The yolks inside of eggs are natural emulsifiers. Emulsifiers are used to stabilize and blend two substances that are normally unmixable together. Emulsifiers also enhance the uniformity and appearance of a mixture. A good example of an emulsion is an oil and water mixture.
Egg yolk has a high concentration of water, lecithin, lipoproteins, cholesterol and phospholipids. The cholesterol portion of egg yolk stabilizes water and oil mixtures. According to Encyclopædia Britannica, the emulsifying properties of egg yolk are not affected by hot and cold temperatures. The cholesterol content of egg yolks declines with age, while the cholesterol content remains the same.