Today in 2010, US Patent 7810679 B2 was issued, an invention of Albert W. Wauters, Ian Anderson, and Edward P. Duffy, assigned to Anheuser-Busch Inbev S.A., for their “Beer Dispensing System with Gas Pressure Reservoir.” Here’s the Abstract:

A home beer dispensing apparatus has a keg having a self-contained bag filled with a beer and a pressure system. The pressure system creates a pressurized air space between the keg inner walls and the bag to assist in the dispensing of the beer. The pressure system has a keg one-way air valve mounted to a top wall of the keg to permit entry of pressurized air into the keg. The pressure system has a pressure reservoir mounted in the dispensing apparatus outside the keg and in fluid flow communication with the keg one-way valve. The reservoir stores a charge of pressurized air and supplies at least a portion of this charge to the keg through the keg air valve when the dispensing apparatus is operated to dispense the beer. The reservoir provides a reserved charge of pressurized gas that is on hand to reduce dampening pressure fluctuations during beer dispensing which can result in beer frothing, especially during the early stages of beer dispensing when the air head space in the keg is small. Further, the apparatus may also have a pressure sensing system adapted to measure time rate of pressure change in the keg. The apparatus has a signaling device responsive to the time rate of pressure change in the keg to produce a signal related to volume of beer remaining in the bag. Preferably, the signal is displayed visually on the dispensing apparatus.