If you are unable to get an idea by smelling the milk, that whether the milk is gone bad or not. Scientists has recently invented Smart Lids, which will tell itself that the milk within the bottle is good or bad.
University of California in Barclay and National Chiao Tang University Taiwan, has invented such bottle lids, that will be able to identify you about the milk quality of perseveres. These lids contains 3D printed material, a Circuit and wireless sensors are able to identify once milk is touched by the lid, whether the milk is in good condition or it has been expired.
This lid helps to identify if there are any bacteria present within the liquid or any other changes occurring within the liquid. Once identified, it identifies any problem in a real-time. By this invention, now people can check the quality of milk through their Mobile phone application.
Scientists are still working on the technology, so it can be used in different other purposes and research is still underway.