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unique patented technical features such as an automatic safety pressure release valve, which will operate if the internal pressure exceeds 5 bar, re- sealing once the pressure has dropped to 2 bar. The six month ingress of O 2 is stated as <170 ppb, and CO 2 loss of approximately 10%. Lightweight Containers claim su- perior O 2 protection through the use of additional scavenging material in the UniKeg. At time of publication, figures were not available for shelf-life and gas barrier properties, as the product is still very new to market and under- going independent long-term trials. In- terestingly, this product features dual wall construction, designed to give a more robust keg. Due to the active O 2 scavenging component these types of container have a maximum lifetime of around 600 days from the date of preform manufacture, which is important to keep in mind when stock planning. The many advantages of this type of keg are discussed elsewhere in this issue. Coatings Barrier properties can be vastly improved by depositing a coating on the stretch-blown PET container. The coating material is usually amor- phous carbon or silicon oxide, which is applied to the internal surface with an acetylene plasma in a vacuum. To avoid cracking and flaking due to deformation of the flexible container, the coating needs to be extremely thin; just 60 to 150nm. Even so, these barriers provide excellent protection against O 2 ingress and CO 2 egress due to the intrinsically impervious nature of these materials. Very little barrier material is re- quired per container, approximately 0.04% by weight. However, additional capital investment is required for the coating plant, which must be placed inline after the preforms have passed through the stretch blow molder. Sidel’s ACTIS TM technology applies an amorphous carbon nano-coating in a high speed process of up to 44,000bph. Sidel states that a treated 330ml PET beer bottle has a shelf- life of six months, with an O 2 ingress of 1ppm and a loss in CO 2 of 10%. The Plasmax coating system, pro- duced by KHS, forms a 100nm silicon oxide layer on the inner surface. Throughputs of up to 46,000bph are possible, and integrated stretch blow molders/coaters are available. The
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1. Vacuum is created inside and outside the bottle (p1 = 0.08 mbar, p2 = 50 mbar) 2. Acetylene is injected into the bottle 3 and 4. Microwave energy causes acetylene to reach its plasma state 5. Amorphous carbon is deposited on the inner wall of the bottle 6. Bottle and treatment station are returned to atmospheric pressure (p0 = 1 mbar)
Sidel’s ACTIS TM plasma coating process
Closing comments PET offers many attractive benefits to the brewer, as a low-cost, lightweight and flexible container. It is being put to good use in the one-way keg sector and has made good progress in some of the markets for bottled beer. Young- er generations of drinkers would seem to be more accepting of beer packaged in PET, having being accustomed to all types of produce being packaged in plastic their whole lives. Continual advances in barrier technology, especially those incorpo- rating active and intelligent elements, may further increase the appeal of PET bottles. As they become able to dem- onstrate the freshness of the product directly to the customer at point of sale, this technology could become an essential tool for both the producer and the consumer. References and further reading Bamforth, C. W. and Krochta, J. M., (2010) ‘Packaging and the Shelf Life of Beer’ in Robertson, G. L., Food Packaging and Shelf Life: A Practical Guide , CRC Press. Bamforth, C. W., (2011) ‘125th Anniversary Review: The Non-Biological Instability of Beer’, Journal of the Institute of Brewing, 117(4), 488-497. Briggs, D. E., (2004) Brewing : Science and Practice, Woodhead. Lange, J., Wyser, Y., (2003) Recent Innova- tions in Barrier Technologies for Plastic Packaging – a Review. Packaging Technol- ogy and Science, 16, 149-158. Acknowledgements The author would like to thank the following for their kind assistance in producing this article. Clare Ander- son (for Petainer), Paul Box (Dolium), Rudolf Brouwer (Lightweight Contain- ers), Herman Standaert (Ecodraft) and Chris Twigger (for Sidel).
technology, which is marketed under the FreshSafe PET brand, results in a beer bottle with a six-month shelf life. By removing the silicon oxide layer, using an alkaline chemical process, 100% bottle-to-bottle recy- cling can be achieved, it is claimed. Future developments With many of the quality consid- erations having been already ad- dressed, educating the consumer about the benefits of PET will be key to it finding greater acceptance in the beer sector. Many of the mis- conceptions that are held regarding PET are perhaps based on exposure to budget-priced products, where quality and freshness were not the primary considerations. As the pro- portion of people who have only ever known PET as the major container used for soft drinks increases, much of the dogma surrounding PET may disappear. Intelligent packaging systems, which are continually growing in use in the wider food industry, may aid in the growing acceptance of PET by adding a distinct advantage to the format. At a basic level, these systems can give information to the consumer about the conditions to which the package has been exposed within the supply chain. This might be in the form of a colour-changing component which will indicate if the produce has been exposed to prolonged higher temperatures, for instance. Future technology that is able to demonstrate to the customer the freshness of a product, based on quality parameters such as O 2 and CO 2 concentrations, for example, will, undoubtedly, have a great influence on their purchases.
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