There is something undeniably satisfying about a freshly poured beer. The golden liquid sparkles in the glass, tiny bubbles rise, and at the very top sits a crown of foam—light, creamy, and inviting. For beer lovers, that foamy head is more than decoration. It’s part of the ritual, a signal that the brew is alive, fresh, and full of character.
But anyone who drinks lager knows the disappointment: just moments after pouring, the head collapses, leaving a flat surface and a less appealing experience. Belgian beers, however, seem to break the rules. Their foam can last far longer—sometimes holding firm until the last sip. For years, brewers and scientists wondered why.
Now, thanks to researchers at ETH Zurich led by Professor Jan Vermant, we have an answer. And what they found goes beyond beer—it reveals fundamental principles of physics, chemistry, and even hints at future innovations in technology and the environment.
Foam as a Window Into Fermentation
The story began with a simple question Vermant asked a Belgian brewer: “How do you control fermentation?” The brewer’s reply was short and poetic—“By watching the foam.”
This wisdom sparked seven years of research. Foam, it turns out, is not just an aesthetic flourish but a complex, scientific phenomenon that reflects what’s happening inside the beer. The secret lies not only in bubbles but also in the proteins, chemical forces, and fermentation processes that shape them.
Why Some Beers Hold Foam Better
The ETH team discovered that foam stability differs dramatically depending on how the beer is fermented. Single-fermentation lagers produce the weakest and shortest-lived foam. Double-fermented beers hold up better. And triple-fermented Belgian beers—especially Trappist brews—create foam so resilient it seems almost magical.
At first, scientists assumed that foam stability was all about protein-rich films coating the bubbles. Proteins from barley malt were thought to influence how sticky or viscous the bubble surfaces became, which in turn helped the foam last longer. But Vermant’s team showed that the real story is more complex.
Surface Stress vs. Stickiness
For lager beers, the old theory holds true. Foam stability comes mostly from protein films that make bubble surfaces thicker and more resistant to collapse. But in Belgian Trappist-style beers, a different mechanism dominates.
Here, the foam is stabilized by Marangoni stresses—tiny currents that form when surface tension varies across a liquid’s surface. Imagine sprinkling crushed tea leaves on water, then adding a drop of soap. The sudden change in surface tension pulls the leaves outward, creating flows that keep the surface active. In Belgian beer, similar currents swirl around the bubbles, preventing them from popping too quickly.
This discovery revealed that Belgian beer foam doesn’t need heavy, sticky protein films. Instead, it thrives on the dynamic forces created during fermentation.
The Role of a Special Protein
At the heart of the process is a protein called Lipid Transfer Protein 1 (LTP1). It behaves differently depending on how many times the beer ferments:
- In lagers, LTP1 remains in its natural form, acting like tiny spheres that pack around the bubble surface. This forms a protective layer, but not a very strong one.
- In double-fermented beers, yeast activity alters the protein slightly, turning it into a flexible, net-like structure. This network makes bubbles harder to break.
- In triple-fermented beers, LTP1 proteins are transformed even further, breaking into fragments with one water-loving side and one water-repelling side. These fragments act like surfactants—the same kind of molecules used in soaps and detergents—to dramatically lower surface tension and maximize foam stability.
In short: the more a beer ferments, the more the proteins evolve, and the stronger and longer-lasting the foam becomes.
More Than Just Brewing
While this research may delight beer enthusiasts, its impact stretches far beyond the pub. Understanding foam stability has important implications for technology, manufacturing, and even sustainability.
In electric vehicles, for example, lubricants can sometimes foam, causing dangerous malfunctions. If scientists can learn how to destabilize foams as effectively as Belgian beer stabilizes them, these problems could be avoided.
The same principles apply to the development of eco-friendly surfactants—molecules that stabilize foams in products like detergents, shampoos, or even fire-fighting foams. By mimicking what happens naturally in beer, researchers may design new sustainable alternatives to fluorine- or silicon-based chemicals.
There are also promising applications in food science, where researchers are already studying milk foam in cappuccinos using lessons learned from beer. And in biotechnology, foams could be used to host bacterial systems for environmental or industrial purposes.
A Cultural Dimension of Foam
Of course, beer is not only about science—it’s also about culture. In Belgium, the foam is part of the drinking experience. A lasting head signals quality, enhances aroma, and adds texture to every sip. In other countries, however, foam is less celebrated. Some drinkers even see it as a nuisance.
This difference highlights how deeply food and drink are tied to tradition and perception. What one culture treasures as a sign of craftsmanship, another might ignore entirely. Yet, in both cases, the same science lies behind the bubbles.
The Beauty in the Bubbles
Foam may look simple, but it’s a delicate balance of forces, molecules, and physics. Behind every pint poured lies a dance of proteins and stresses, forming a fleeting yet beautiful structure that says much about both nature and human ingenuity.
For beer lovers, this means that next time you lift a glass of Belgian Trappist ale and admire its thick, creamy foam, you’re not just enjoying a drink—you’re witnessing the hidden work of proteins, yeast, and physical laws.
And for science, it means that even in something as everyday as beer, there are discoveries waiting that can reshape technology, protect the environment, and deepen our appreciation for the complexity of the world.
So the next time foam lingers at the top of your glass, let it remind you: science is everywhere, even in the simple pleasure of a summer beer.
More information: The Hidden Subtlety of Beer Foam Stability: A Blueprint for Advanced Foam Formulations, Physics of Fluids (2025). DOI: 10.1063/5.0274943
