I live in the southern England, where the perfect head of beer is absolutely no head at all. So it’s always a shock to travel elsewhere and be served a glass of beer with a tall, frothy head. A good head is apparently a sign of quality in beer, so people who make and serve the stuff (outside of England) are keen to get the head just right.

Now, physicists in South Korea and Germany have done an experimental and numerical study of beer foam that could help barkeepers to rapidly pour a glass from the bottom-up, while ensuring that the desired amount of foam is created.

If you are wondering what bottom-up pouring is, I can tell you because I just had the pleasure of seeing it in action in a Japanese restaurant in London. The beer is served in a cup with a hole in the bottom that is surrounded by a magnet. Beer is pumped into the hole and when the cup is full, a magnetic disk seals the hole. The result is a rapid fill and a beer with absolutely no head – or at least that’s how it was served in London.

Multiphase solver

The study is claimed to be the first investigation of beer froth using a multiphase solver, as team member Wenjing Lyu explains. “Simulation of a bottom-up pouring process using a multiphase solver is a complex task that involves modelling the physical and chemical interactions that occur during the process, such as fluid dynamics, heat and mass transfer, and chemical reactions”.

Lyu adds “By using a multiphase solver, it is possible to accurately predict the behaviour of the system and optimize the design of the nozzle outlets and the cup geometry to ensure the fastest possible bottom-up pouring under various conditions such as pressure, temperature, and carbonation”.

While the researchers were focused on filling speed, I hope that the work will allow users of bottom-up systems to achieve the perfect head of beer for their customers. While punters in London seemed very happy with a zero foam pint, I don’t think that the German members of the team – some of whom are from Bavaria – would be happy to drink a foamless stein of beer during Oktoberfest.

The researchers describe their study in AIP Physics of Fluids.

Spiky structures

Sticking with the physics of fluids, have you ever wondered why icicles tend to have a rippled shape, with alternating ridges and valleys running down the length of the spiky structures? This mystery has puzzled physicists for centuries, and now the answer may have been found by Menno Demmenie and colleagues of the Institute of Physics and the Van ’t Hoff Institute for Molecular Sciences at the University of Amsterdam.

The team built an icicle machine in which water is trickled in sub-zero temperatures. The team then first determined the ideal flow rate of water required to create an icicle. If the water comes too fast, it just drips onto the floor, and if it comes too slowly, the icicle grows up rather than down.

By changing the salt content of the water and using colouring to monitor flow, the team came up with an explanation for why ripples form. When pure water was used, few ripples were seen and the icicles resembled candles. However, with salty water, the salt gets pushed out of the bulk ice and onto the surface of the icicle. This creates a film of salty water that flows along the surface of the icicle, forming the rippled structures.

The research is described in Physical Review Applied.

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