What is a common topping for a glass of beer?

A head of foam is a common topping for a glass of beer because it enhances the overall drinking experience by contributing to the beer's aroma and appearance. The foam, often referred to as the "head," is created when the beer is poured and carbon dioxide bubbles rise to the surface, forming a creamy layer. This head can indicate the freshness and quality of the beer, and certain styles, especially ales, are known for their thicker foam. A good head of foam can also help to trap aromatic compounds, allowing the drinker to enjoy the full spectrum of the beer's flavors.

In contrast, a slice of lemon is typically associated with certain cocktails or wheat beers but is not a standard topping for all beer types. A sprig of mint is more commonly found in cocktails rather than beer, and a splash of soda is usually not added to beer unless it's a mixed drink. Therefore, the presence of a robust head of foam is a widely recognized and essential characteristic of a well-served beer.