An emulsion is just the fancy name for one liquid suspended in another liquid.
Oils do not dissolve in water but you can make them into an oil-in-water emulsion or a water-in-oil emulsion.
Emulsions make something thicker than either of the original parts. For example mayonnaise is an emulsion of sunflower oil and vinegar…and it’s thicker than either of those things.
Their physical properties are often more desirable and they can provide better texture, coating, ability and appearance, for example in salad dressings, ice creams, cosmetics and paints.
Usually the more oil you have in the emulsion, the thicker it is. For example with full fat milk you usually have about 3% oil, with single cream you have about 18%…this is what makes the second so much thicker. Whipped cream has air in it (this is actually part of the emulsion) which makes it so much fluffier.
Oil and water will just separate out if left alone – an emulsifier helps them to stay mixed.
Emulsifiers molecules have one part that is attracted to water and one part that is attracted to oil or fat. These have different names:
- Hydrophilic – the bit that is attracted to water molecules
- Hydrophobic – the bit that is attracted to oil molecules
When oil and water are shook up in the presence of an emulsifier the oil droplets get coated by the emulsifier. The hydrophilic bit faces outwards..and this repels other oil droplets and attracted water molecules. This means there is no separating out! The diagram below gives you a picture of what is going on.
However some people are allergic to emulsifiers (e.g. egg yolk is often used)