Brazilian scientists have created a biodegradable sensor made from starch that changes color when moisture enters food packaging. The sensor uses cobalt chloride, a chemical that turns from blue to pink as moisture levels increase and back to blue as they decrease. This simple visual indicator allows consumers and manufacturers to check the quality and crispness of foods like cookies without needing specialized equipment. The research was conducted by scientists at the São Carlos Institute of Chemistry at the University of São Paulo (IQSC-USP) and published in the journal Food Chemistry in June. The team tested the sensor with cream crackers, which are highly sensitive to moisture and quickly lose their crisp texture when stored improperly. The results showed that the color change of the sensor closely matched the increase in moisture, which was linked to the loss of crispness in the crackers. The sensor, a small starch-based cylinder, changes color rapidly—shifting between shades of blue and pink—depending on the humidity in its environment. This happens because the cobalt chloride inside reacts to water vapor, altering its chemical structure and, consequently, its color. According to Bianca Maniglia, a professor at IQSC-USP and the research adviser, the unique aspect of this study was the sensor's large surface area, which makes it highly sensitive to different humidity levels inside packaging. "If I place it in a very dry environment, it responds. Conversely, if I place it in a very humid environment, it also responds," she explains. The inspiration for using cobalt chloride came from a childhood memory of a weather rooster, a common kitchen decoration in Brazil and Portugal during the 1980s. These ornaments changed color to predict whether it would rain or be sunny, and the researchers adapted the same principle for their sensor. The team is also working on integrating the sensor with cryogel, a highly porous material made by freezing polymers and then removing the water through a process called sublimation. This creates a structure that can interact effectively with the environment. However, the current version of the sensor is not yet safe for direct contact with food due to the presence of cobalt chloride, which is toxic. The research group is now exploring alternative materials, such as bioactive compounds from jabuticaba peel, a fruit native to Brazil. These natural pigments change color in response to pH changes and could be used to monitor the spoilage of meat. Additionally, they offer antioxidant benefits, which could add value to the compounds themselves. Further studies are needed before the technology can be used in commercial food packaging.