Why emulsions hold together, and why they break
Intermediate Kitchen science
Why emulsions hold together, and why they break is an emulsion is tiny droplets of one liquid suspended in another that normally will not mix, like oil in vinegar or butter in water.
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How do you do it?
- Add the oil slowly at first, a few drops at a time, until the mixture thickens; then you can pour faster.
- Include an emulsifier: mustard, egg yolk, honey, garlic paste or a spoonful of mayonnaise all help droplets stay apart.
- Keep warm butter sauces like hollandaise warm, not hot, and serve them within an hour; overheated, they split.
- To rescue a broken sauce, whisk a fresh yolk or a teaspoon of water in a clean bowl, then drizzle the broken sauce back in.
Why does it work?
Oil and water repel each other, so droplets of oil keep finding each other and merging until they float as a separate layer. Whisking breaks the oil into tiny droplets, and an emulsifier keeps them apart. Emulsifiers like the lecithin in egg yolk have one end that likes water and one that likes fat, so they wrap each droplet in a protective coat. A thicker surrounding liquid also slows droplets from meeting. Emulsions break when there is too much oil for the water and emulsifier to hold, when oil goes in too fast, or when heat makes egg proteins clump or butter fat melt out.
What are the common mistakes?
- Pouring all the oil in at once — droplets are too big to stay suspended.
- Letting a butter sauce boil — fat separates into a greasy pool.
Still stuck? Watch someone do it on YouTube.
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