BEER GEEKS AND SCIENCE
IT’S AMAZING what can be accomplished in the course of drinking a few pints. While out at a tavern one night, a group of Spanish specialists in fluid mechanics found themselves bewildered by why beer in bottles foams up when the top of one bottle is tapped sharply by the base of another. “We all began to propose hypotheses and theories about the cause of the phenomenon, but none of them convinced us,” Javier Rodríguez, a professor at Universidad Carlos III de Madrid’s (UC3M) Department of Thermal and Fluids Engineering said. “So we decided to take it to the laboratory to do research using controlled experiments in well-defined conditions to analyze which physical phenomena are behind the appearance of that foam.” The findings were presented at the American Physics Society’s most recent conference on fluid mechanics. Using a special slow motion camera that records more than 5OOOO frames a second, the scientists broke down the phenomena into three distinct stages. Firstly, the bottle is hit and the compression waves travel down through the liquid, hitting the bottom and creating gas cavities or bubbles. These bubbles can’t take the pressure and begin to break down into even smaller pockets of gas, creating the foam. Finally, because this airy mixture weighs less than the liquid surrounding it, it begins to shoot up the neck of the bottle. “In fact,” said Rodríguez, putting a finer point on it, “those clouds of foam are very much like the mushroom cloud caused by a nuclear explosion.” This hydrodynamic affect is similar to boiling as far as the formation of bubbles, and the research could have serious applications in a number of areas, from creating longer lasting boat propellers (cavitation of this sort erode the blades over time) to predicting the behavior of gases in volcanic eruptions.