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After an extensive seven-year investigation, scientists at ETH Zurich have discovered the long-sought formula for stable beer foam, often referred to as the "holy grail" of brewing. This research provides insights into the different physical mechanisms that contribute to the durability of foam across various beer types.

The project, led by Professor Jan Vermant, was inspired by a fundamental question posed to a Belgian brewer: "How do you control brewing?" The response was telling—"By watching the foam." This interaction led the researchers to explore the forces and structures behind the foam stability that keeps beer enjoyable from the first sip to the last.

Their findings, published in Physics of Fluids, reveal a clear hierarchy in foam stability among different Belgian ales. The "Tripel" style produced the most stable foam, followed by "Dubbel," with "Singel" beers exhibiting significantly less durability owing to milder fermentation processes and lower alcohol levels.

In examining two lagers from large Swiss breweries, the team noted that while these lagers can achieve stable foam akin to Belgian ales, the underlying physical principles differ. One lager’s performance was less impressive than anticipated, highlighting potential for further improvement.

Traditionally, foam stability was largely attributed to protein-rich layers forming around bubbles, derived from barley malt. However, this study uncovers a complex interplay of factors influencing foam longevity, especially depending on the type of beer.

In lagers, foam stability is determined by surface viscoelasticity, significantly influenced by protein amounts and their behavior. In "Tripel" beers, stability is maintained through Marangoni stresses—movement caused by surface tension variations. This can be illustrated with a simple analogy: when soap is added to a surface of crushed tea leaves on water, the leaves are drawn outward by swirling currents, which can help stabilize foam similarly to "Tripel" beers.

Researchers discovered that the structural behavior of proteins surrounding the bubbles differs for each beer type. In "Singel" beers, these proteins create a densely packed formation, while "Dubbel" beers develop a mesh-like structure that enhances stability. In contrast, "Tripel" beers mimic properties of surfactants used in various products.

The ETH team has partnered with a leading brewery to delve deeper into the foam stability issue and ascertain the factors that keep beer foam from collapsing. Vermant asserts that enhancing foam quality requires a careful, structured approach rather than a one-size-fits-all method.

Beyond brewing, the research has wider implications. For instance, in electric vehicles, foams in lubricants can pose risks, and the team has begun collaborating with Shell to explore solutions for foam management. Additionally, they are studying the use of environmentally friendly surfactants and investigating the stabilization properties of foams in various contexts, emphasizing the valuable insights gained from their beer research.

In summary, this comprehensive study enriches our understanding of beer foam stability and paves the way for advancements not just in brewing but across various industries.