The two-minute science of a dressing that never splits
Emulsions are not luck. A little mustard, the right order, and enough agitation will hold oil and vinegar together for a week.
Arun Pillai
Executive Chef
5 min read
Oil and vinegar do not want to be together. Left alone they separate within minutes, because water-based and fat-based liquids have no chemical interest in each other. An emulsion is a temporary truce, and your job is to broker it.
The role of mustard
Dijon is not in a vinaigrette for flavour alone. Mustard contains mucilage, a compound with a water-loving end and an oil-loving end. It parks itself at the boundary between droplets and stops them merging back together.
- Whisk acid, mustard and seasoning together first — always
- Add oil in a thin stream while whisking constantly
- A teaspoon of mustard stabilises roughly 100ml of dressing
- Honey and egg yolk work as emulsifiers too, with different results
Get the order wrong — oil first, acid after — and you will chase a broken dressing around the bowl forever. Emulsions form when you introduce the oil slowly into the water phase, not the reverse.
“If it splits, do not throw it out. Start a fresh spoon of mustard in a clean bowl and whisk the broken dressing into it, slowly. It comes back every time.”
