Essentials of Canning. The preservation of canned products requires hermetically sealed cans. The process of attaching a can end to a can body is called Double Seaming. The Double Seam is a metal to metal seal formed by mechanically interlocking five layers of metal together, 3 layers from the end & 2 layers from the body. The integrity of a seamed can is most vulnerable at the Double Seam and preventing leakage is imperative. As an example, for food cans with an internal vacuum, the Double Seams can leak and allow micro-organisms to be drawn into the can, potentially leading to Botulism and food poisoning. With Craft Brew and beverage products, a loss of gas or internal pressure due to a Double Seam defect may allow the introduction of air into the can, affect taste and reduce the shelf life of your product. Recognising seam defects and immediately correcting them protects your can and your product. If you are going to invest a lot of time and effort into making the best possible product, you need to be sure the consumer receives it the way you intended. The only way to ensure this happens is by maintaining Double Seam integrity.