After a beer has been introduced to air, how long does it remain drinkable?

Once a beer has been exposed to air, its freshness begins to degrade due to oxidation. While some beers, particularly more robust styles like certain IPAs or stouts, can hold up a bit better, most beers will start to lose their desirable flavors and aromas within a day.

The exposure to air can lead to off-flavors, with the beer becoming stale or developing undesirable characteristics. In general, beers like lagers and more delicate ales can become less palatable within a few hours of exposure. Therefore, the understanding that beer remains drinkable for less than one day accurately captures the rapid deterioration of flavor and overall quality once it has been introduced to air.

This timeframe makes it clear that while one might technically be able to drink beer that has been open for longer, the quality will have significantly diminished, which is an important aspect to consider when enjoying beer at its best.