Foam is the result of CO2 bubbles rising through the beer. These bubbles attach themselves to substances in the beer and form a skin around the bubble. Obviously the more CO2, the more bubbles, but the goal of the brewer is not bubbles but stability of the head. As foam collapses, evaporating bubbles tend to solidify the beer near the surface, allowing more beer to be poured with less foaming after a few minutes have passed.
Head stability depends on the presence of substances with low surface tension in the beer which can form stable elastic bubbles. The two primary contributors to head retention are certain high molecular weight proteins and isohumulones (alpha acids from hops). Therefore beers with more proteins that are highly hopped will have higher head retention.
Methods for Improving Head Retention
· The use of body and head enhancing malts such as crystal, wheat, or carafoam
· The altering of the mash schedule to enhance head retaining proteins
· The use of heading agents – additives that enhance head retention
· Addition of high alpha hops – which will increase bitterness, but also increas isohumulones that enhance head retention
· Limiting the use of household soaps on drinking glasses and homebrew equipment