The maths behind the bubbles in Guinness

Tuesday, 17 April, 2018

Beer and maths — an unlikely combo you may think, but when drinks giant Diageo wanted to know more about the strange behaviour of bubbles in a glass of Guinness the company turned to a mathematician. Professor William Lee from the University of Huddersfield specialises in industrial mathematics.

While Prof Lee was based at the University of Limerick he was asked to investigate the counter-intuitive behaviour of bubbles in a glass of Guinness — they sink rather than rise. After simulations and experiments, which he completed following a move to the University of Portsmouth, it was decided that the shape of the glass, with its sloping walls, was the determining factor.

“People think that the Guinness glass is designed to optimise the settling time,” said Professor Lee. “But now we have a better understanding of the theory behind it, we might be able to make an even better glass so that it settles faster. Unfortunately, the ideal shape would look like a giant cocktail glass!”

The Guinness bubbles research has created widespread media interest over recent years and earned lighthearted plaudits such as The Economist Babbage Award for Bizarre Boffinry. But it has also proved to be highly productive academically, resulting in a sequence of scientific articles. The latest is ‘Sinking Bubbles in Stout Beers’, published by the American Journal of Physics.

Industrial maths isn’t limited to beer — electrical goods conglomerate Philips approached Prof Lee in its quest for a perfect cup of filter machine coffee. The result was a mathematical model of coffee brewing that could be used to aid the design of machines. There were also significant findings about the processes by which coffee is extracted from beans.

This led to the co-authored 2016 article ‘Coffee extraction kinetics in a well-mixed system’, in the Journal of Mathematics in Industry. Now, Professor Lee is moving from filter coffee to espresso, investigating the link between strength and flavour.