Emulsions are liquid droplets that are mixed with another liquid. A vinaigrette dressing is an example of a oil-in-water emulsion as the oil droplets are mixed with water droplets. Emulsions are unstable because they tend to coalesce (clump together). Thus, a vinaigrette dressing will separate into an oil layer and a water layer after some time.
Milk proteins act as emulsifiers and stabilise oil-in-water emulsions by preventing fat droplets from coalescing. Emulsifiers are added to ice cream to actually reduce this stability meaning that the fat globules are more likely to partially coalesce when whipped in the ice cream machine.
Partial coalescence occurs when the milk fat globules from the cream cluster and clump together. This partial coalescence improves ice cream texture by preventing the air bubbles, which are whipped in by the ice cream machine, from breaking down.
Lecithin is a natural emulsifier found in egg yolk. If the emulsifier lecithin is not added to an ice cream mix, the fat globules will have the ability to resist partially coalescing. Consequently, the air bubbles will not be properly stabilised and the ice cream will not have the same smooth texture as one containing egg yolk.
However, if too much emulsifier is added, too much fat is de-emulsified and the coalesced fat droplets become so large that they are detectable on eating (C. Clarke, 2004). This is known as ‘buttering’.
Emulsifiers improve ice cream by:
- stabilising air bubbles, thus contributing to a smooth texture;
- promoting a continuos fat structure, thus contributing to a smooth texture;
- helping to produce a dry and stiff ice cream;
- preventing the ice cream from rapidly melting.
Clarke, C., The Science of Ice Cream 2004
Goff, University of Guelph Dairy Science and Technology, http://www.foodsci.uoguelph.ca/dairyedu/home.html
Marshall et al. Ice Cream, Sixth Editon, 2003