Summertime is beer time—even if the consumption of alcoholic beer is declining in Switzerland. And for beer lovers, there is nothing better than a head of foam topping the golden, sparkling barley juice. But with many beers, the dream is quickly shattered, and the foam collapses before you can take your first sip. There are also types of beer, however, where the head lasts a long time.
Summertime is beer time—even if the consumption of alcoholic beer is declining in Switzerland. And for beer lovers, there is nothing better than a head of foam topping the golden, sparkling barley juice. But with many beers, the dream is quickly shattered, and the foam collapses before you can take your first sip. There are also types of beer, however, where the head lasts a long time.
ETH researchers led by Jan Vermant, professor of soft materials, have now discovered just why this is the case. Their study has just been published in the journal Physics of Fluids. The Belgian researcher and his team put seven years of work into these issues. It all started out with a simple question put to a Belgian brewer: « How do you control fermentation?—By watching the foam », was the succinct reply.
Today, ETH scientists understand the mechanisms at work behind perfect beer foam. And perhaps future beer drinkers will be able to admire the head of foam in their glasses a little longer before quenching their thirst.
In this study, the materials scientists showed that Belgian beers that have been triple fermented have the most stable foam, followed by double fermented beers. The head is least stable in single fermented lager beers.
Triple-fermented beers include Trappist beers, a specialty of the eponymous monastic order. A beer from a large Swiss brewery was also among the lager beers the ETH researchers examined. « There is still room for improvement—we are happy to help », says Vermant.
To date, researchers assumed that the stability of beer foam depended primarily on protein-rich layers on the surface of the bubbles (see ETH News): proteins come from barley malt and influence surface viscosity, i.
