How do you get a nice head of foam on a draft beer? – New Scientist

A properly poured beer has a nice head. But how do you ensure that if you don’t pour the beer into the glass from above, but from the bottom: bottom up?

‘Due to a head of foam, the refreshing, sparkling carbon dioxide and the taste evaporate less quickly from your beer. In addition, it is the very first sensory impression of the beer, even before consumption’, mails Wenjing Lyu, from the South Korean research institute LSTME Busan. So are foam collars big business.

The creation of the foam head is a complex process. That is why the German beer tap start-up Einstein 1 approached Lyu’s research group. Together they developed a model that predicts foam formation for their particular tapping method.

Bottom up

The startup is developing a tap system that fills a beer glass from the bottom. The idea arose during the Covid-19 pandemic when hygiene was suddenly in the spotlight. The bottom-up tap system works with a specially designed glass that you press onto the tap. The nozzle then pushes up a movable magnet on the bottom of the glass so that the beer can flow inside. When the glass is filled, the magnet drops back and your beer is ready to drink.

Anyone can tap beer during a festival or in their own kitchen. No one else needs to touch the glass. ‘In addition, the purpose of the tap is to be able to fill the glass as quickly as possible with a high reproducibility of the foam formation,’ says Lyu. This would also eliminate the need for skimming, for example, so that less beer is wasted.

The researchers conducted experiments with this tapping system to create a computer model that describes the foam formation and behavior, such as how firm it is and how quickly it disappears.

Foam collar

Beer foam is created by gas bubbles, mainly CO₂, which bubble up. These gas bubbles create a foam layer on the surface because they take along proteins, barley and hop residues along the way. The proteins in particular form a solid layer around the carbon dioxide bubbles. The precise ingredients of the beer determine how firm the head is.

With the tapping technique of Einstein 1, the experiments showed that the foam layer is formed in the first 1.5 to two seconds. After that, only liquid beer is added. This has to do with the fact that the beer can no longer splash freely against the glass, because there is already a layer of foam on it. This is comparable to when you pour beer into your glass at an angle. In addition, the beer initially also splashes around more, creating the foam.

How much foam is formed depends on the pressure and temperature. Higher pressures and temperatures result in more foam. With more pressure from the tap, the beer splashes around more, and at higher temperatures the carbon dioxide bubbles up faster.

Nozzle

With the tapping technique of Einstein 1, foam formation can therefore be controlled by adjusting the pressure. In addition, the researchers are now also looking at the shape of the nozzle. This determines whether the beer flows turbulently, or wildly swirling, into the glass, creating more foam, or whether the flow is more even, so that the beer foams less.

Lyu: ‘That means, for example, that you can also create sufficient foam with beer that contains little carbon dioxide, just by changing the shape of the mouthpiece.’ Exactly what shapes the mouthpiece should have for this is still being researched.