Using thermochromic ink, jars of Hellmann's mayo show people if their fridge is running warm

As part of Food Waste Action Week, Hellmann's is testing new labels for its jars of mayonnaise. Printed with thermochromic ink, which changes color based on temperature, the labels indicate whether a fridge is cool enough to keep food fresh.

Prototype jars were sent to Hellmann's fans, food waste campaigners and influencers in the UK last week to raise awareness about food waste. The labels feature a colorful design by illustrator Ellen Porteus, with a hidden layer that only appears below 5°C.

The Unilever brand explains that some foods can last up to 3 days longer in a fridge set below 5°C (versus 7°C). According to climate action campaigner WRAP, the average refrigerator in the UK is set at least 2°C too warm. No word yet on whether Hellmann's will extend its trial into a full rollout in supermarkets.