hot and the egg scrambled, it cannot be saved.

Butter sauce (beurre blanc)

Reduce a tablespoon of cream or of the acid base in a clean pan, then whisk the split sauce in off the heat, a little at a time.

Cheese sauce gone grainy

A splash of milk or evaporated milk and hard whisking. A pinch of cornflour or a teaspoon of mustard helps hold it.

Cream sauce

Usually fixable with a splash of fresh cream and gentle heat. A stick blender helps.

Yoghurt in a curry

Not fully fixable. A stick blender homogenises it; a spoonful of cream improves it. It will taste fine.

Vinaigrette

It is meant to separate. Whisk or shake it again, or add mustard, which holds it together for far longer.

Preventing it

• Control the heat. Most splits are heat. Take pans off the burner; use a bain-marie for hollandaise; never boil a sauce with egg or yoghurt in it.
• Add fat slowly at the start. The first quarter of the oil in a mayonnaise is where it is made or lost. After that you can pour faster.
• Keep everything at similar temperatures. Cold oil into warm yolks, or cold cream into a hot pan, both destabilise.
• Use an emulsifier. Mustard in a dressing, egg yolk in a butter sauce, starch or pasta water in a pan sauce, a little cornflour with cheese.
• Keep whisking. Movement is what keeps droplets apart.
• Add acid before dairy, not after — acid tipped into cream will curdle it.

Rebuilding a split emulsion, in general

The technique is the same whatever split.

1. Take everything off the heat and let it cool slightly.
2. Put a small amount of a stable base in a clean bowl — a fresh yolk, a spoonful of hot water, a little cream, or a teaspoon of mustard.
3. Whisk that base until it is smooth.
4. Add the split sauce a few drops at a time at first, whisking constantly. This is where patience decides the outcome.
5. Once it has clearly taken and looks glossy, you can add the rest in a thin stream.
6. If it splits again, you added too fast. Start over with a fresh base.

Common questions