Beer is at its best on the day the keg is filled at the brewery. As days go by, the freshness reduces. With carbon dioxide and the proper temperature & pressure, a keg of beer can remain fresh for 45-60 days if non-pasteurized and 90-120 days if pasteurized. Beer will only remain fresh for 8-12 hours if dispensing the keg with air, i.e. ‘party pump,’ because air contains oxygen and oxygen drastically shortens beer’s freshness. Finally, due to administrative issues such as transit, warehousing, and distributor & retail delivery, a keg’s freshness life could lose 5-20 days.