Why is it important to rinse a glass before pouring beer into it?

Rinsing a glass before pouring beer serves several purposes that enhance the drinking experience, particularly in relation to head formation. When a glass is rinsed, it is typically cooled and moistened, which creates an optimal environment for the beer. A chilled glass helps maintain the overall temperature of the beer, ensuring it doesn't warm up too quickly once poured. Additionally, by wetting the inside of the glass, it helps in the maintenance of a good foam, or head, which is crucial for both the visual appeal and aroma retention of the beer. Proper head formation allows for the release of volatiles and aromatics, enhancing the overall flavor experience as well.

While the other options touch on certain aspects of beer serving, they do not capture the primary reasons for rinsing the glass in the context of head formation and temperature maintenance, thus making the choice related to cooling and wetting the glass the most relevant.