Beer head (also known as the
head) is produced by bubbles of
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
rising to the surface.
The density and longevity of the head will be determined by the type of malt and adjunct from which the beer was
fermentedFermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. A more restricted definition of fermentation is the chemical conversion of sugars into ethanol...
. Different mash schedules and cereal sources influence head retention.
In general, wheat tends to produce larger and longer lasting heads than barley.
The carbon dioxide may be produced naturally through the activity of brewers yeast, or artificially by
dissolvingSolvation, also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute...
carbon dioxide under pressure into the liquid.
Beer head (also known as the
head) is produced by bubbles of
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
rising to the surface.
The density and longevity of the head will be determined by the type of malt and adjunct from which the beer was
fermentedFermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. A more restricted definition of fermentation is the chemical conversion of sugars into ethanol...
. Different mash schedules and cereal sources influence head retention.
In general, wheat tends to produce larger and longer lasting heads than barley.
Formation through carbon dioxide
The carbon dioxide may be produced naturally through the activity of brewers yeast, or artificially by
dissolvingSolvation, also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute...
carbon dioxide under pressure into the liquid. The beer head is created by the
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
produced as a byproduct of the metabolism of brewer's yeast acting upon starches and sugars found in the
wortWort may refer to:* Wort, the liquid created by the mashing of malted barley to use in brewing beer* Wort plants, plants containing the middle English word wort in their names* WORT, a listener-sponsored community radio station in Madison, Wisconsin...
.
Chemical composition
While the actual foam activity of beer depends on the presence of carbon dioxide, it is the surface-active materials like amphipathic polypeptides from malt that determine size, shape and length of the foam.
Beer foam consists of polypeptides of five different classifications, divided by their relative hydrophobicity. As the hydrophobicity of the polypeptide groups increases, so does the stability of the foam.
Carbonation occurs when carbon dioxide is dissolved in water or an aqueous solution. This process is generally represented by the following reaction, where water and gaseous carbon dioxide react to form a dilute solution of carbonic acid.
Importance of the glass
Properties of the glass can also influence a beer head, with a roughened surface at the base of glass known as a
widgetA widget is a device placed in a container of beer to manage the characteristics of the beer's head. The original widget was patented in Ireland by Guinness. The "floating widget" is found in cans of beer as a hollow sphere, 3 cm in diameter .-Background:Draught Guinness, as it is known today, was...
, providing for
nucleationNucleation is the extremely localized budding of a distinct thermodynamic phase. Some examples of phases that may form via nucleation in liquids are gaseous bubbles, crystals, or glassy regions. Creation of liquid droplets in saturated vapor is also characterized by nucleation...
of carbon dioxide deep in the beverage rather than at the surface, resulting in a slower release of gas to the atmosphere.
While glass is completely nonporous, its surface can retain oil from the skin, aerosolized oil from nearby cooking, and traces of fat from food. When these oils come in contact with beer there is a significant reduction in the amount of head (foam) that is found on the beer, and the bubbles will tend to stick to the side of the glass rather than rising to the surface as normal.
For proper foam formation, it is also important to dry the glass thoroughly after washing. Any water in the glass can prevent excitement of the gas by covering designs set in the bottom of the glass, thus making the beer flat.
Conversely, some styles such as Belgian witbier benefit from being poured into a wet glass in order to control the often profusive head.
Formation of 'Nitrogen head'
The creamy head on beers such as
GuinnessGuinness is a popular dry stout that originated in the brewery of Arthur Guinness at St. James's Gate, Dublin. Guinness is based on the porter style that originated in London in the early 18th century and is one of the most successful beer brands worldwide. A distinctive feature is the burnt...
is created by a
widgetA widget is a device placed in a container of beer to manage the characteristics of the beer's head. The original widget was patented in Ireland by Guinness. The "floating widget" is found in cans of beer as a hollow sphere, 3 cm in diameter .-Background:Draught Guinness, as it is known today, was...
in cans or bottles using
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
, or by the process of drawing keg beer from a keg using nitrogen or mixed gas (carbon dioxide and nitrogen). 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.
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