Expiration dates on food reflect the range of time when products are at their best nutritional value. To prevent consuming spoiled products, many consumers throw food away after the expiration dates. However, these dates are not an accurate indicator of spoilage, and this ambiguity adds to the food waste problem. To mitigate this, we developed a paper-based biosensor that consumers can use at home to assess their milk for spoilage. Our device detects the quorum-sensing molecules, acyl-homoserine lactone (AHL), produced by spoilage bacteria, both of which increase in concentration as spoilage progresses. Our detection system visualizes high AHL levels with the expression of pigment proteins. Additionally, to ensure food safety, a cell-free system was implemented such that no live genetically-engineered bacteria will be introduced to the consumer product.