Researchers Unveil Science Behind Long-Lasting Beer Foam

Scientists at ETH Zurich have made significant strides in understanding the science behind beer foam. Their research delves into the mechanisms that determine why some beers maintain a thick, stable layer of foam while others do not. This discovery is particularly important for both brewers and beer enthusiasts, as it enhances the overall drinking experience.

For many beer drinkers, a glass feels incomplete without a rich layer of foam. However, this foam often dissipates quickly, leaving drinkers disappointed. The team spent seven years conducting detailed investigations to uncover the factors that contribute to the longevity of beer foam.

The inquiry began with a simple question posed to a Belgian brewer: “How do you control brewing?” The response was enlightening—”By watching the foam.” This sparked a comprehensive study into the physical principles that govern foam stability in various beer styles.

Understanding Foam Stability

The researchers focused on Belgian ales, categorizing them into three types: Tripel, Dubbel, and Singel. Their findings revealed a clear hierarchy in foam stability. Tripel beers produced the most enduring foam, followed closely by Dubbel beers, while Singel beers demonstrated the least stability due to lower fermentation levels and alcohol content.

In addition to Belgian ales, the study also evaluated two lagers from prominent Swiss breweries. While these lagers achieved comparable foam stability to the Belgian styles, the underlying physical principles were distinctly different, with one lager performing noticeably worse.

For years, the prevailing belief was that beer foam stability largely depended on protein-rich layers surrounding each bubble. These proteins, derived from barley malt, influence surface viscosity and surface tension. However, the new experiments indicate that foam stability is influenced by a variety of complex factors, particularly the beer style itself.

The Role of Proteins and Surface Forces

In lager beers, the property of surface viscoelasticity plays a critical role in maintaining foam stability. This characteristic relies on the protein content and how these proteins behave when denatured. Higher levels of protein create a stiffer film around the bubbles, enhancing foam durability.

Conversely, Tripel beers depend less on surface viscoelasticity. Instead, they maintain their foam primarily through Marangoni stresses, which arise from variations in surface tension across the liquid’s surface. This phenomenon, known as the Gibbs–Marangoni effect, facilitates the movement of liquid along interfaces, significantly contributing to foam longevity.

The researchers discovered that foam stability is closely linked to the structure and behavior of the protein-rich shells around each bubble. In Singel beers, these shells function similarly to tightly packed spherical particles, helping to maintain foam. Dubbel beers demonstrate a different pattern, where the proteins form a mesh-like structure that further reinforces the bubbles. In contrast, the dynamics of Tripel beers resemble those of common surfactants used in everyday foam stabilization products.

While the precise reasons behind these differences continue to be explored, one protein, LTP1 (lipid transfer protein 1), appears to play a significant role in foam stability. The research indicates that increasing the amount of surfactants in beer to enhance viscosity may paradoxically destabilize the foam by interfering with Marangoni effects.

The findings of this extensive study are published in the journal Physics of Fluids under the title “The hidden subtlety of beer foam stability: A blueprint for advanced foam formulations.” This research not only sheds light on the intricacies of beer foam but also holds potential implications for the brewing industry, paving the way for advanced formulations that enhance the beer-drinking experience.