Food emulsifiers have long been a vital ingredient in processed foods containing fats and oils, while more recently they've also been playing an important role in numerous low and no-fat products. The reason for this expansion is that, in addition to stabilizing water and oil mixtures, emulsifiers perform numerous other functions. These include functioning as aerating/foaming agents, defoaming agents, crystallization promoters, viscosity modifiers, dispersants, crystallization inhibitors, lubricants and agglomerating agents. No matter what the desired effect, understanding emulsifier functionality is critical to proper selection. Emulsion mechanics For the most part, water and oil emulsions either are oil-in-water (o/w) like milk, ice cream and mayonnaise, where oil is the dispersed phase and water the continuous phase; or water-in-oil (w/o) like margarine and butter, where water is the dispersed phase and oil the continuous phase. Emulsions aren't thermodynamically stable and can break in a variety of ways. The droplets can recombine or coalesce, ultimately returning to the original two separate phases. In other situations, the emulsion may undergo phase inversion. Here, the oil and water change places so an o/w emulsion becomes a w/o emulsion. A different form of emulsion instability is where the droplets retain their identities but become nonuniformly distributed in the container. This happens either through flocculation, where the droplets cluster together, or by creaming, where the density difference between the droplets and the continuous phase causes gravitational separation. Whatever the mechanism, emulsion instability can spell disaster in a food system.