Emulsions
Vegetable oils do not dissolve in water. If oil and water are shaken together, tiny droplets of one liquid spread through the other liquid, forming a mixture called an emulsion. Emulsions are thicker than the oil or water they contain. This makes them useful in foods such as salad dressings and ice cream. Emulsions are also used in cosmetics and paints.
Emulsifiers
If an emulsion is left to stand, eventually a layer of oil will form on the surface of the water. Emulsifiers are substances that stabilise emulsions, stopping them separating out. Egg yolk contains a natural emulsifier. Mayonnaise is a stable emulsion of vegetable oil and vinegar with egg yolk. Emulsifier molecules have two different ends:
- A hydrophilic (water-loving) ‘head’ that forms chemical bonds with water but not with oils
- A hydrophobic (water-hating) ‘tail’ that forms chemical bonds with oils but not with water