Mathematical Modelling of Bubble Nucleation in Stout Beers and Experimental Verification

Bubble nucleation is a phenomenon observed in many different physical situations from decompression sickness (DCS) to champagne research. It is of vital importance to the formation of a creamy head that is distinctive to stout beers. As stouts contain a lower quantity of dissolved carbon dioxide than other beers, nitrogen is also dissolved in the beer. This is necessary to produce the smaller bubbles required for a creamier head and the relatively lower quantity of dissolved carbon dioxide prevents the slightly sharp acidic taste present in other beers which contain more carbon dioxide. The problem with using less carbon dioxide is that the stout beers need to be initiated (the process of gas coming out of solution to form bubbles) as this does not happen as easily for other beverages which are solely carbonated. Canned stout beers are currently initiated using a device know as a widget. A widget is simply a hollow plastic sphere with a small hole in it. The widget initiates the stout by releasing a jet of gas into the liquid when the can is opened. Widgets, while effective, have a number of drawbacks including cost and the need for decontamination before it is placed in the sealed can. A cellulose fibre array is investigated as an alternative to the widget for canned stout beers. We demonstrate experimentally that these fibres can initiate the stout and develop a mathematical model to describe the growth of gas pockets within these fibres.