As an expert sommelier and brewer, I can provide you with a detailed answer to the question of how long keg beer lasts once it's been opened.
Once a keg of beer has been tapped and exposed to oxygen, the clock starts ticking on its freshness and quality. The presence of oxygen in the keg accelerates the oxidation process, which can cause the beer to go flat and develop off-flavors relatively quickly.
The duration for which keg beer remains drinkable after it has been opened can vary depending on several factors. The type of beer, the amount of oxygen that has entered the keg, and the conditions in which it is stored all play a role in determining its shelf life.
Typically, a tapped keg of beer will last anywhere from 12 to 24 hours before it starts to degrade in taste and quality. This timeframe is a general guideline and can vary depending on the specific beer and circumstances.
It's important to note that some beer styles are more susceptible to oxidation and spoilage than others. Lighter, more delicate beers such as lagers and pilsners tend to lose their carbonation and flavor faster when exposed to oxygen. On the other hand, stronger and more robust beer styles like stouts and porters may be able to hold up slightly longer.
Additionally, the amount of oxygen that gets pumped into the keg during the tapping process can impact its shelf life. If excessive amounts of oxygen enter the keg, the beer will oxidize at a faster rate, leading to a shorter lifespan. This is why it's crucial to ensure proper tapping techniques and minimize oxygen exposure as much as possible.
The storage conditions of the keg also play a significant role in its longevity. Ideally, kegs should be stored in a cool and dark place to slow down the oxidation process. Exposure to heat and sunlight can accelerate the degradation of the beer, leading to a shorter shelf life.
It's worth mentioning that while a keg of beer may still be technically drinkable even after the recommended timeframe, the quality and taste will likely be compromised. The beer may become flat, lose its carbonation, and develop off-flavors as a result of oxidation.
In my personal experience, I have encountered situations where keg beer has been left open for longer periods, and while it may still be consumed, the difference in taste and quality is noticeable. The beer loses its freshness, and the flavors become muted or altered due to oxidation.
To summarize, once a keg of beer has been opened and exposed to oxygen, it typically has a shelf life of 12 to 24 hours, depending on the beer style, oxygen exposure, and storage conditions. It's best to consume the beer within this timeframe to enjoy it at its best.