What indicates the carbonation and freshness of beer?

The head produced when poured is a key indicator of beer's carbonation and freshness. When a beer is poured into a glass, the formation of the head—essentially the foam on top—occurs due to the release of carbon dioxide (CO2) that was dissolved in the beer. Fresh beer typically has a tight, stable foam head, indicating that there is an adequate level of carbonation and that the beer is still fresh.

A well-carbonated beer will produce an appropriate amount of head, contributing to the overall aroma and mouthfeel, enhancing the experience of the beer. If a beer has little to no head or a quickly dissipating foam, it can suggest issues such as being stale or improperly carbonated. Therefore, the presence, size, stability, and quality of the foam head serve as visual cues for both the carbonation level and freshness of the beer.