Why sauces break — and how to bring them back

Droplets, held apart

An emulsion is fat broken into droplets so small they stay suspended in water instead of floating to the top. Whisking makes the droplets; an emulsifier — egg yolk, mustard, the milk solids in butter — coats them so they cannot merge back together. Take either one away and the sauce separates.

1. Split
2. Coming together
3. One sauce

Worth remembering Shear makes the droplets. An emulsifier is what keeps them apart.

Too fast is the usual cause

Pour the oil in faster than the whisk can break it up and it arrives as a pool rather than droplets, with no emulsifier left to coat it. That is why every mayonnaise recipe starts drop by drop and only speeds up once the base has thickened — by then there is a working emulsion to pour into.

Worth remembering Slow at the start, faster once it thickens. Never the other way round.

Heat breaks them too

Warm an emulsion past roughly 70 °C and the droplets have enough energy to merge no matter how well they are coated — the butter sauce you built in a warm pan splits into a greasy slick the moment it returns to a simmer. This is why butter is mounted off the heat, and why hollandaise lives over water rather than over flame.

1. Split
2. Coming together
3. One sauce

Worth remembering Off the heat before the butter goes in, and it does not go back on.

Bringing a broken one back

A broken sauce is not lost. Start a fresh base in a clean bowl — a spoonful of cold cream, a new yolk, a splash of the reduction — and whisk the broken sauce into it slowly, as if it were the oil. You are rebuilding the emulsion from scratch using what you already have. It works nearly every time, and it takes about a minute.

1. Runs off
2. Holds a lane
3. Curdled

Worth remembering Never whisk harder. Start a new base and pour the broken sauce into it.