Beer head

Beer head (also head or collar), is the frothy foam on top of beer which is produced by bubbles of gas, typically carbon dioxide, rising to the surface. The elements that produce the head are wort protein, yeast and hop residue. The carbon dioxide that forms the bubbles in the head is produced during fermentation. The carbonation can occur before or after bottling the beer. If the beer continues fermenting in the bottle, then it naturally carbonates and the head is formed upon opening and/or pouring the beer. If the beer is pasteurized or filtered then the beer must be force carbonated using pressurized gas.

The density and longevity of the head will be determined by the type of malt and adjunct from which the beer was fermented. Different mash schedules and cereal sources influence head retention. In general, wheat tends to produce larger and longer-lasting heads than barley.

Consumers tend to place a lot of importance on beer heads: too much of a head is undesirable because it detracts from the mass of the drink (similar to carbonated soda drinks), on the other hand a poured beer is viewed as incomplete unless it has the specific form of head expected for the type of beer. Some view the head on a beer as important because it helps provide the aroma of the beer. Another opinion is that it is important for the aesthetic look of the beer. The commercial significance of the head has led to academic studies.

At least one study suggests that the head assists in transport of beer after pouring by damping oscillation (sloshing) and converting vertical movement into horizontal movement.

The carbon dioxide may be produced naturally through the activity of brewers yeast, or artificially by dissolving carbon dioxide under pressure into the liquid. 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.

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