What causes beer to have foam?

Foam in beer, also known as head, primarily results from the interaction of proteins present in the beer, which aggregate to form a colloid during certain conditions. These proteins come from the malted barley and are essential for creating stable bubbles when the beer is poured into a glass.

When beer is carbonated, it contains dissolved carbon dioxide, which gets released upon pouring or agitating the beer. The proteins stabilize these gas bubbles, creating foam as the carbon dioxide escapes and forms bubbles at the surface. The presence of proteins, including those derived from malt and yeast, is critical since they contribute to the surface tension necessary for bubble formation and stability of the foam.

The presence of hops does contribute to certain aromatic compounds and can impact the mouthfeel, but they do not directly cause foam. The fermentation process has its role in producing carbonation and flavor compounds, but it is not the direct cause of foam formation. Similarly, water’s mineral content can impact the beer's overall character and mouthfeel, yet it does not specifically influence the generation of foam. Participants in brewing and beer appreciation should recognize the importance of proteins and their behavior in foam stability for a deeper understanding of beer quality and serving.