Researchers at the Istituto Italiano di Tecnologia in Italy have designed a food-grade device from edible materials that indicates whether a frozen product has been thawed and refrozen.

The researchers’ work, titled “Self-Powered Edible Defrosting Sensor” was published in ACS Sensors, by Ivan Ilic, Mario Caironi, and their colleagues.

The device can detect defrosting events by coupling a temperature-activated galvanic cell with an ionochromic cell. All components of the sensor are made with entirely edible materials, including table salt, red cabbage, and beeswax.

The galvanic cell operates with an aqueous electrolyte solution, producing current only at temperatures above the solution’s freezing point. The ionochromic cell uses the current generated during the defrosting to release tin ions. This forms complexes with natural dyes, causing the color to change and providing information about defrosting events.

The temperature at which the sensor reacts can be tuned between 0 and −50 degrees Celsius. The temperature range allows the device to be used in the supply chain in several ways: as a sensor, it can measure the length of exposure to above-the-threshold temperatures, while as a detector, it can provide a signal that there was exposure to above-the-threshold temperatures.

According to the study, the device could ensure that frozen food is handled correctly and is safe for consumption. Furthermore, the sensor could be used by workers in the supply chain as well as consumers, ensuring that the food was properly frozen during the whole supply chain.