14 DAY TRIAL // Besides a big belly, beer can mean pure science. And to get the best beer head, you must use mathematics.
New found formulas could explain why the foam of lager disappears in a moment, while a Guinness's sticks around. This mathematics applies not only for beer brewing, but in metallurgy, too.
The foam of a beer is made of a network of gas-filled bubbles with liquid walls, resulted from surface tension. The walls move constantly, with a velocity linked to the curvature of the bubbles; that's why the bubbles are constantly merging till the foam eventually disappears.
In 1952, the computer pioneer John von Neumann, developed an equation in two dimensions of the phenomenon, which has been now further improved in three, four, five and six dimensions by Robert MacPherson, from the Institute for Advanced Study in Princeton, New Jersey, and David Srolovitz, from Yeshiva University in New York.
"What happens in beer, is the small bubbles shrink, the big bubbles grow," said Srolovitz.
"Eventually, the big bubbles pop - although they pop for slightly different reasons. On Earth, there's gravity and the liquid that's within the walls tends to drain out back into the beer. The walls get thinner and thinner and eventually they pop."
"What this theory does is tells you how every single bubble in the froth will evolve. There are some materials properties that go into the final equation. So for beer, it will be the diffusivity of the gas in that little liquid layer that's in the wall of the bubble. Another is the surface tension."
Trying to explain the Guinness's foam persistence, Slobovitz said "I don't know the tricks that Guinness uses, they could be adding a little surfactant to get the head just right - that is just pure speculation on my part."
The foam's formulas could also be applied for other materials, too, like metals and ceramics, which are polycrystalline (they are made of many small crystalline grains kept apart by boundaries), in order to be improved. When heated, a metal piece will increase its volume. The small grains will be engulfed by the big ones that are growing, due to properties changes in the boundaries between grains.