Sales of unpasteurised beer in 'mini-kegs' of between 1 and 3 litre capacity have reached 3-4% of the Japanese beer market. 60% Of these 'mini-kegs' are made of polyethylene terephthalate (PET). An account is given of the experiences gained by Suntory, the Japanese market leaders, in the design, production and sale of beer in these containers. Beer in a PET container stored at not more than 15oC was considered to be equivalent in flavour stability to beer in a steel container after 8 weeks storage. The results of an investigation into oxygen permeability show that the surface to volume ratio of the container and wall thickness have a major influence on the igress of oxygen and on the loss of carbon dioxide on storage. Spherical PET containers were found to be preferable. Desorption and permeation models have been devised to explain the mechanism by which oxygen gains access to beer in PET containers. The influence of PVDL coatings on permeation is discussed. It is better for beer quality to fill PET containers as soon after their production as possible.
Keywords : beer bottle carbon dioxide container flavour oxygen plastic