Researchers Unveil Science Behind Beer Foam Stability

An extensive seven-year study by researchers at ETH Zurich has revealed the scientific principles behind the stability of beer foam, a key aspect of the brewing process. This research identifies the various physical mechanisms that contribute to the longevity of foam in different beer styles, shedding light on why some beers maintain their frothy heads longer than others.

For many beer enthusiasts, a glass of beer is incomplete without a thick, creamy foam topping. Yet, this desirable foam often dissipates rapidly, leaving drinkers disappointed. The new findings provide clarity on the factors influencing foam stability, an area that had puzzled experts for years.

Understanding Beer Foam Dynamics

The journey towards this discovery began with a simple inquiry posed to a Belgian brewer: “How do you control brewing?” The brewer’s succinct response, “By watching the foam,” laid the groundwork for a comprehensive exploration into the science of beer. This research focused particularly on Belgian ale varieties, revealing a clear hierarchy in foam stability among them.

The study found that Tripel beers exhibit the most stable foam, followed by Dubbel beers, while Singel beers show the least durability due to milder fermentation processes and lower alcohol content. The researchers also tested two lagers from major Swiss breweries, noting that while these lagers can achieve foam stability comparable to Belgian ales, the underlying physics differ significantly, with one lager performing notably worse.

Complexities of Foam Stability

Traditionally, scientists attributed foam stability to protein layers that encircle each bubble, derived from barley malt. These proteins were thought to affect surface viscosity and tension, crucial factors for foam retention. However, the latest experiments indicate a more intricate relationship between foam stability and beer style.

In lagers, for instance, foam stability hinges on surface viscoelasticity, which is influenced by both the quantity of protein and the manner in which these proteins denature. Higher protein concentrations yield a stiffer film around bubbles, enhancing foam retention.

Conversely, Tripel beers do not rely heavily on this viscoelasticity. Instead, they maintain foam through Marangoni stresses, which occur when differences in surface tension cause movement across the liquid surface. This effect was first noted in the context of the “tears of wine” phenomenon.

The research highlights that the behavior of protein-rich shells surrounding bubbles is critical to foam stability. In Belgian Singel beers, these shells behave like tightly packed spherical particles, resembling a two-dimensional suspension, which supports foam longevity. Dubbel beers, on the other hand, exhibit a mesh-like membrane that further reinforces bubble stability.

The precise mechanisms behind these differences are still being explored. Initial findings suggest that a specific protein, LTP1 (lipid transfer protein 1), plays a significant role. The study also notes that increasing viscosity by adding more surfactants may destabilize foam, as this can interfere with Marangoni effects.

The results of this research, published in the journal Physics of Fluids under the title “The hidden subtlety of beer foam stability: A blueprint for advanced foam formulations,” offer valuable insights for brewers seeking to enhance the quality of their products.

As beer drinkers continue to seek out the perfect pour, the findings from ETH Zurich provide a scientific foundation that could improve the brewing process and the overall drinking experience.