The length of time beer lasts in a keg depends on various factors, including whether the keg is sealed or tapped, how it's stored, the type of beer inside, and the dispensing system used. An unopened keg that has been correctly stored—ideally in a refrigerator at a temperature between 3°C and 5°C (or 37°F to 41°F)—can stay fresh for two to six months. The exact shelf life varies depending on whether the beers are pasteurized or unpasteurized. Most commercial beers are pasteurized and can last up to 6 months refrigerated. Unpasteurized beers, often produced by craft breweries, are more sensitive and usually last six to eight weeks under the same conditions.

Once a keg has been tapped, its freshness leans on on how it’s dispensed. If you're using a CO₂ system, such as in a kegerator or bar setup, the beer can remain fresh for 4 to 8 weeks after tapping. The CO₂ prevents oxygen from entering into the keg, preserving carbonation and flavor. However, if the keg is tapped with a manual hand pump, often used at parties, air is introduced into the keg, which speeds up oxidation. In this case, the beer should be consumed within eight to twelve hours to avoid a stale or sour taste.

Systems like PerfectDraft, which use sealed and chilled six-liter kegs, can keep beer fresh for up to 30 days after opening due to their controlled, pressurized environment.

No matter the system, key factors that affect beer freshness involve temperature control, clean dispensing equipment, and limiting exposure to oxygen. Signs that beer is no longer fresh include a flat taste, sour aroma, or unusual cloudiness. With the right setup and storage, kegs of beer can stay enjoyable for weeks or even months.

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