Seven-year study uncovers the holy grail of beer brewing

Researchers at ETH Zurich, led by Jan Vermant, Professor of Soft Materials, have uncovered the scientific explanation for these differences. Their work, published in the journal Physics of Fluids, is the result of seven years of detailed investigation. The idea for the study began with a straightforward question posed to a Belgian brewer: "How do you control brewing?" The brewer's answer was brief but revealing: "By watching the foam."

The research team now has a solid grasp of the forces and structures responsible for long-lasting beer foam, offering new insight into what keeps a beer's head intact.

Tripel, Dubbel, and Singel: Which Foams Hold Up Best

In their analysis of Belgian ales, the scientists found a clear hierarchy. "Tripel" beers produced the most stable foam, followed by "Dubbel" beers, while "Singel" beers had the least durable head due to milder fermentation and lower alcohol content.

The team also evaluated two lagers from large Swiss breweries. Although these lagers can achieve foam stability similar to Belgian ales, the physics behind them vary significantly. One lager performed noticeably worse than expected. As Vermant notes, "There is still room for improvement -- we are happy to help."

For many years, scientists believed that beer foam mainly stayed intact because of protein-rich layers that formed around each bubble. These proteins, which come from barley malt, can influence how easily the bubble surface flows (its surface viscosity) and its surface tension.

However, the new experiments show that foam stability is more complex than previously thought, and highly dependent on beer style.

How Proteins and Surface Forces Shape Foam Stability

In lager beers, foam stability is controlled by surface viscoelasticity. This property depends heavily on both the amount of protein in the beer and how these proteins denature. Higher protein levels result in a stiffer film surrounding the bubbles, which helps the foam last longer.

"Tripel" beers, by contrast, rely very little on surface viscoelasticity. Instead, they maintain foam through Marangoni stresses -- forces created when variations in surface tension generate movement across a liquid's surface.

A simple demonstration of this effect involves placing crushed tea leaves on water. At first, the pieces float evenly. When a drop of soap lands on the surface, the leaves are suddenly pulled outward, and swirling currents begin. When these currents persist, they help steady the bubbles, similar to what happens in "Tripel" foam.

Inside the Bubble Shells: Why Different Beers Behave Differently

The researchers found that foam stability depends on the structure and behavior of the protein-rich shells that surround each bubble. In Belgian "Singel" beers, these shells behave as though many small, spherical particles are tightly packed across the bubble surface. This resembles a two-dimensional suspension (a mixture of a liquid and very fine solids), which helps maintain foam.

"Dubbel" beers show a different pattern. Their proteins create a mesh-like membrane that strengthens the bubbles even more. "Tripel" beers again stand apart, with bubble dynamics resembling those of simple surfactants, the molecules commonly used to stabilize foams in everyday products.

The precise reasons for these differences have not been fully determined. Still, one protein, LTP1 (lipid transfer protein 1), appears to play a major role. The ETH researchers confirmed this by examining both the structure and concentration of LTP1 in the Belgian samples.

Partnering With a Major Brewery to Improve Foam Quality

Vermant emphasizes that foam stability is not influenced in a straightforward or linear way. "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." As an example, adding more surfactants to increase viscosity may actually destabilize the foam because it interferes with Marangoni effects. "The key is to work on one mechanism at a time -- and not on several at once. Beer obviously does this well by nature!" he explains.

The ETH team partnered with one of the largest breweries in the world to better understand foam stability and identify what actually keeps beer foam from collapsing. "We now know the precise physical mechanism and are able to help the brewery improve the foam on their beers," says Vermant.

He notes that, in Belgium, foam is valued for both taste and the overall drinking experience. "But foam isn't always important wherever beer is served -- it's a cultural thing."

Beyond Brewing: Foam Science in Industry and the Environment

The research has practical implications far beyond the brewing world. In electric vehicles, lubricants can begin to foam, which poses serious risks. Vermant's group is now working with Shell and other partners to understand how to break down these foams efficiently.

Another key objective is the development of environmentally friendly surfactants that do not rely on fluorine or silicon. "Our study is an important step in this direction," Vermant says.

The team is also investigating foams as carriers for bacterial systems as part of an ongoing EU project. In collaboration with food researcher Peter Fischer from ETH Zurich, they are studying how proteins can help stabilize milk foam. As Vermant concludes, "So there are many areas where the knowledge we have gained from beer is proving useful."