Normally these systems were designed for short time periods of dispensing as they utilize high pressure to dispense correctly. This high CO2 pressure will over carbonate the beer if it is not consumed within hours. The only way to accomplish maintaining carbonation overtime is to vent excess pressure off before the keg is untapped. Turn shut off valve on regulator to off position. Pull relief valve on keg coupler while still in tapped position venting pressure. Reset regulator to approx 14 PSIG and open valve at regulator rejuvenating keg with correct pressure for storage. Then the product should be refrigerated at 38 degrees F. Particularly if it is a non-pasteurized beer. Good luck!
Scott Zuhse, Instructor
Micro Matic Dispense Institute