Canning is the process of preserving food by sealing it in a tin, steel, or aluminum can, most of which are lined with a plastic-like film of bisphenol A or Bisphenol S and other chemicals. This term is also sometimes used in reference to preserving food in within a partial vacuum in any sealed container such as a canning jar. When food is canned, an effort is made to kill all bacteria and enzymes in the food first so that it will last for some time. For this reason, food is almost always blanched or cooked prior to canning. If this attempt is not successful, the food is likely to spoil, even in the partial vacuum of a can or jar.
Potential toxic substances that can migrate from the can into its contents include lead, causing lead poisoning, or Bisphenol A (BPA) a potential endocrine disruptor that is an ingredient in the epoxy commonly used to coat the inner surface of cans, or its replacement, Bisphenol S (BPS), which is also believed by some to be harmful, perhaps more so than BPA.