Japan meat labels show changing colors based on the level of ammonia the food emits as it ages. After it has passed its expiration date the barcode is no longer readable, making it impossible to sell.
Japanese design agency To-Genkyo proposed a dynamic freshness label for meat products. The hourglass-shaped label contains special ink that changes color based on the amount of ammonia emitted by the meat (the older the meat, the more ammonia it releases).
Over the last year or so Japan had been struck by a number of scandals involving food companies tampering with expiration dates. The new design keeps people honest by changing colors based on the level of ammonia the food emits as it ages.
Elegant detail: When the meat is no longer suitable for sale, the ink blocks the barcode at the bottom so that it cannot be scanned at the cash register.