Scientists develop milk cap with sensor that detects spoilage

Scientists from the University of California (UC) Berkeley and Taiwan’s National Chiao Tung University have created a wireless “smart cap” for milk cartons that is capable of detecting spoilage before the milk poured.

The closure is fitted with a capacitor and an inductor to form a resonant circuit and, when the carton is turned upside down, a small amount of milk is trapped in the cap’s capacitor gap. The circuit is then able to wirelessly detect changes in electrical signal that accompany increased levels of bacteria, and found that after 36 hours of the milk standing unopened at room temperature, the peak vibration frequency of the milk had dropped by 4.3%. During the same time, a refrigerated carton of milk would shift by around 0.12%.

The most surprising part of the experiment is that the closure – complete with electrical components such as resistors, inductors, capacitors and wireless sensors – was entirely 3D printed, meaning that the technology may one day be cost-effective enough to offer viable real-world applications.

The scientists have written their findings up in a report.

Liwei Lin, a professor of mechanical engineering at UC Berkeley and senior author on this research project, said: “Our paper describes the first demonstration of 3D printing for working basic electrical components, as well as a working wireless sensor. One day, people may simply download 3D printing files from the Internet with customised shapes and colours and print out useful devices at home.”

“This 3D printing technology could eventually make electronic circuits cheap enough to be added to packaging to provide food safety alerts for consumers. You could imagine a scenario where you can use your cellphone to check the freshness of food while it’s still on the store shelves.”