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🥄 Emulsions: mayonnaise, hollandaise and the physics of not splitting

Oil and water do not stay mixed. Mayonnaise and hollandaise are what happens when you hire the right molecule, and what happens when you don't.

5
lessons
~20 min
to learn
🔬 Science
subject
Adults
level
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What you’ll learn

  1. Two liquids that refuseSee an emulsion as one liquid dispersed in another, and classify kitchen sauces as oil-in-water or water-in-oil.Oil and water minimise their shared surface because that interface costs energy. Shake them and you only buy seconds unless something pays the tax. Which liquid is the ocean decides whether you have cream or butter.
  2. The molecule that sits on the fenceExplain how phospholipids and yolk proteins lower interfacial tension and block coalescence.Amphiphiles coat oil droplets. Mustard helps a little. Yolk proteins can thicken as well as coat, which is why heat is both a tool and a threat.
  3. Mayonnaise, packed until it standsConnect McGee’s droplet count and oil fraction to the slow-oil method, and treat the Mahón story as a story.Finished mayonnaise can be eighty percent oil by volume. The coats have to arrive as fast as the new surface. The name-fight is documented; the 1756 siege recipe is not.
  4. Hollandaise, the same physics on a stoveHold McGee’s rule: thicken yolks without coagulating them, and know what whole butter’s water is doing.Same oil-in-water yolk emulsion, now warm. Below the window it is soup. Above it, curds and grease. Whole butter thins as it enriches; clarified butter only thickens.
  5. Splitting, and stealing it backName coalescence as the failure, and practise restarting a water phase instead of throwing the bowl out.Stop adding fat. Start a new ocean — water or a fresh yolk — and whisk the wreck in as if it were oil. Béarnaise is the same physics with tarragon in the water.

Questions this course answers

Mayonnaise and hollandaise are which kind of emulsion?

Both sauces are oil-in-water. The continuous phase is watery (yolk water, lemon, vinegar). The dispersed phase is oil or butterfat. Butter is the other way round.

Put these mayonnaise steps in the order the physics actually requires

Emulsifier has to be in the water first. Oil last and slow. Rescue is the same method run on the broken bowl.

Match each kitchen thing to the job it actually does

Amphiphiles and proteins guard the interface. A whisk only makes droplets. Without a coat those droplets merge.

When mayonnaise is finished, roughly what percentage of its volume can be occupied by oil droplets?

McGee: as much as 80 percent of the finished volume is oil droplets. That packing is why mayo stands instead of pouring.

In your own words, why can the same egg yolk that holds mayonnaise for days lose a hollandaise in a minute of extra heat?

McGee: thicken the yolks without coagulating them. Barham: yolk proteins start to thicken above about 58 °C. The useful band is narrow. Cold mayo never enters it.

Name the phospholipid emulsifier egg yolk is famous for.

Lecithin is the yolk phospholipid the Exploratorium and food-emulsifier texts name. Proteins help. Gluten, pectin and collagen are other food networks, not this coat.

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