Foaming in stout beers

TL;DR

This paper reviews bubble formation in stout beers containing nitrogen and carbon dioxide, highlighting their unique properties, slow nucleation process, and potential as a model system for studying bubble nucleation, with implications for beverage technology.

Contribution

It provides a detailed analysis of bubble nucleation mechanisms in stout beers and proposes a novel approach for creating widgets using cellulose fiber coatings.

Findings

Bubble nucleation in stout beers is slow but follows the same mechanism as in carbonated drinks.

Stout beers serve as an accessible model for studying gas bubble nucleation.

A new widget design using cellulose fibers is suggested for improved foaming.

Abstract

We review the differences between bubble formation in champagne and other carbonated drinks, and stout beers which contain a mixture of dissolved nitrogen and carbon dioxide. The presence of dissolved nitrogen in stout beers gives them a number of properties of interest to connoisseurs and physicists. These remarkable properties come at a price: stout beers do not foam spontaneously and special technology, such as the widgets used in cans, is needed to promote foaming. Nevertheless the same mechanism, nucleation by gas pockets trapped in cellulose fibres, responsible for foaming in carbonated drinks is active in stout beers, but at an impractically slow rate. This gentle rate of bubble nucleation makes stout beers an excellent model system for the scientific investigation of the nucleation of gas bubbles. The equipment needed is very modest, putting such experiments within reach of undergraduate laboratories. Finally we consider the suggestion that a widget could be constructed by coating the inside of a beer can with cellulose fibres.