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Draft Theory

A mystery that has haunted pubs and frustrated drinkers for years may soon be solved by scientists at Imperial College of Science, Technology and Medicine. Neil Hepworth, a PhD student in the Department of Chemical Engineering and Chemical Technology, is working on a project, funded by Brewing Research International and the Biotechnology and Biological Sciences Research Council, which could lead to the formula for pouring the perfect pint of beer.

Neil Hepworth is looking at the factors that determine how long it takes a pint to settle. When some types of kegged beer are poured stable microbubbles develop which can give the beer an unpleasant cloudy appearance and can be unappealing to the consumer. Neil Hepworth explains, "There is a general lack of understanding of the gas-liquid dispersion characteristics during beer dispense and the challenge is to understand why bubble haze is formed and to predict its presence or absence."

Certain types of beer are delivered from the keg to the tap using a pressurized gas mixture of nitrogen and carbon dioxide. Previous research has shown that it is the presence of dissolved nitrogen gas that can lead to the formation of unappealing microbubbles. (see notes to editor 2)

"The gas composition seems not to be the major factor affecting haze duration. The major factors seem to be those that affect the rate of bubble creation which are things such as liquid flow rate into the glass and the use of a sparkler, which is a restriction in the beer tap to used to create bubbles." explains Neil Hepworth.

Commenting on his progress Neil Hepworth explains, "In the brewing industry methods to control the phenomenon of bubble haze are empirical and thus the solutions are very case specific. I am trying to explain the phenomenon using the fundamental scientific principals behind it. I wish to understand why microbubbles form and use this information to formulate a model that will allow us to predict what a bubble haze will do in any given conditions."

The research is being conducted using a purpose built laboratory scale beer dispensing system and a consistent synthetic beer that mimics the physical properties of a commercial beer. Experimental analysis of bubble behaviour has enabled Mr Hepworth to characterise the bubble haze and take the first steps in constructing a model. He explains, "The initial modelling is for the simplest case of predicting the time it takes for a single bubble to reach the top of the glass. It takes into account initial bubble size, levels of dissolved gas in the liquid and the rate at which the bubble grows from gas entering the bubble from the solution. The model will eventually be developed to account for multiple interacting bubbles, bubble creation and liquid motion."

For Further Information contact:

Judith Moore
Press Office
Imperial College
Tel: +44 (0) 20 7594 6702

Notes to editors:

1. Neil Hepworth is currently working on a PhD projected entitled Bubble Stability in Beer Supervised by Dr Julie Varley in the Department of Chemical Engineering and Chemical Technology. Department website at:

2. Gas pressure can be used to deliver beer from the keg to taps. Traditionally carbon dioxide was used. To create a creamy foam for beers such as ale, stout, and porter, a mixture of carbon dioxide and nitrogen is now sometimes used. Although nitrogen is 60 times less soluble in water than carbon dioxide some nitrogen still becomes dissolved in the liquid and as a result stable microbubbles form on dispense.

3. Imperial College of Science, Technology and Medicine is an independent constituent part of the University oUniversity of London. Founded in 1907, the College teaches a full range of science, engineering, medical and management disciplines at the highest level. The College is the largest applied science and technology university institution in the UK, with one of the largest annual turnovers (UKP330 million in 1998-99) and research incomes (UKP173million in 1998-99). Web site at