Canning is a great way to preserve food when it is at the peak of freshness. Keep in mind, though, that canning is like chemistry class in your kitchen. If not done properly, canning can be dangerous.
If you follow a scientifically-tested canning recipe, you will be able to safely enjoy your preserved food for up to one year. However, using an untested recipe can lead to a potentially dangerous chemistry experiment in your kitchen.
Canning is a continuously evolving science, and recommendations are updated as new information is released. Even though Grandma's recipe may be delicious, that does not mean it's safe. You can't always see, smell or taste the things that can make you sick, or even kill you.
If you are looking for a safe canning recipe, try visiting the National Center for Home Food Preservation. Here you can learn all about safe food preservation techniques.
For more information about why it is important to can safely, see Summer Garden Produce Brings Bounty of Food Preservation Questions, Concerns.