Vinaigrettes & Emulsions

Understanding Emulsions Will Change How You Cook

An emulsion is a stable mixture of two liquids that normally do not mix — like oil and water. Understanding this one concept connects vinaigrettes, mayonnaise, hollandaise, pan sauces, and even the creamy pasta water sauce in cacio e pepe. Once you see the pattern, you see it everywhere.

The Science (Made Simple)

Oil and water repel each other. Left alone, they always separate — oil floats on top, water sinks to the bottom. To force them together, you need two things:

Mechanical energy — vigorous whisking breaks the oil into tiny droplets
An emulsifier — a molecule that grabs onto both oil and water, preventing the droplets from merging back together

The smaller the oil droplets, the more stable the emulsion. This is why an immersion blender makes a more stable mayonnaise than hand-whisking — it creates tinier, more uniform droplets.

Common Emulsifiers in Cooking

Emulsifier	Found In	How It Works
Lecithin	Egg yolks	A phospholipid with one water-loving end and one fat-loving end
Mustard mucilage	Dijon mustard	Seed-derived compounds that bridge oil and water
Starch	Flour (roux), pasta water	Starch granules absorb water and trap fat
Casein	Cream, cheese	Milk protein that stabilizes fat in water
Gelatin	Stock	Dissolved collagen that gives body and holds emulsions

This is why good stock makes better pan sauces (gelatin acts as an emulsifier), why pasta water makes cacio e pepe creamy (starch), and why Dijon mustard is in every vinaigrette (mucilage).

Classic Vinaigrette

The ratio: 3 parts oil : 1 part acid

This is the most fundamental dressing and the first emulsion you should master.

1/4 cup red wine vinegar (or sherry, champagne, lemon juice)
1 tsp Dijon mustard (the emulsifier)
1/2 cup extra-virgin olive oil
Salt, pepper

Whisk vinegar, mustard, salt, and pepper together first. Then slowly drizzle in oil while whisking constantly. The mustard holds it together.

Why vinaigrettes break (and how to fix them): A simple vinaigrette is a temporary emulsion — it will separate over time. To make it more stable: add more mustard, whisk more vigorously, add a tiny bit of honey (viscosity slows separation), or use an immersion blender.

Variations:

Shallot: Mince a shallot into the vinegar, let it macerate 10 min before whisking
Honey-lemon: Swap vinegar for lemon juice, add 1 tsp honey
Herb: Whisk in 2 tbsp minced fresh herbs at the end

Caesar Dressing

The classic emulsified dressing: garlic and anchovy mashed to a paste, egg yolk, lemon juice, Dijon, then oil drizzled in slowly. Finish with Parmesan. The anchovies provide umami depth without any fishy taste — most people cannot identify them in the finished dressing.

Aioli

Traditional aioli is garlic pounded with egg yolks and olive oil — essentially garlic mayonnaise. The immersion blender method has a near-100% success rate: place all ingredients in a tall, narrow container, insert the blender to the bottom, blend without moving for 15 seconds, then slowly pull upward. The emulsion forms from the bottom up.

Romesco Sauce

Roasted red peppers, toasted almonds, garlic, sherry vinegar, smoked paprika, blended with olive oil. A Spanish sauce that bridges the gap between a vinaigrette and a purée. Used in: Grilled Eggplant Sandwich (Ch.01), grilled vegetables, fish.

How Emulsions Connect Across the Curriculum

Once you understand emulsions, you see them everywhere:

Vinaigrette = oil + acid + mustard emulsifier
Mayonnaise/Aioli = oil + acid + egg yolk emulsifier
Hollandaise = butter + acid + egg yolk emulsifier (same as mayo, but warm)
Pan sauce = fond + liquid + butter emulsifier (monter au beurre)
Cacio e pepe = cheese fat + pasta water starch emulsifier
Cream sauce = stock + cream casein emulsifier

They are all the same principle applied in different ways.

Video Tutorials

Watch these to see the techniques in action.

How to Make a Vinaigrette — Ratio and Technique

The Science of Emulsions in Cooking

Homemade Mayonnaise — The Immersion Blender Method