PETpla.net Insider 06 / 2012

BEVERAGE PREPARATION 28 PET planet insider Vol. 13 No. 06/12 www.petpla.net sensitive BEVERAGES BEVERAGE PREPARA The trend toward PET packaging on the non-alcoholic soft drink market has been holding strong for years. The market share of disposable PET packaging was only 1.9% in 1999, but in 2004 it had reached 30.9% and by 2011 it had grown to 71.5%. In the course of this development, the weight of the bottle has fallen significantly. One of the distinctive properties of PET bottles is permeability. The extent to which atmospheric oxygen permeates the bottle can be critical, since in addition to temperature and light, oxygen is one of the main fac- tors which contributes to the ageing process of foods. Permeability rises in inverse correlation to the weight of PET bottles falling: the thinner the packaging, the greater its permeability. Bottle weight and permeability This article discusses an experiment using P.E.T.proof to compare seven bottles with varying physical proper- ties. This demonstrates the influence that the bottle weight and, by extension, the thickness have on permeability and subsequently on a beverage’s sensory stability. To date, the industry has had to add greater amounts of ascorbic acid as an antioxidant to bind the amount of oxygen which penetrates packag- ing. However, test results indicate that additional ascorbic acid cannot always compensate for the sensory changes a product undergoes during its shelf- life. The use of oxygen scavengers can offset, if not overcompensate for, the consequence of lowering the weight of the bottle. Scavengers are substances or plastic systems which, when added to the PET compound, capture and oxidise the oxygen permeating the walls of the bottle. In the past several years, the weight of PET bottles has fallen dramatically: whereas a standard 0.5l bottle still weighed 27g in 2003, the figure fell to a mere 15.3g in 2007. The weight continued to fall to 12g by 2011. As a result, packaging has become thinner, and this in turn leads to higher gas permeability. (Fig. 1) P.E.T. proof provides a realistic sim- ulation of oxygen permeation, thus per- mitting a comparison of the permeability rate of different bottle weights. In one test sequence, bottles weighing 19.8, 21 and 24g were compared. To rule out the effect of the cap, the mouths of the bottles were sealed with an aluminum foil. The oxygen permeation in the lightest bottle was 33% higher than in the heaviest. (Fig. 2) The 33% higher permeation rate accompanied by only 17.5% less material indicates that reducing the material does not have a linear effect. This can be explained as follows. The weight of the PET bottles was repeatedly reduced. However, if the overall reduction in material of the bottles which weighed a total of 19.8 or 24g is contrasted with the weight of each individual parts of the bottle, it becomes clear that the neck where the cap is screwed on remained at a con- stant weight of 6.15g. The weight is only lower in the body of the bottle, and cor- respondingly the material thickness was reduced there alone. This allowed the proportional weight to decline and thus the permeability of the body of the bottle to increase by 31% in the lighter bottle. In other words, reducing the amount of material is not a linear phenomenon: permeation increases disproportionately as weight falls. P.E.T. proof: Wild’s quick-test procedure Based on an article by Frank M. Spinner, Wild product development, Beverages Weighing up the PET permeability rate One of the distinctive properties of PET bottles is permeability. Conducting real-time tests in order to determine the impact that packaging has on bever- age quality takes a great deal of time. The process can take several months, which means it is no longer viable for today’s market needs. Wild’s quick-test procedure called P.E.T. proof simulates the effects of oxygen on beverages in PET bottles and provides robust data after a mere 21 days.