Beer head

Beer head (also head or collar)[1] is the frothy foam on top of beer and carbonated beverages which is produced by bubbles of gas, predominantly carbon dioxide, rising to the surface.

The elements that produce the head are wort protein, yeast and hop residue.

The density and longevity of the head will be determined by the type of malt and adjunct from which the beer was fermented.

In general, wheat tends to produce larger and longer-lasting heads than barley.

The beer head is created by the carbon dioxide produced as a byproduct of the metabolism of brewer's yeast acting upon starches and sugars found in the wort.

Beer foam consists of polypeptides of five different classifications, divided by their relative hydrophobicity.

Many other properties of the glass can also influence a beer head,[6] such as a roughened surface at the base of glass known as a widget, providing for nucleation of carbon dioxide deep in the beverage rather than at the surface, resulting in a slower release of gas to the atmosphere.

Conversely, some styles such as Belgian witbier benefit from being poured into a wet glass to control the often abundant head.

The use of nitrogen, which was pioneered by Guinness, creates a firm head with small bubbles while reducing the excessively acidic taste often produced by using carbon dioxide alone.