Bitter compounds found in hops, like iso-alpha acids, are important to brewers, said Karl J Siebert, principal investigator from the Cornell University.
"Dissolved gases in the beer - carbon dioxide and, in some instances, nitrogen - play a role. So do acidity, some ions, ethanol levels, viscosity and numerous other factors that have been tried by brewers and scientifically tested," said Siebert, professor of food science and technology at the New York State Agricultural Experiment Station in New York.
"But LTP1 (barley lipid transfer protein No 1) is the key to perfect beer foam," said Siebert.
Fascinating as foam is to chemists, LTP1 is of vital importance for the sensory experience of beer appreciation, said Siebert, formerly a longtime research chemist in the industry.
"To some beer aficionados, the sign of a good head - the proper consistency, colour, height, duration - is to draw a face with your finger in the foam, before taking the first sip," the food scientist noted.
"If the face is still there, when the glass is drained and the liquid is gone - that's seriously good foam," said Siebert.
The study was published in the Journal of the American Society of Brewing Chemists.