Scientists have uncovered the secret to the persistent foam in Belgian beer

Researchers at the Swiss ETH Zurich, led by Professor Jan Wehrmann, have conducted a seven-year study to provide a scientifically sound answer to this question. The results are published in the journal Physics of Fluids.

It all started with a simple question to a brewer in Belgium: "How do you control the fermentation process?" - "By the foam," he replied. It turned out that the stability of the foam hides complex physical and chemical processes that depend on the number of fermentation stages and the proteins present in the beer.

Belgian beers with triple fermentation (e.g. Trappist beers) have the most stable foam, followed by those with double fermentation. Single fermentation lagers are the least foamy. Researchers also studied the products of a major Swiss brewery, noting that their foam is still far from ideal.

It was previously thought that the persistence of foam depends on the viscosity of the film on the bubbles - proteins in the malt thicken the shell and hold the foam together. However, scientists have discovered that this is not the case with triple fermentation beers. Here, the so-called Marangoni effects - surface currents arising from differences in surface tension - play a major role. These currents stabilise the bubbles and prevent the foam from collapsing.

The scientists paid special attention to the LTP1 (lipid-transport protein 1) protein. In lagers, it retains its original structure and behaves as microscopic spheres forming a dense protective layer on the surface of the bubbles. During double fermentation, the proteins are slightly modified to form a reticulated structure that enhances the protection. After the third fermentation, LTP1 breaks down into fragments, one end of which attracts water and the other end repels it. This makes the foam as stable as possible - similar to the action of surfactants in household detergents.

Scientists note that beer foam is not just about aesthetics. The same mechanisms are important in mechanical engineering, ecology and the food industry. For example, in electric cars, excessive foam in lubricants can be dangerous. The ETH Zurich team is collaborating with Shell and other companies to use the knowledge gained to manage foaming. Protein-based biofoams for the dairy industry and sustainable surfactants without fluorine and silicone are also being investigated.

As Professor Wehrmann concludes, "beer itself has found an effective way to manage complex mechanisms - we just have to learn from it."