The period of time that beer remains fresh depends on the dispensing method; beer dispensed with CO2 can remain fresh for up to 120 days, while beer dispensed with an air pump is fresh for up to 12 hours. Pasteurized beer dispensed using CO2 lasts the longest.
As with beer in bottles, beer in kegs is best to consume the moment it is put into a container. Non-pasteurized beer usually has a shelf life of up to 60 days, but allowances have to be made for shipment, which can take up to 10 days, and retail delivery, which can take up 20 days. It is safe to assume that non-pasteurized beer has a shelf life of about 30 days and pasteurized beer has a shelf life of about 90 days. Party pumps dispense keg beer using air, which has an adverse affect on beer, causing it to go flat in less than a day.