All milk jugs are not created equal

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A new study recently published by researchers from Cal Poly San Luis Obispo contains some surprising environmental news for the dairy industry: The plastic container that milk comes in makes a difference in the carbon footprint of milk.

Researchers evaluated the carbon footprint of three different plastic milk jugs. The milk jugs studied were identified as “original,” the “cube” and the “stackable.” The “original” and the “cube” milk jugs need to be stacked in plastic crates for distribution. The plastic crates add an extra layer of materials. The “stackable” milk jug stacks on top of one-another, with the addition of a corrugated fiberboard sheet between layers. The “original” and the “cube” designs are more commonly found in the U.S. than the stackable design, which is currently being used by club stores such as Costco and Sam’s Club.

Results from this study were much different than researchers originally anticipated. “The ‘stackable’ milk jug markets itself as having a lower carbon footprint,” says Jay Singh, professor and packaging program director at Cal Poly San Luis Obispo. “When we started this research project, we thought the ‘stackable’ milk jug would have a slightly lower carbon footprint than the other milk jugs -- not as low as marketing claims, but still lower.”

But when the results came in, this was not the case. A detailed analysis by Singh and his researchers concluded that the “original” and the “cube” actually had a lower carbon footprint than the “stackable," despite the need for plastic crates to stack the milk jugs for shipment.

One reason was that the “stackable” containers require more plastic per unit in order to be “stackable.” This extra plastic contributes to greenhouse-gas emissions and energy consumption.

The plastic crates used for the “original” and the “cube” are maintained through a closed-loop system. When a new shipment of milk is dropped off, the plastic crates from the previous delivery are added to the returning truck shipment. The reusable crates experience 520 trips in an average service life, compared to 30 trips for the wooden crates used for “stackable” milk jugs. The grocery chain involved in this study can track its plastic milk crates back more than 30 years, explains Singh. He does note that the “stackable” milk jugs would come out better, if there were no closed-loop systems.

 “Our study does confirm that if it’s a closed-loop system, the ‘original’ and the ‘cube’ are the best milk jugs for the environment, up to a 250-mile radius,” he concludes.

The study was recently published in the Journal of Packaging Technology.

Read more on this study.



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