As an expert sommelier and brewer, I can confidently say that a keg will indeed go bad without CO2. When a keg is tapped, it is typically pressurized with carbon dioxide (CO2) to maintain the freshness and carbonation of the beer. However, if a picnic pump is used instead, which relies on oxygen instead of CO2, the beer will not last as long and will eventually go flat and spoil.
The main reason for this is that oxygen is a reactive gas, and when it comes in contact with beer, it can cause oxidation. Oxidation is the process where oxygen reacts with the compounds in the beer, leading to the deterioration of flavors and aromas. This can result in off-flavors such as cardboard or stale notes, giving the beer a less enjoyable taste.
Additionally, oxygen can also promote the growth of bacteria and other microorganisms in the beer. This can cause the beer to spoil more quickly, leading to a shorter shelf life. Without the protective barrier of CO2, these microorganisms can thrive and multiply, further degrading the quality of the beer.
The rate at which a keg will go bad without CO2 depends on several factors, including the type of beer and the amount of oxygen pumped into the keg. Generally, lighter beers with lower alcohol content and less hop presence will spoil more quickly compared to heavier, high-alcohol beers or beers with strong hop profiles.
In my personal experience, I have witnessed the unfortunate consequences of a keg going bad without CO2. During a backyard party, a keg was tapped using a picnic pump, and despite efforts to consume the beer within a reasonable time frame, it went flat and developed off-flavors within just a few hours. The once-refreshing and carbonated beer turned into a disappointing beverage that nobody wanted to drink.
To summarize, a keg will go bad without CO2 due to the reactive nature of oxygen and its ability to cause oxidation and promote bacterial growth in beer. The use of a picnic pump, which relies on oxygen instead of CO2, accelerates this process, resulting in flat, spoiled beer within a relatively short time frame of about 12-24 hours. It is crucial to finish the keg within this time frame to enjoy the beer at its best quality.