Topics discussed in this paper include the advantages and disadvantages of plastic (especially PET) bottles compared to other containers for beer, the volumetric filling technology used in the Krones "VODM-L-PET" long tube PET beer bottle filler (which also features a "ring kettle" carbon dioxide flushing system for expelling air from the bottles and a separate gas supply pipe which then fills the bottles with fresh, pure carbon dioxide before they are filled with beer, as well as springless valves for better hygiene), the influence of the closure type on the susceptibility of PET bottled beer to oxidative deterioration (and other advantages and disadvantages of the most common closure types, namely plastic and aluminium screw caps, crowns and ring pull caps), the need for an inner cap under the main closure (especially if the latter is a plastic screw cap) to minimize the amount of air that can be trapped in the headspace during capping and the effect of the length of the filling tube (long tubes which reach almost to the bottom of the bottle generally achieve more efficient gas flushing, requiring less carbon dioxide to expel the air completely). In general, even the best filling machines and closures available at the time of writing still leave PET bottled beer with a much higher total package oxygen (TPO) content than beer in a glass bottle of the same capacity, but there is still significant scope for variation in the TPO content of PET bottled beer because of the influences of the factors mentioned above. It is also noted that the oxygen concentration per unit of volume is lower (other things being equal) in PET bottles of larger capacity because the larger the bottle, the smaller the headspace relative to the liquid volume.
