Foam physics: calculating the perfect pour for beer

From creating drinks with distinctive looks to providing aromas for connoisseurs, beer foam is big business. The complex interplay between the components of a beer, the vessel from which it’s poured and the glass it’s poured into has garnered plenty of attention from researchers, brewers and drinkers. Now a new study looks to provide predictions about how a beer will foam.

Researchers analysed brewing with numerical simulations to determine foam patterns, heights, stability, beer/foam ratio and foam volume fractions. The findings have been published in Physics of Fluids, by AIP Publishing.

The frothy foam on top of beer is an important characteristic for beer drinkers across the globe. It’s basically produced by bubbles of gas, predominantly carbon dioxide, rising to the surface. The chemical components that produce the head are wort protein, yeast and hop residue.

To achieve an accurate prediction of beer foam formation and collapse is challenging because complex numerical models are required to account for all its nonlinear beer foam effects, such as lacing (glass adhesion or cling), whiteness, creaminess and strength.

The computational approach used in the study is called a multiphase solver to tackle beer heads.

“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,” said author Wenjing Lyu. “By using a multiphase solver, it is possible to accurately predict the behaviour of the system and optimise 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.”

To tackle this task, the group partnered with Einstein 1, a startup developing a new bottom-up tapping system in which the nozzle pushes up a movable magnet on the bottom of a glass to create a temporary inlet. As the glass fills, the magnet moves back into place and the beverage is ready to drink. After repeatability studies to establish stable pouring conditions, they assembled a model that was then validated with experiments.

The group found that foam from Einstein 1’s tapping system is generated only in the first moments of pouring. Higher temperatures and pressures yielded more foam.

After that, beer’s liquid phase kicked in. Determined in large part by bubble size, the beer’s foam phase slowly decayed, taking approximately 25 times longer to fully fizzle out than it took the foam to form.

Alongside further optimising their computational approaches, the group next looks to study the effects of nozzle shapes.

“This will help in controlling foam formation, reducing consumption and pouring time, and improving the overall efficiency of the pouring process,” Lyu said. “By accurately simulating the foaming process, our model can help to improve the quality of the final product, reduce costs and increase productivity in industries such as food and beverage, chemical and others.”

Top image credit: iStock.com/dan_prat