There are two basic methods of canning: water bath canning and pressure canning. Water bath canning requires no special equipment and is a good method for preserving fruits and foods with a high acidity, such as tomatoes and pickled products. Pressure canning is better suited for foods that have a low or neutral acidity, meats, and prepared foods.
To preserve food using a water bath canner, you will need glass jars, lids, rings, and a large pot of boiling water. There are special pots available specifically for water bath canning that have a removable rack for inserting and removing jars from the boiling water. The jars used should be made of glass and sterilized prior to use. The lids should be heated in very hot water until the glue softens to ensure a good seal.
Whatever food you are planning to can should be prepared (peeled, cut, etc.) and a packing liquid should be heated to the boiling point. The prepared food is then placed into the sterile jars, and the jars are filled with the hot packing liquid. Use the back of a spoon to remove any air bubbles and add more packing liquid if necessary. The jars should be filled to approximately ?" of the top of the jar, which is usually where the lid threads begin.
Once the jars are filled, carefully wipe the rims with a clean cloth, and place a lid on top of each jar. Use the lid rings to hand-tighten the lids down on the jars. Place the jars into the boiling water bath and begin timing once the water returns to a boil. The time that you will need to boil (or process) the jars depends on the type of food you are preserving. The recipe you use will have this information.
When the jars have boiled for the amount of time listed in your recipe, remove the jars from the canner with tongs. Place them on a towel in a location free of drafts and temperature changes and allow them to rest for 12 hours or until cool. You may hear popping sounds during this time as the lids seal.
Pressure canning is similar to water bath canning, in that you pack the jars in the same method. However, instead of placing them into a pot of hot water, you place them into a pressure canner. Once the canner is pressurized (you will hear the pressure gauge jiggle), begin timing. It is important that you use the right amount of pressure for the type of food you are trying to preserve, otherwise spoilage can occur.
Once the jars have cooked for the time listed on your recipe, turn the heat off under the canner. Allow it to rest undisturbed while it cools. Once the canner is cool and you can safely remove the lid, remove the jars to a place where they can cool undisturbed.
Whether or not you've used the water bath method or the pressure method, you'll want to check the seal of your jars once they have cooled. To do this, simply press one fining in the center of the lid. If you hear a popping sound, the jars have not sealed. Discard the contents immediately. If there is no popping sound, the jars have sealed and are safe to be stored. At this time you may also remove the ring, though many people choose not to so they don't lose them. Write the contents and date on the jar. Feel free to write directly on the lids, as you will discard those after opening the jar.