Kitchen Emulsions: Mayonnaise, Butter & Vinaigrette

Build a permanent oil-in-water emulsion, watch an unstable one separate, and break an emulsion apart into butter — all with an emulsifier’s help
Beginner🕐30 min●Low hazardcolloidsphysical-properties

Summary

Oil and water don’t mix — unless an emulsifier holds them together. In this edible experiment you’ll make three emulsions that behave completely differently: a permanent one (mayonnaise), a temporary one that separates as you watch (vinaigrette), and you’ll break an existing emulsion into butter. The difference comes down to how much emulsifier is present to keep oil droplets from merging — the same surfactant1 chemistry behind how soap cleans.

History

Emulsions are everywhere in food — milk, cream, butter, sauces — and cooks mastered them empirically long before the chemistry was understood. Mayonnaise (18th-century France) and the churned butter of countless cultures are two ends of the same phenomenon: one assembles an emulsion, the other tears one apart.

Hazards & preparation

Note

Entirely kitchen-safe; use raw egg yolk with normal food-hygiene care (or a pasteurised yolk). See the Safety page.

Part A — Mayonnaise: Build a Permanent Emulsion

Steps:

  1. Whisk together 1 egg yolk, 1 tbsp lemon juice or vinegar, 1 tsp mustard, and salt.
  2. Add ~200 mL neutral oil drop by drop while whisking constantly.
  3. After ~50 mL it thickens and you can add oil in a thin stream. Continue to a thick, creamy sauce.

The lecithin in the yolk (helped by the mustard) is the emulsifier. Add oil too fast, or use cold ingredients, and it “breaks” — restart with a fresh yolk and whisk the broken mixture back in slowly.

Part B — Vinaigrette: A Temporary Emulsion

Steps:

  1. Shake 3 tbsp olive oil, 1 tbsp vinegar, ½ tsp mustard, salt and pepper in a jar until cloudy and creamy.
  2. Set it down and time how long until it separates.
  3. Repeat without mustard and compare — the mustard’s mucilage slows separation but can’t stop it.

Part C — Butter: Break an Emulsion

Steps:

  1. Half-fill a jar with cold heavy cream (or use a mixer).
  2. Shake/beat: cream → whipped cream (3–5 min) → suddenly, butter grains and thin buttermilk (5–10 min).
  3. Pour off the buttermilk, rinse the butter in cold water until it runs clear, and knead in salt if you like.

What you should see

Mayonnaise thickens into a stable sauce that never separates; vinaigrette turns creamy and then splits back into layers within minutes; and cream passes through whipped cream before abruptly breaking into yellow butter and watery buttermilk. Three outcomes on one spectrum of emulsion stability.

Symptom Likely cause Fix
Mayo “breaks” (curdles/thins) Oil added too fast, or cold Restart on a fresh yolk; whisk broken mayo in slowly
Vinaigrette never emulsifies at all No emulsifier / too little shaking Add mustard; shake harder
Cream won’t turn to butter Too cold, or low-fat/ultra-pasteurised cream Warm slightly; use high-fat cream
Butter greasy / spoils fast Buttermilk not rinsed out Knead under cold water until clear

The Science

Oil and water are immiscible — mix them and the oil quickly coalesces back into a separate layer to minimise contact. An emulsifier is an amphiphile: one end is hydrophilic (water-loving), the other hydrophobic (oil-loving). It coats each tiny oil droplet — hydrophobic end into the oil, hydrophilic end out to the water — so the droplets can’t merge. That’s an emulsion.

The stability depends on how much emulsifier you have. Mayonnaise has abundant lecithin, so its droplets are fully coated and it lasts for weeks — a permanent emulsion. Vinaigrette has almost none, so its droplets recombine in minutes — a temporary emulsion. Butter is the reverse process: cream is an oil-in-water emulsion of fat droplets protected by membranes, and agitation smashes those membranes so the fat coalesces and separates out — breaking the emulsion.

Questions to Explore

  1. Why does mayonnaise last for weeks but vinaigrette separates in minutes?

    Hint / answer

    Mayonnaise has plenty of emulsifier (yolk lecithin) to fully coat every oil droplet, so they can’t merge. Vinaigrette has essentially none, so droplets recombine and the layers separate almost at once.

  2. Why must you add the oil to mayonnaise slowly at first?

    Hint / answer

    Early on there’s little emulsifier surface available; adding oil slowly keeps droplets small and fully coated. Dump it in and the droplets are too big to stabilise, so the emulsion breaks.

  3. Making butter is the opposite of making mayonnaise — how?

    Hint / answer

    Mayonnaise assembles an oil-in-water emulsion with an emulsifier’s help. Churning butter destroys cream’s emulsion by breaking the membranes around the fat globules so the fat coalesces and separates from the water.

Going further

Footnotes

  1. Colloid — A mixture in which very small particles are dispersed through another substance without dissolving.↩︎