A little history for you. . . I was looking at stuff on the net and I looked up the word "canning" and came up with the Wikipedia article below.
Make sure you at least read the FIRST paragraph. It mentioned some canned food over 100 years old; it was still edible and not poisonous, though not the most nutritious or tasty.
And here are a couple more on-line articles for some more history:
Canning/Food Processing at Britannica.com
Finally, here is a .pdf article on recommended methods of Canning and some info on some methods to avoid:
Methods of Canning from the Agricultural Extension Service of the Univerisity of Tennessee