Juice and milk safely packaged in returnable PET

Returnable PET: too good for niche applications

Whether it’s legal requirements, self-imposed climate targets or rising levels of eco-awareness among consumers: The aspect of sustainability is gaining more and more importance when it comes to choosing a packaging. “Which type of packaging scores highest against ecological criteria depends on a large number of factors and must be assessed afresh for each individual application,” explains Martina Birk, the officer responsible for the enviro sustainability program at Krones. But what is noteworthy in this context is that returnable PET containers are often not even considered. “But they do in fact boast an extremely attractive ecological footprint, especially when they are distributed mainly in the region where the drink is produced,” emphasises Martina Birk.

Bottle samples and cleaning processes tested

Krones and Alpla joined forces to harness these advantages for a broad range of beverages. “Returnable PET containers have so far been used primarily for carbonated soft drinks and water,” explains Jörg Schwärzler, a returnables expert and project manager at Alpla. “ But we were quite sure that if we were to synergise our expertise in the fields of materials science, preform design, container design and systems engineering, we’d also find a suitable solution for sensitive beverages likes juices or dairy products. A 38-millimetre neck finish offers special advantages for sensitive returnable-container applications.”

The partners devoted special attention to the container cleaning process because “PET is less resistant to heat than glass”, explains Ines Bradshaw, a developer at Krones. “This is why we had to find a way to ensure high levels of microbiological safety and a large number of turnarounds even with lower cleaning temperatures.”

To collect an objective and meaningfully informative data basis, the Krones pilot plant for cleaning technology in Flensburg ran an extensive series of tests, in which the interaction of various bottle samples and cleaning processes was analysed. “The tests presented a very clear picture of the thermal, chemical and mechanical factors influencing the overall result,” says Bradshaw. “It turned out that with appropriate parameter selection – especially in regard to caustic concentration, temperature, additive and mechanical impact – temperatures of around 60 °C are sufficient for reliably removing even dried-on protein, grease and starch soiling from the containers.”

It proved impossible to distinguish returnable PET bottles after as much as 25 turnarounds from new containers in terms of microbiology. Ines BradshawDeveloper at Krones

Direct comparison with returnable glass

A direct comparison of returnable PET and returnable glass revealed yet another interesting fact: As the containers passed through more and more cleaning cycles, the alkaline cleaning medium made the glass bottles’ surfaces ever rougher whereas nothing comparable was noticed for the PET containers. “For filling sensitive beverages, especially, a consistent container quality may be a benefit that’s not to be underestimated,” says Ines Bradshaw. 

To obtain final certainty in regard to safety, microbiological tests are currently ongoing, with some first results already available. They validate what had already been observed so far: “It proved impossible to distinguish returnable PET bottles after as much as 25 turnarounds from new containers in terms of microbiology,” says a gratified Ines Bradshaw. Now that feasibility has been confirmed, the project has reached an important milestone – and is ready for the next big step: Preparations for technical field testing are now in full swing.