Emulsions and Suspensions

Oil and water do not mix — unless you cheat with chemistry. Mayonnaise is an emulsion: tiny oil droplets suspended in water, held stable by lecithin in egg yolk. The lecithin molecule has one end that loves water and another that loves oil.

Vinaigrette separates because it lacks a strong emulsifier. Mustard helps because it contains mucilage, a natural stabilizer. Milk is also an emulsion: fat globules suspended in water and stabilized by the milk fat globule membrane, a layer rich in phospholipids and membrane proteins. When milk curdles, the emulsion breaks.