What gas is known to negatively affect a beer's flavor and aroma?

Oxygen is known to have a detrimental impact on a beer's flavor and aroma. When beer is exposed to oxygen, it can lead to oxidation, which creates off-flavors that can make the beer taste stale or cardboard-like. This process can also affect the hop character, resulting in a loss of freshness and vibrancy. Additionally, oxidation can alter the beer's aroma, leading to undesirable characteristics such as sherry-like notes.

While carbon dioxide and nitrogen are gases commonly used in the brewing and pouring process, they do not negatively affect flavor and aroma in the same way. Hydrogen sulfide, on the other hand, is a compound that can produce a rotten egg smell but is more of a brewing fault often related to yeast activity rather than a direct impact of oxygen exposure. Understanding the role of oxygen and its effects is crucial for maintaining beer quality.