Scientists uncover the mechanics behind the perfect beer foam

Brewers have long considered beer foam as a quick readout of a fermentation that’s gone right, yet the physics and chemistry that keep those bubbles from collapsing have remained oddly elusive.

Now, a seven-year investigation led by ETH Zurich, with collaborators at Eindhoven University of Technology and several European observatories of beer variety, has pinned down why some foams vanish in a blink while others linger.

The answer blends cutting-edge microscopy with old-world brewing styles – and it has implications far beyond the tap.

How beer foam resists collapse

Foam is a jam-packed city of air bubbles, each one walled off from its neighbors by nanometer-thin liquid films. Those films must resist rupture; if they thin too fast or lose strength, the foam drains and collapses.

In the journal Physics of Fluids, the team reported how they used high-resolution imaging and rheometry to watch, in real time, what happens where it matters most: the narrow “neck” where two neighboring bubbles press together.

“We can directly visualize what’s happening when two bubbles come into close proximity,” said ETH researcher Emmanouil Chatzigiannakis. “We can directly see the bubble’s protein aggregates, their interface, and their structure.”

Beer, it turned out, was the perfect model foam: endlessly reproducible, richly variable across styles, and naturally loaded with the proteins and surface-active molecules that tune thin-film behavior.

Beer foam stability depends on style

The group put a spectrum of beers under the microscope, from single-fermented lagers to double- and triple-fermented Belgian ales. That stylistic ladder became a physics ladder.

In single-fermentation lagers, foam stability depended chiefly on surface viscosity – the “stickiness” at the bubble interface imparted by malt-derived proteins. The more robust that interfacial viscosity, the longer the walls resisted thinning and popping.

Double-fermented ales, by contrast, told a different story. Here, proteins at the interface didn’t just thicken the surface; they knit together into two-dimensional, net-like structures – elastic skins that endowed the film with tensile strength. Elasticity worked like a trampoline, holding films together against gravity’s pull and drainage.

Triple-fermented Trappist-style beers went a step further. In these, the team found that surface viscosity was minimal. The foam’s staying power came from Marangoni stresses.

When surface tension varies, fluid flows and circulating currents replenish thinning spots. Sprinkle tea leaves on water and add soap – the fragments rush outward as invisible surface currents form. In these richly fermented ales, persistent Marangoni flows stabilized the bubble walls for the long haul.

One protein, three roles

Threading through all three regimes was a single malt protein with many aliases in the literature – LTP1 (lipid transfer protein 1). Its state of “denaturation,” or unfolding, shifted with each fermentation step and rewrote its interfacial job description.

In single-fermented lagers, LTP1 largely retains its native, compact shape. At the bubble surface, these near-spherical particles pack into a dense, two-dimensional suspension, boosting surface viscosity and slowing film drainage.

A second fermentation nudges LTP1 out of that tidy conformation. Yeast activity and the evolving beer chemistry partially denature the protein so it links into mesh-like networks – true interfacial membranes that lend elasticity to the film, the key to the double-fermented foam’s resilience.

A third fermentation pushes the transformation further. LTP1 fragments now present both water-loving and water-repelling ends, behaving like bona fide surfactants. These pieces actively lower interfacial and surface tensions, seeding the gradients that drive Marangoni flows.

“These protein fragments function like surfactants, which stabilize foams in many everyday applications, such as detergents,” noted ETH professor of soft materials Jan Vermant, who led the study.

The net result tracks what beer lovers observe in the glass: triple-fermented Belgian ales show the most persistent heads, followed by double-fermented styles. Single-fermented lagers, including a major Swiss brand the team examined, tend to lose their foam fastest.

Viscosity, elasticity, and flows

If you’re tempted to “just add more surfactant” or “just crank up viscosity,” the data examined suggests not to do so. Foam stability doesn’t respond linearly to single tweaks, and the mechanisms can work at cross-purposes.

In lagers, for instance, boosting viscosity can help, but doing so in a system that relies on Marangoni flows may backfire by damping the very surface currents that keep the film alive.

“The key is to work on one mechanism at a time – and not on several at once. Beer obviously does this well by nature,” Vermant said.

That mechanistic clarity emerged only because the team could watch films evolve in situ. By pairing optical and interfacial measurements, they identified when viscosity dominated.

The researchers saw when flows driven by elasticity and surface-tension ruled. They also confirmed LTP1’s starring role by analyzing protein content and state across styles.

From the brewhouse to broader tech

The work began, fittingly, with a brewer’s rule of thumb. Asked how he controlled fermentation, a Belgian brewer said: ‘By watching the foam.”

The scientists’ answer, years later, explains why that intuition works and how to engineer it. ETH’s group has already partnered with one of the world’s largest breweries to translate the physics into process tweaks that enhance head retention without compromising flavor or stability.

But foam is a universal material, not just a beverage flourish. The lessons from beer apply to firefighting foams, oil–water separations, and even medical sclerosing agents used to treat varicose veins.

In electric vehicles, for example, gearbox lubricants can entrain bubbles and foam – an efficiency and durability risk.

Vermant’s team is working with industry partners, including Shell, to learn how to suppress unwanted foams by selectively targeting viscosity, elasticity, or Marangoni flows.

The researchers are also pursuing sustainable, fluorine- and silicon-free surfactants inspired by LTP1 fragments, and adapting protein-based strategies to stabilize other food foams such as milk. In an EU project, they’re exploring foam scaffolds as carriers for bacterial systems.

The recipe for lasting foam

For brewers, the take-home is both empowering and nuanced. Foam longevity comes from different routes in different styles: a viscous interface in lagers, an elastic protein membrane in double-fermented ales, and self-renewing surface flows in triple-fermented Trappist beers.

You don’t need to – and shouldn’t – force all three at once. Tune the route that fits your beer and your brand.

For drinkers, the science adds appreciation to the spectacle. That persistent cap on a golden pour isn’t just pretty; it’s a living laboratory of thin films, proteins, and surface physics.

Thanks to advanced imaging and monastic brewing traditions, we now know why some heads last while others fade. This knowledge could soon make perfect pours more common.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–