<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2008) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2008) (Learn how and when to remove this template message) </Td> </Tr> <P> 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 . </P> <P> 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 . </P>

Where does the carbonation in beer come from