Credit: Personal Creations (CC BY 2.0)
The frothy layer of foam which sits at the top of a freshly poured glass of beer, known as the ‘head’, can reveal a lot about the beverage. Some beer enthusiasts prefer their heads larger and longer lasting, while others would rather forego the foam in favour of liquid.
New research examined several types of beer at different stages of the fermentation process to figure out the physics behind why some beer foams are so large and stable.
“The first thing that comes to mind when thinking of bubbles and foams is beer,” says study author Emmanouil Chatzigiannakis, an assistant professor at Eindhoven University of Technology in the Netherlands.
Foams consist of many small bubbles of gas separated by thin films of liquid. When these films become unstable, the bubbles pop and the foam collapses.
“The idea was to directly study what happens in the thin film that separates 2 neighbouring bubbles,” says Chatzigiannakis.
“We can directly visualise what’s happening when 2 bubbles come into close proximity. We can directly see the bubble’s protein aggregates, their interface, and their structure.”
Wave interference (interferometry) images of beer bubbles, superimposed onto a glass of foamy beer. Credit: AIP/Chatzigiannakis et al.
They found that the foams of single fermentation beers are held together mostly by the surface viscosity of the liquid. In contrast, the proteins in double-fermented beer come together to form 2-dimensional structures. This gives its thin films an elasticity that keeps them intact for longer.
“This is an inspiration for other types of materials design, where we can start thinking about the most material-efficient ways [of creating stable foams],” says co-author and chemical engineer Jan Vermant, a professor at ETH Zurich in Switzerland.
The formation and stability of foam is important to many industrial processes – including the production of certain plastics, cement, food, insulation and firefighting chemicals.
“If we can’t use classical surfactants, can we mimic the 2D networks that double-fermented beers have?”
The research has been published in the journal Physics of Fluids.