US Patent 9915638 Bio-reactive food expiry label

A food expiry label includes a layer of material (such as a water-swollen mammalian gelatine) that undergoes a phase transition (such as from solid to liquid) upon exposure to bacteria or fungi that result in food spoilage. The label may incorporate a tactile surface that the user can feel underneath the layer of gelatine once the gelatine has changed from solid to liquid. Thus a user can detect when a foodstuff is likely to have spoiled or been on the shelf for a predetermined period simply by feeling the label.