Imagine you're sitting in a pub with a pint of real ale. Gravity keeps the beer in the glass and the bubbles rise through it. Now imagine that you have a globule of beer floating in a spacecraft in zero gravity. What happens to the bubbles? What direction do they move in--if they move at all? Are they the same size as on Earth? Would the beer have a frothy head? Are there likely to be any other unusual effects?

In microgravity (zero gravity), surface tension tends to be the driving force behind fluid behaviour. Once released from whatever container it was in, your blob of beer would just float there. However, if you opened a can of beer in orbit, you'd create a nifty little beer cannon that cover the wall with several globs of beer.

Bubbles would still form in your beer globule, because the carbon dioxide would still come out of solution under room temperature and pressure, but they wouldn't move in any direction. Not only that, but the larger bubbles (and head) in Earth beer form because the bubbles float to the top of the glass and bump into each other on the way. Space beer would have a number of bubbles throughout, so you'd just get a foamy mass. Bubbles are likely to be fewer and larger in microgravity because as they form, they remain at the nucleation sites instead of drifting off. However, their growth may be slower because it would depend more on diffusion through the liquid and less on circulation. On Earth, the behaviour of beer depends largely on gravity. In free fall, surface tension, momentum, vapor pressure and diffusion dominate, so small bubbles are less likely to meet and fuse, but big bubbles are less likely to reach the surface and burst.

Forces hardly noticeable on Earth have weird effects in microgravity and complicate working in space. Localised drying and the lack of convection cause differences in viscosity, vapour pressure and surface tension, which make fluids creep, drift and distort unexpectedly.

Astronauts aren't allowed to drink carbonated drinks in orbit, because the body relies on gravity to burp excess gas. No beer is one of the many sacrifices one must make for space exploration.

Source: Edited from the responses of Todd Dark-Fox and Jon Richfeild in the NewScientist.