As an expert sommelier and brewer, I can tell you that the duration a tapped keg lasts without CO2 can vary depending on several factors. One crucial factor is the type of beer you have in the keg. Different styles of beer have different levels of carbonation, and this impacts how long the beer will stay fresh without CO2.
Typically, a tapped keg will last about 12-24 hours without CO2. However, it's important to note that this is just a general estimate, and the actual duration may vary based on various circumstances. For instance, if you have a highly carbonated beer like a wheat beer or a Belgian ale, it may lose its carbonation more quickly without CO2. On the other hand, a less carbonated beer like a stout or a porter may hold up a bit longer.
Another factor to consider is how much oxygen was pumped into the keg when it was tapped. Oxygen exposure is the main culprit when it comes to beer going flat or developing off-flavors. When you tap a keg without using CO2, oxygen gets introduced into the keg, and this can accelerate the deterioration of the beer.
To give you a more personal perspective, let me share an experience I had with a tapped keg without CO2. A few years ago, I attended a small outdoor gathering where we decided to have a keg of pale ale. Unfortunately, we didn't have access to CO2, so we had to rely solely on the picnic pump to dispense the beer.
Initially, the beer poured well, with a decent level of carbonation. However, as the hours went by, the beer started to lose its fizz and became increasingly flat. By the end of the evening, the beer had lost most of its carbonation, and the taste had become noticeably stale. It was a disappointment for everyone, as the beer wasn't as enjoyable as it would have been if we had used CO2 to maintain its freshness.
To summarize, a tapped keg without CO2 will typically last around 12-24 hours, depending on the beer style and the amount of oxygen introduced during tapping. It's essential to keep in mind that the absence of CO2 can result in the beer losing its carbonation and developing off-flavors more rapidly. If you're planning an event or gathering where you won't have access to CO2, it's best to consume the beer within a shorter timeframe to ensure the highest quality and taste.