Confectionery: Creating food structure out of thin air!

Figure 1: A selection of commercially available bubble containing products

Incorporating bubbles can be challenging in any food system, simply because gas is three orders of magnitude less dense than the food matrix into which it is added, and inevitably, the dispersion is unstable. It is even more challenging to create the right bubble-containing structure that will give the product the mouth-feel that its consumer desires. In addition to the food matrix, a bubble containing structure is typically characterised firstly by the fractional volume of the product occupied by bubbles and secondly, the bubble size distribution. Thus, ingredient formulation as well as the processing technique employed have to work in tandem in order to result in a product that is desirable and stable over its shelf life. In terms of product formulation, it is imperative to have agents in the ingredient mix which exhibit what is commonly known as gas-liquid interfacial activity. Such agents normally hold the bubbles within the matrix and stabilise the dispersion by lowering interfacial energy. In practice, however, a number of components in a product formulation will possess interfacial activity, and it can be extremely complex to analyse which component or components have succeeded in migrating to the interface and in what proportions.

Techniques such as confocal laser scanning microscopy are only just being applied to unravel such phenomena. The technology employed to incorporate bubbles into food systems is also equally important, if not more. A variety of methods are used commercially, but the most common method involves admitting the food system at a temperature where it is predominantly in the fluid state, together with a gas (not necessarily air), into a mixing head maintained under a positive pressure and driven by an impeller. The dispersion formed is then drawn out and restored to atmospheric pressure, with the temperature adjusted to a value that is needed for further processing of the dispersion (Figure 2).