What Is Beer Foam?February 2, 2012 # 4:00 AM # Brewing Analyses # One Comment
Beer foam is a major characteristic of beer, which is a sudden decrease of pressure, whether it’s in a bottle, can or keg. The carbon dioxide dissolved in the beer turns to gas and forms bubbles that rise to the surface.
Other substances in the beer such as small protein and some polyphenol can form an elastic skin around the bubbles as they rise so that the bubbles pile up at the top of the beer and create foam.
The characteristics of foam experienced by the consumer are:
1. Amount of foam head formed – (volume)
2. Stability or collapse time (head retention)
3. Texture – is it rich creamy foam or a coarse one?
4. Cling – the adherence to the glass surface.
Formation of beer foam depends on the volume of CO2-gas liberated at the moment of pouring.
The volume of CO2 bubbles depends on the content of CO2 dissolved in the beer and the temperature of the beer. Furthermore, it depends on how the beer is poured into the glass.
If the beer is poured gently without liberating any CO2, no foam is developed. When beer is allowed to fall freely into a glass, a large amount of foam is developed.
After pouring and formation of beer foam the foam is allowed to collapse over a period of time. The time it takes to reduce the amount of foam to the half is called the half-time or head retention.
Consumers tend to place a lot of importance on beer foam: too much of foam is undesirable because it detracts from the mass of the drink, but on the other hand, a beer drink is viewed as incomplete unless it has foam, and the specific form of head expected for the type of beer. So what does the head on a glass of beer do? Is it, as many people feel, a barrier to the beer, at best a moustache decorator? Is it just for looks, or is there a deeper reason? Not everyone demands a good foamy glass, and there are local variations. Some view beer heads as important because they give off the aroma of the beer. Another opinion is that it is important for the aesthetic look of the beer.