For many beer drinkers the ‘head’ on a glass of beer is critical. Too foamy or no foam at all can make the beer drinker unhappy, and along with the smell and the appearance, the foam at the top is an important part of the beer drinking experience.
According to the research brief
, it is the proteins from the barley and yeast (Saccharomyces pastorianus
) used to make beer that contribute to the quality of the foam. The foamy head on a glass of beer consists of small bubbles containing carbon dioxide gas. The gas is produced by yeast during fermentation. Proteins gather around the gas, forming the bubbles in the foam.
Foam also relates to the level of alcohol. Foam will not last if the alcohol level is too high (such as Belgian beer in the 9-12 percent alcohol range) or too low (like a Bud Light at 3.2 percent). The optimal level for alcohol is around 5 percent, according to researcher Katharine Gammon
The beer yeast, Saccharomyces pastorianus
is a synonym of the yeast species Saccharomyces carlsbergensis
, which was originally described
in 1883 by Emil Christian Hansen, who was working for the Danish brewery Carlsberg. Sometimes other yeasts are used to make beer (the Digital Journal
noted recently that a man used a yeast found in his own beard to brew up a golden ale).
Whilst scientists have known for some years that proteins from the yeast help to stabilize the foam, preventing the head from disappearing too soon, it was not known, until recently, which yeast gene was responsible for making the foam-stabilizing protein.
The researchers identified the gene, (called CFG1). The gene is similar to those already identified in wine and sake yeasts that also are involved in foaming. The research was led by Tomás G. Villa. The findings have been published
in the ACS Journal of Agricultural and Food Chemistry.