How are modern food cans sealed to make them airtight?

Modern food cans are made airtight through a process known as double seaming, which creates a hermetic seal.12

In this process, a machine places the lid onto the can body. The curl on the cover and the flange on the can body are rolled into position and then flattened together to form interlocking folds. To ensure the seal is completely airtight, a thin layer of polymer sealing compound is applied to the rim of the cover; during the seaming process, this compound is dispersed between the layers of metal.1

For traditional cans, this mechanical sealing is often preceded by an exhaust process—using steam or hot water—to drive out air, which creates a partial vacuum inside the container once it cools. Alternatively, some products are vacuum-packed using specialized machines that mechanically exhaust the air before sealing. In the case of aseptic canning, presterilized containers are filled and sealed within a sterile atmosphere using a sterile cover to maintain product integrity.31