False labeling on food is a worldwide concern. Many consumers carefully check the food labels. However, expiry dates typed on the labels in characters are easily faked and there is a limit for its reliability.

To solve such problem. we suggest a food label which changes its color by reacting to ammonia given off by food when it is becoming spoiled. When the food is no longer edible, the food label makes a bar code non-scannable and non-purchasable with pattern. This food label is reliable and difficult to counterfeit since it directly reflects freshness.

Via: http://www.packagingoftheworld.com/2010/06/fresh-label.html