Foam might seem like the most fleeting part of a beer, but it turns out to be governed by surprisingly intricate physics. A seven-year study from ETH Zurich maps out the mechanisms that help certain brews hold a thick, creamy head while others collapse almost immediately – and shows that different beer styles rely on entirely different stabilizing forces.
Using a suite of interfacial analysis tools, including surface rheometry, tensiometry, dynamic thin-film balance experiments, and proteomics, the team dissected how bubble films form, drain, and rupture in ales and lagers. Their measurements, detailed in Physics of Fluids, show that lager foams are propped up primarily by surface viscoelasticity: proteins from barley malt accumulate at the air–beer interface, forming a mechanically resilient layer that slows drainage. Belgian Tripel beers, however, follow another playbook. With minimal measurable surface viscosity, their stability comes instead from Marangoni stresses – flows driven by surface-tension gradients that continually recirculate liquid around each bubble.
These distinctions explain why higher-fermentation Belgian ales–Tripels and Dubbels–often outperform lighter Singel styles and many lagers. Proteomic data from the study revealed that lipid transfer protein 1 (LTP1), long suspected to influence foam, appears in greater abundance and with different modifications in more intensely fermented beers, contributing to their distinctive interfacial behavior.
The findings have already drawn industrial interest. As lead researcher Jan Vermant noted in a press release, “We now know the precise physical mechanism and are able to help the brewery improve the foam on their beers,” adding that foam isn’t universally valued – “it’s a cultural thing.” The same physics reaches far beyond brewing: the team is collaborating with partners including Shell to understand foam in lubricants, and with food scientists to explore protein-based stabilization in milk foams.
The work provides a potential blueprint for engineering foams in beverages and other multicomponent mixtures – from industrial lubricants to culinary emulsions.
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