What this label does, as you can see, is change color over time. Once the meat (or other perishable product) is past it’s due, the label will have turned from white to blue, making the item unscannable. The label has one layer of info for the food with the barcode, and another on top with special ink reactive to ammonia. The ink is made of non-toxic, safe pigment of purple cabbages. A device for truly honest food store owners, but as a salvation for the problem of bad food being sold worldwide? Maybe not.
Reference:
http://www.yankodesign.com/2008/12/11/the-freshness-of-labels/
