Published online 8 March 2011 | Nature | doi:10.1038/news.2011.140

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The widget-free way to foamy stout

Fibrous coatings inside cans of stout could replace the froth-creating plastic spheres.

Dissolved nitrogen gives stout a long-lasting head and creamy mouth feel.J. Lee/Photolibrary

When pouring a can of stout such as Guinness, the physics behind the satisfying head of beery foam that forms is probably the last thing on most people's minds.

A new study, published in the online physics archive arXiv1, investigates the phenomenon in depth, and suggests a new technique for bubble creation that could supersede the 'widget' — a hollow plastic sphere with a small hole in it — currently used to set some canned beers foaming when opened.

Stouts bubble less readily than lagers or other carbonated drinks when poured because they contain dissolved nitrogen as well as the carbon dioxide that drives the fizz. Adding nitrogen makes the beer less acidic, and gives a longer-lasting head with relatively small bubbles that are behind stouts' smooth, creamy 'mouth feel'.

But the addition also demands the use of the widget, which takes in gas and beer as it floats in the canned stout and, when the can is opened and the pressure drops, jets it out again through the hole, helping to create the foam.

The new study suggests that the same result could be achieved by coating part of the can's interior with cellulose fibres.

"It would be a much simpler process than using widgets," says William Lee, a physicist at the Mathematics Applications Consortium for Science and Industry at the University of Limerick, Ireland, who led the work.

A fibrous coating might be cheaper and more environmentally friendly than the current practice of injecting liquid nitrogen into cans to pressurize the widget, he says.

Suddenly ahead

In carbonated drinks that do not contain dissolved nitrogen, the head forms spontaneously when the gassy liquid is poured and hits tiny fibres of cellulose — essentially dirt — on the surface of the glass. When the liquid hits these fibres, pockets of gas are created that allow a froth of carbon dioxide bubbles to form. This is the principle behind foaming in champagne, fizzy soft drinks and lagers.

"We thought this process didn't work at all in stout because when you pour it without a widget it looks completely flat," says Lee, "so we decided to investigate why it didn't."

Lee and his colleagues developed a mathematical model of bubble formation from cellulose fibres in liquids containing both carbon dioxide and nitrogen.

"Our model suggested that stout should in fact produce bubbles," he says, "and when we poured some onto some cellulose fibres and looked closely there were bubbles everywhere."

However, stout bubbles are generated about 20 times as slowly as those in carbonated drinks, which is why the beer does not seem to foam.

Using their model, the researchers calculated that including a 2.9-centimetre square of fibrous material within the can would form enough bubbles to create the desired head of froth if the stout was poured slowly, removing the need for widgets.

Bubble and tweak

"Their mathematical model is quite simplistic, which is appealing," says Michael Chappell, a biomedical engineer at the University of Oxford, UK, who helped develop a similar model for champagne2. "You could tweak the carbon dioxide and nitrogen concentrations to control the rate at which the bubbles form."

However, he adds, the bubbles might fill with liquid while the can was in storage. Lee says the coating would be placed in the gap at the top of the can: "It would be ok as long as the cans weren't stored upside-down."

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Andrew Alexander, a chemical physicist at the University of Edinburgh, UK, also believes that can coatings would be impractical compared with widgets. "Widgets are genius — they're cheap, work really well, are totally non-toxic and don't mess with the beer," he says. "Would a fibrous coating be cheaper than what is essentially a ping-pong ball with a hole in it? I don't think so."

But Lee says that using widgets slows down the process of canning stout. "Oxygen stuck in the widget can affect the beer's flavour, so you have to pump nitrogen in several times to remove it," he says. "The cellulose coating is an alternative worth investigating."

However, it is likely to be some time before fibre-lined stout cans appear on supermarket shelves. "We've spoken to brewers," says Lee, "but we're not sure if they're interested yet." 

  • References

    1. Lee, W. T., McKechnie, J. S. & Devereux, M. et al. arXiv:1103.0508v1 (2011).
    2. Uzel, S., Chappell, M. A. & Payne, S. J. et al. J. Phys. Chem. B 110, 7579-7586 (2006).

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  • #61761

    I believe you mean 60ft. Where your much more likely to take an O2 hit.

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