Unveiling the Secrets of Beer Foam: A 7-Year Study
Many beer enthusiasts know the frustration of a glass that feels empty without a thick, creamy foam on top. Yet, this foam often vanishes quickly, leaving you with a bitter taste of disappointment. But what if there was a way to keep that frothy head around for longer? A groundbreaking 7-year study by researchers at ETH Zurich, led by Professor Jan Vermant, has uncovered the science behind the varying foam stability in different beer styles.
The study began with a simple question to a Belgian brewer: How do you control brewing? The brewer’s response was enlightening: ‘By watching the foam.’ This led the researchers to delve into the fascinating world of beer foam, discovering that its stability is far from simple.
The Foam Hierarchy: Tripel, Dubbel, and Singel
In their analysis of Belgian ales, the scientists identified a clear hierarchy of foam stability. ‘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. This finding highlights the intricate relationship between beer style and foam retention.
The study also evaluated two lagers from large Swiss breweries, revealing that while these lagers can achieve foam stability similar to Belgian ales, the underlying physics differ significantly. One lager performed noticeably worse than expected, leaving room for improvement.
The Role of Proteins and Surface Forces
For years, scientists believed that beer foam’s stability was primarily due to protein-rich layers surrounding each bubble. These proteins, derived from barley malt, influence the bubble surface’s flow and surface tension. However, the new experiments show that foam stability is more complex and highly dependent on beer style.
In lager beers, foam stability is controlled by surface viscoelasticity, which depends on protein content and denaturation. Higher protein levels result in a stiffer film around bubbles, enhancing foam longevity. In contrast, ‘Tripel’ beers rely less on surface viscoelasticity, maintaining foam through Marangoni stresses, forces generated by surface tension variations.
A simple demonstration of Marangoni stresses involves placing crushed tea leaves on water. When a drop of soap is added, the leaves are pulled outward, creating swirling currents that help steady the bubbles, similar to ‘Tripel’ foam.
The Inner Bubble Shells: Unraveling Beer Behavior
The researchers discovered that foam stability depends on the structure and behavior of protein-rich shells surrounding each bubble. In ‘Singel’ beers, these shells behave like a two-dimensional suspension, tightly packing spherical particles across the bubble surface, which aids in foam retention.
‘Dubbel’ beers exhibit a different pattern, with proteins forming a mesh-like membrane that further strengthens the bubbles. ‘Tripel’ beers stand out, with bubble dynamics resembling those of simple surfactants, commonly used to stabilize foams in everyday products.
The precise reasons for these differences remain under investigation, but one protein, LTP1 (lipid transfer protein 1), appears to play a significant role. The ETH researchers confirmed this by examining the structure and concentration of LTP1 in Belgian samples.
Collaborating for Better Foam: A Brewery Partnership
Professor Vermant emphasizes that foam stability is not influenced linearly by individual factors. He advises against making multiple changes simultaneously, as it may lead to instability. For instance, adding more surfactants to increase viscosity might destabilize the foam by interfering with Marangoni effects.
To address this, the ETH team partnered with a major brewery to understand foam stability and identify the key factors keeping beer foam from collapsing. By uncovering the precise physical mechanism, they can now help the brewery improve foam quality.
In Belgium, foam is valued for both taste and the overall drinking experience, but its importance varies across cultures. Beyond brewing, the research has practical applications, such as understanding and mitigating foaming in electric vehicles and developing environmentally friendly surfactants.
Beyond Brewing: Foam Science in Industry and Environment
The study’s implications extend beyond the brewing industry. Vermant’s group is collaborating with Shell and other partners to break down foams efficiently in electric vehicles, where lubricants can pose risks. They are also developing environmentally friendly surfactants, free from fluorine and silicon.
Additionally, the team is investigating foams as carriers for bacterial systems in an EU project, collaborating with food researcher Peter Fischer from ETH Zurich. They are studying how proteins can stabilize milk foam, showcasing the versatility of foam science.
In conclusion, the 7-year study has unlocked the secrets of beer foam stability, offering insights that go beyond brewing. The knowledge gained from this research has the potential to revolutionize various industries, from automotive to food, and even environmental science.