Emulsifier Definition - Emulsifying Agent

What an Emulsifier Is in Chemistry

Egg yolks are the emulsifier in mayonnaise.
Egg yolks are the emulsifier in mayonnaise. milanfoto / Getty Images

Emulsifier Definition

An emulsifier or emulsifying agent is a compound or substance at acts as a stabilizer for emulsions preventing liquids that ordinarily don't mix from separating. The word comes from the Latin word meaning "to milk", in reference to milk as an emulsion of water and fat. Another word for an emulsifier is an emulgent.

The term emulsifier may also refer to an apparatus that shakes or stirs ingredients to form an emulsion.

How an Emulsifier Works

An emulsifier keeps immiscible compounds from separating by increasing the kinetic stability of the mixture. Surfactants are one class of emulsifiers, which lower surface tension between liquids or between a solid and liquid. Surfactants keeps droplet size from getting large enough that components could separate based on density.

The method of emulsification matters in addition to the nature of the emulsifier. Proper integration of components extends the emulsion's ability to resist changes. For example, if you are making an emulsion for cooking, the mixture will maintain its properties longer if you use a blender than if you stir the ingredients by hand.

Emulsifier Examples

Egg yolks are used as an emulsifier in mayonnaise to keep the oil from separating out. The emulsifying agent is lecithin.

Mustard contains multiple chemicals in the mucilage around the seed that act together as emulsifiers.

Other examples of emulsifiers include sodium phosphates, sodium stearoyl lactylate, soy lecithin, Pickering stabilization, and DATEM (diacetyl tartaric acid ester of monoglyceride).

Homogenized milk, vinaigrettes, and metalworking cutting fluids are examples of common emulsions.