Why does mayonnaise stay mixed?
Mayonnaise contains tiny oil droplets dispersed in a watery phase. Substances in egg yolk help stabilize the droplets, slowing their tendency to merge and separate.
- The scientific idea
- Emulsion
- Fields of science
- Physics, Chemistry
How it works
Shake oil and vinegar and the sharp boundary between them briefly disappears. The oil has broken into droplets scattered through the watery vinegar. Leave the mixture standing and the liquids separate again. The oil never became a true solution in water.
Look closer
Mayonnaise keeps this droplet arrangement much longer. Mixing breaks the oil into small droplets, while emulsifying substances in egg yolk, including lecithin, help stabilize their boundaries with water. A spoonful can therefore look uniform even though it contains distinct oil and water regions. The contrast with sugar dissolved in tea is one of scale and structure: an emulsion contains droplets, while a sugar solution contains individually dispersed sugar molecules.