Napoleon, who said that an army marches on its stomach, took great care to feed his soldiers well. He could not always get fresh food for his men, and when he became interested in finding new methods of preserving food, he offered a prize for new ideas. It was won by a French chef, Francois Appet.
Appet' s idea of how to preserve meat was to cook it in a glass jar with a lid. The lid was not completely tight during the cooking, but just loose enough to allow the steam and hot air to escape. The cooking sterilised the meat- that is, it killed the micro-organisms. A lot of the air escaped from the jar, because air expands when it is hot. While the glass jar was still hot, he tightened the lid. The little air remaining inside contracted as the jar became cooler, and made a near vacuum.
Because the meat was cooked, and because there was very little air now inside the jar, the micro-organisms developed much more slowly and the meat remained sterilised. That, at least, was the theory, although Francois Appet was not very successful in practice. His method, however, was tried with different foods later in the nineteenth century. It became the standard method of bottling fruit, practised by housewives in many different countries, and from this idea the large canning industry developed.
The canning industry uses tin cans instead of glass jars. (These are usually called CANS in America and either CANS or TINS in Britain.) These cans are made from a thin sheet of steel coated with a protective layer of tin. This material is not only light and strong, but it is also very cheap. The food is put into the can and heated. This sterilises it. Killing most of the micro-organisms. The change in the food caused by the cooking and the lack of air inside the can prevent new micro-organisms from growing. There is not a complete vacuum( that is, complete absence of air) inside the can, because a little air remains. Nevertheless, this method of storing food is often called vacuum storage.