Food canning is helpful for those who have a garden or farm, because you can grow your own food and preserve it so you can store it for winter, drought or emergencies when you are able to harvest less crops. When you properly can foods, the container will be airtight to prevent spoilage. Depending on the type of food, you can keep it stored for differing lengths of time, typically, from a year to decades.

You are able to can fruits, jams, jellies, pickles and other preserves -- along with certain types of tomatoes -- using a boiling water bath method. This is the basic, commonly used method because of its lack of safety risk. Because these foods are highly acidic with a pH of 4.0 or less, Clostridium botulinum spores cannot exist when canned using this method. You can also perform this method without the use of a special pot like a pressure canner. You must add lemon juice or citric acid to certain foods that have a pH between 4.0 and 4.6 like certain tomatoes and figs.

You can preserve condiments such as relish, pickles, chutneys, sauces and vinegars using the boiling water bath method, because they contain vinegars, which raise their acidity levels to a safe point free of the risk of botulism, which is caused by Clostridium botulinum spores.

Vegetables, meats, poultry and seafood contain a low amount of acid, so further caution is needed to preserve them in a manner that is free of Clostridium botulinum spores and creates a product that is safe to eat, states FreshPreserving.com. This can be done with a home canning method of using a pressure canner, not the boiling water bath method. A pressure canner has a pressure gauge and a special locking mechanism between the lid and container, similar to a pressure cooker. There is a vent pipe at the top of the lid to allow steam to escape. The contents of the pressure canner must can reach a certain pressure to be effective, which depends on your altitude and the recommendations in the canner's manual. Generally the temperature should reach at least 240 degrees F for a certain amount of time, which depends on the food type and altitude, according to Canning-Food-Recipes.com.

If you have foods that have low-acidic foods, such as vegetables, meats, poultry and seafood, mixed with highly acidic foods such as fruits, you must can them as if they were low-acidic foods. They must be canned using a pressure canner.