When canning was invented, no one knew why food packed and heated inside containers remained fresh for a long time.

When canning was invented, no one knew why food packed and heated inside containers remained fresh for a long time.

Then, in 1860, French scientist Louis Pasteur discovered that food spoilage was due to bacteria present in all fresh food and in the air. These organisms break down substances in the food and make them useless or harmful to people.

With canning the heating of the food kills bacteria and the sealing of the can prevents more bacteria from getting into the food. Food inside a can should stay fresh for as long as the tin remains unopened.

In the 1920s American companies found that packing food in liquid kept it fresher and more nutritious.

That's why most canned foods are packed in water. And all cans today are vacuum-packed, which means that the air is sucked out of the can before it is sealed. This prevents bacteria in the air from infecting the food - bigsiteofamazingfacts.com; foodreference.com; wikipedia.org