Stackburn is a quality defect in canned foods caused by stacking freshly processed, still-hot cans before they have cooled properly. The trapped heat keeps the centre cans warm for hours, which can soften textures, dull colours, darken the product, and encourage chemical changes such as excessive Maillard browning or interactions between the food and the can lining. In severe cases the prolonged warmth can allow heat-resistant spoilage organisms to grow. Canneries prevent stackburn by cooling cans rapidly after retorting — usually with chlorinated water — and by spacing cases or using forced-air cooling so heat escapes before pallets are built. It is a classic example of why the cooling stage matters as much as the heating stage in canning.