What off-flavor is caused by oxidation in beer?

Oxidation in beer primarily leads to a flavor that is often described as papery or resembling wet cardboard. This off-flavor occurs when oxygen interacts with the compounds in the beer, resulting in the degradation of the hop flavors and fresh aromas that are typically desired. The chemical processes involved in oxidation can alter the beer's aromatic compounds, leading to the formation of stale or cardboard-like flavors that detract from the overall drinkability of the beer. This is particularly noticeable in pale ales and IPAs, where hop character is essential. Additionally, the presence of oxidation can mask other flavors and aromas, making the beer seem flat or lifeless.

Other flavors listed, like buttery flavor, which is caused by diacetyl, and umami or sourness that may arise from different fermentation issues or ingredient characteristics, do not result specifically from oxidation. This makes papery or wet cardboard the distinctive and correct answer to the question regarding oxidation-induced off-flavors in beer.