This is how a beer is optimally tapped

Especially in the Rhenish strongholds of the carnival, countless beers are being tapped these days - from professional dispensing systems, but also from many smaller party kegs with five or ten liters content.

Anyone who has ever tapped beer from one of these kegs knows the problem: sometimes the glass fills up almost entirely with foam and you have to wait patiently until it has turned back to beer before you can top up. And then the game repeats itself and it can take minutes to hold a glass with an acceptable fill level and not too much foam. But the opposite problem also occurs. Sometimes a glass fills up quickly, but is not crowned with a white flower.

The hobby tapper learns over time how the processes and results can be improved - first hold the glass at an angle, place the tap on the inner wall and initially not select the flow rate too high. One certainly cannot speak of an optimization in the scientific sense, but that is not the point in this case.

From the professional perspective of an innkeeper, the optimal tapping is nevertheless of great importance. On the one hand, the guest should of course be served a “perfect” beer with a nice head of foam – not too small and not too big.

And so scientists led by Wenjing Lyu from the Chinese Academy of Sciences have investigated the question of how beer tapping can be optimized. They have now published their findings, which they gained with the help of computer simulations, in the journal "Physics of Fluids".

"These model calculations are a complex task because numerous physical and chemical interactions that occur when beer is poured have to be taken into account," says Lyu. "It's about fluid mechanics, the transfer of heat and masses and also chemical reactions."

In addition, the whole thing also depends on the temperature of the beer, the pressure, the carbon dioxide concentration and the shape of the tap tip. Never before have researchers simulated this extremely complicated process on the computer.

The researchers report that their model allows them to predict the properties of the beer crown - its height, stability and the volume ratio of liquid beer and foam in the glass.

The research results cannot be implemented immediately for the hobby tapper. However, the findings can be used to optimally design taps - optimal in the sense that the greatest possible flow rate is achieved, with which a perfectly crowned beer can still be produced. In short: the new findings allow as many beers as possible to be tapped per unit of time.

And this is where the economic relevance of the research work becomes clear. The scientists have a cooperation with the startup "Einstein 1", which is developing new types of taps.

"Aha! Ten minutes of everyday knowledge" is WELT's knowledge podcast. Every Tuesday and Thursday we answer everyday questions from the field of science. Subscribe to the podcast on Spotify, Apple Podcasts, Deezer, Amazon Music, among others, or directly via RSS feed.