Falling Stout Bubbles Explainedfrom BBC News Online
Irish mathematicians may have solved the mystery of why bubbles in stout beers such as Guinness sink: it may simply be down to the glass. Simulations suggest an upward flow at the glass's centre and a downward flow at its edges in which the liquid carried the bubbles down with it.
But the reasons behind this flow pattern remained a mystery. Now a study on the Arxiv server reports simulations and experiments showing the standard glass' shape is responsible.
Many stout beers contain nitrogen as well as the carbon dioxide that is present in all beers. Because nitrogen is less likely to dissolve in liquid, that results in smaller and longer-lasting bubbles. But it is the sinking bubble that has confounded physicists and mathematicians alike for decades.
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