Beer head
From Wikipedia, the free encyclopedia
The foam on top of beer is called a head. It is caused by bubbles of carbon dioxide rising to the surface. The carbon dioxide may be produced naturally by the activity of the brewers yeast, or artificially by dissolving carbon dioxide under pressure into the liquid. The density and longevity of the head will be determined by the type of starch from which the beer was fermented. Wheat starch tends to produce larger and longer lasting heads than barley starch.
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[edit] Description
It consists of foamy bubbles. It is called a head because it is at the top of the beer. The head on beer is sometimes very small, although on some beers it is large, and is large enough, sometimes, to overflow from the beer glass.
[edit] Causes
The foam on top of beer is caused by the carbonation created by the carbon dioxide made by the activity of brewer's yeast. 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.
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.
This process yields the "fizz" and the head to beer.
[edit] Rinsing the glass
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. Also it is important to make sure the glass is well dried after washing. If there is water in the glass it 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.
[edit] Forced carbonation
The carbonation in filtered beers is created by injecting carbon dioxide artificially into the beer.
[edit] Nitrogen head
The creamy head on beers such as Guinness is created by a widget. It can also be created by a rocket widget in bottled Guinness.
