Bubble nucleation in stout beers

TL;DR

This paper extends a mathematical model to explain bubble nucleation in stout beers containing nitrogen and carbon dioxide, suggesting a potential alternative to widgets for head formation despite slower nucleation rates.

Contribution

It introduces a new model for bubble nucleation involving two gases in stout beers and proposes a coating of hollow fibres as a widget replacement.

Findings

Bubble nucleation in stout beers is slower but possible.

The extended model confirms bubble formation through observation.

Porous fibre coatings could replace widgets in cans.

Abstract

Bubble nucleation in weakly supersaturated solutions of carbon dioxide - such as champagne, sparkling wines and carbonated beers - is well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibres. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology (widgets) to release the bubbles which will form the head of the beer. We extend the mathematical model of bubble nucleation in carbonated liquids to the case of two gasses and show that this nucleation mechanism is active in stout beers, though substantially slower than in carbonated beers and confirm this by observation. A rough calculation suggests that despite the slowness of the process, applying a coating of hollow porous fibres to the inside of a can or bottle could be a potential replacement for widgets.