Some liquids refuse to combine without help. For example, water and oil will temporarily integrate through colloidal suspension if forced, but their physical nature compels them to separate when that force is removed. Emulsifiers can intervene in this situation. With their help, you can suspend a fine dispersion of the first liquid in the second, insoluble, immiscible liquid – and keep it there. This blend is known as an emulsion.
Molecules that act as emulsifiers contain one hydrophilic end (which accommodates water) and one hydrophobic end (which accommodates oil). Each end associates the liquid it prefers and repels the other. If you stack enough of these molecules together, you create droplets of one liquid that remain suspended within the other.
In addition to an emulsifier, emulsions require force. In cooking, this force typically comes in the form of whisking or blending. The force breaks apart the added liquid so that it can disperse and form droplets. Then, the emulsifier prevents the two liquids from separating. A stable emulsion contains droplets that are small enough to remain in suspension and evenly distributed throughout the mixture. The viscosity, ratio of emulsifier to mixture, and any additives will affect the emulsion’s stability as well.
Eggs make excellent emulsifiers, because they contain the fatty substance lecithin. Found in the yolk of the egg, lecithin is a mixture of phospholipids, like phosphatidyl choline and phosphatidylethanolamine. The best-known example of an egg emulsifiers is mayonnaise, where oil droplets are suspended in a water/vinegar mixture. In addition to its emulsifying properties, lecithin can act as a preservative and moisturizer. It is critical for neurological health and supports the function of the nervous system, heart, liver, and kidney.
Both dried eggs and fresh eggs have emulsifying properties. Sometimes egg yolks are added to whole egg blends in order to increase their emulsifying abilities.
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