Practising proper food hygiene and safety techniques will help you prevent foodborne illness. Although not a perfect test, the senses are often the most reliable tools to tell if bacon is spoiled. Some common traits of spoiled bacon are opaque, slimy meat and a sour smell. The colour of the red meat will start to change to a greyish-brown colour when it is spoiling. Of course, there are certain health risks associated with spoiled food, so always remember to practice food safety and enjoy your food before its shelf life has expired.