You can't just change one thing and get it right.
For seven years, researchers at ETH Zurich pursued a question that began with a brewer's offhand remark, and in doing so uncovered something deeper than a recipe: that the humble head on a glass of beer is a theater of competing physical forces, each beer style maintaining its foam through its own distinct logic. Published in Physics of Fluids, the findings reveal that lagers rely on protein-stiffened bubble walls while Belgian Tripels harness the invisible currents of Marangoni stresses—surface tension variations that move like tides across a liquid's face. What began as curiosity about fermentation has opened into a broader understanding of foam itself, with implications reaching from electric vehicle safety to the design of greener industrial chemicals.
- Decades of brewing science rested on a single assumption—that proteins alone hold beer foam together—and that assumption has now been overturned.
- Different beer styles, it turns out, are running entirely different physical playbooks: lagers stiffen their bubble walls with protein films while Belgian Tripels surf invisible surface-tension currents to stay alive.
- The complexity cuts both ways—brewers cannot simply dial up one ingredient to fix their foam, because improving one mechanism can silently sabotage another.
- ETH Zurich has partnered with one of the world's largest breweries to translate seven years of physics into practical improvements at industrial scale.
- The science is already migrating outward—into foaming lubricants inside electric vehicles, fluorine-free surfactants, milk foam stability, and even foam systems designed to carry bacteria for medical use.
A Belgian brewer once told Jan Vermant that he controlled his brewing process by watching the foam. That passing remark became the seed for seven years of research at ETH Zurich, culminating in findings that overturn long-held assumptions about what keeps beer foam alive.
Vermant's team, publishing in Physics of Fluids, examined foam stability across multiple beer styles and found that different beers maintain their heads through entirely different physical mechanisms. In lagers, stability comes from surface viscoelasticity—the stiffness of protein films surrounding each bubble. More protein means a stiffer shell and a longer-lasting head. Belgian Tripel beers, however, barely use this mechanism at all. Instead, they rely on Marangoni stresses: forces generated when variations in surface tension create movement across a liquid's surface, much like soap dropped onto water sends floating leaves rushing outward. Those same invisible currents help hold the bubbles in place.
The differences run deeper still. In Singel beers, proteins pack tightly across bubble surfaces like a two-dimensional suspension. Dubbel beers form a mesh-like membrane. Tripel beers behave more like simple surfactants. One protein, LTP1, appears central to these distinctions, though the full picture remains incomplete.
What makes the findings practically significant is their warning about non-linearity. Adding more of a single ingredient won't reliably improve foam—it may even destabilize it by disrupting a mechanism the brewer didn't know was operating. The ETH team has partnered with one of the world's largest breweries to apply these insights carefully, working on mechanisms one at a time.
The reach of the research extends well beyond the glass. Vermant's group is now working with Shell to address dangerous foaming in electric vehicle lubricants, developing fluorine-free industrial surfactants, and studying milk foam stability with food researcher Peter Fischer. A brewer's casual observation has become a doorway into foam physics with consequences across industries.
A Belgian brewer once gave Jan Vermant a simple answer to a simple question. When asked how he controlled the brewing process, the brewer said: by watching the foam. That offhand remark became the seed for seven years of investigation at ETH Zurich, a period of sustained scientific curiosity that has now yielded something brewers have sought for generations—a genuine understanding of what makes beer foam last.
Vermant, a professor of soft materials at the university, led a team that examined the physics of foam stability across different beer styles, publishing their findings in Physics of Fluids. What they discovered overturned decades of assumption. For years, scientists had believed that beer foam remained intact primarily because proteins from barley malt formed protective layers around each bubble, controlling how the bubble surface flowed and how it held tension. The new work shows the reality is far messier and more interesting than that. Different beers, it turns out, keep their foam alive through entirely different physical mechanisms.
When the researchers analyzed Belgian ales—Tripel, Dubbel, and Singel varieties—a clear pattern emerged. Tripel beers produced the most stable foam, followed by Dubbel, while Singel beers, with their milder fermentation and lower alcohol content, held the weakest head. But the mechanism differed dramatically between them. In lager beers, foam stability depends on what physicists call surface viscoelasticity: the stiffness of the protein film surrounding each bubble. More protein means a stiffer film, which means longer-lasting foam. Tripel beers, by contrast, barely rely on this mechanism at all. Instead, they maintain their foam through Marangoni stresses—forces that arise when variations in surface tension create movement across a liquid's surface. Imagine crushed tea leaves floating evenly on water. Drop soap onto the surface and the leaves suddenly rush outward, pulled by invisible currents. Those same currents, persisting in the beer, help stabilize the bubbles.
The researchers found that the protein-rich shells surrounding each bubble behave differently depending on the beer. In Singel beers, the proteins pack tightly like small spheres across the bubble surface, resembling a two-dimensional suspension. Dubbel beers show a mesh-like membrane that strengthens bubbles further. Tripel beers again stand apart, with bubble dynamics that resemble simple surfactants—the molecules used to stabilize everyday foams. One protein in particular, LTP1 (lipid transfer protein 1), appears to play a central role, though the precise reasons for these differences remain incompletely understood.
What makes this work genuinely useful is what it reveals about the non-linearity of foam stability. Vermant emphasizes that you cannot simply add more of one ingredient and expect improvement. Adding more surfactants to increase viscosity might actually destabilize the foam by interfering with Marangoni effects. The key is understanding how multiple mechanisms interact and working on them one at a time, not several simultaneously. Nature, he notes, does this instinctively through fermentation and ingredient selection. The ETH team has partnered with one of the world's largest breweries to apply these insights, moving from pure science toward practical improvement.
The implications extend far beyond the brewery. In electric vehicles, lubricants can begin to foam, creating serious safety risks. Vermant's group is now collaborating with Shell to understand how to break down these foams efficiently. The team is also developing environmentally friendly surfactants that do not rely on fluorine or silicon—a direction Vermant sees as important for industrial and environmental reasons. In collaboration with food researcher Peter Fischer, they are studying how proteins stabilize milk foam. The knowledge extracted from beer, it turns out, has applications in lubricants, food science, and even in designing foams that could carry bacterial systems for medical or industrial use. A brewer's casual observation about watching the foam has become a doorway into understanding a physical phenomenon with consequences far beyond the glass.
Notable Quotes
By watching the foam.— Belgian brewer, answering how he controlled the brewing process
The stability of the foam does not depend on individual factors in a linear manner. You can't just change one thing and get it right.— Jan Vermant, Professor of Soft Materials at ETH Zurich
The Hearth Conversation Another angle on the story
Why did it take seven years to understand something people have been drinking for centuries?
Because the foam itself is simple to observe but the physics underneath is genuinely complex. For decades, scientists thought they had it figured out—proteins around bubbles, done. But when they actually measured what was happening, they found different beers were doing completely different things.
So a Tripel and a lager are using different physics to stay foamy?
Entirely different. A lager relies on protein stiffness—more protein, stiffer bubble shell, longer foam. A Tripel barely uses that mechanism at all. Instead, it uses surface tension variations to create currents that hold the bubbles together. It's like comparing a rigid structure to a dynamic flow.
Can a brewer just add more protein to make better foam?
No, and that's the crucial insight. If you add more surfactants to increase viscosity, you might actually destroy the foam because you're interfering with the surface tension effects that were keeping it stable. You have to understand which mechanism your beer relies on, then work within that system.
Does this matter only for taste, or is there something else?
In Belgium, foam is part of the drinking experience—taste, texture, tradition. But it's cultural. In other places, foam barely matters. What's genuinely interesting is that this research is now being used to solve problems in electric vehicle lubricants and to develop better surfactants for industrial use.
So a Belgian brewer's casual comment about watching the foam led to applications in car engines?
Exactly. That's how science works sometimes. You start with a simple question, you follow it carefully for seven years, and suddenly you're helping solve problems in completely different industries.