Scientists at ETH Zurich have identified the physical mechanisms that determine beer foam stability after a seven-year study. Their research explains variations across beer styles, from Belgian ales to Swiss lagers. The findings, published in Physics of Fluids, offer insights for brewers and broader applications.
The quest to understand beer foam began with a simple exchange between ETH Zurich researchers and a Belgian brewer. When asked how brewing is controlled, the brewer replied, "By watching the foam." This prompted a seven-year investigation led by Jan Vermant, Professor of Soft Materials, into the forces sustaining a beer's head.
Published in the journal Physics of Fluids, the study analyzed Belgian ales and Swiss lagers. Among Belgian styles, Tripel beers exhibited the most stable foam, followed by Dubbel, with Singel showing the least durability due to milder fermentation and lower alcohol content. The researchers tested two lagers from major Swiss breweries, finding one underperformed. Vermant noted, "There is still room for improvement -- we are happy to help."
Traditional views held that foam stability stemmed from protein-rich layers from barley malt affecting surface viscosity and tension. However, the experiments revealed greater complexity tied to beer type. In lagers, surface viscoelasticity governs stability, influenced by protein quantity and denaturation, creating stiffer bubble films. Tripel beers, conversely, depend on Marangoni stresses, where surface tension variations induce stabilizing currents, akin to soap disrupting tea leaves on water.
The protein LTP1 emerged as key, varying in structure and concentration across samples. Bubble shells in Singel beers mimic packed particles, Dubbel forms mesh-like membranes, and Tripel behaves like simple surfactants.
Foam stability proves nonlinear, as Vermant explained: "The stability of the foam does not depend on individual factors in a linear manner. You can't just change one thing and get it right." The team collaborated with a major global brewery to refine foam quality, emphasizing cultural importance in places like Belgium.
Beyond brewing, the research aids in managing lubricant foams in electric vehicles, developing eco-friendly surfactants without fluorine or silicon, and stabilizing milk foam. Vermant highlighted, "Beer obviously does this well by nature!"