There are two safe ways of canning, depending on the type of food being canned. These are the pressure canning method and the boiling water bath method.
Pressure Canning Method:
Pressure canning is the only safe method of canning low-acid foods (those with a ph. of more than 4.6). Although high acid foods may be canned in either a pressure canner or boiling water bath, pressure canning is the only recommended method for canning low-acid foods. Low-acid foods include all vegetables, meats, poultry and seafood. This method is also necessary for canning such items as soups, stews and chili. Note: Although considered a fruit, tomatoes have a ph. value close to 4.6. Therefore, you should typically process them in a pressure canner.
Jars of food are placed in 2 to 3 inches of water in a pressure cooker and heated to a temperature of at least 240 degrees F or above for the correct length of time. Note: This temperature can only be reached in a pressure cooker/canner. Never attempt to can low-acid foods using the water bath method.
Steps for Pressure Canning Method
Fill the jars. Allow the proper headspace according to processing directions for specific foods. This is necessary so that all extra air will be removed during processing and a tight vacuum seal will be formed.
To make sure that air bubbles have not been trapped inside the jar, run a bubble freer or any plastic or rubber-like utensil around the edges of the jar, gently shifting the food so that any trapped air is released. After the air bubbles have been removed, more liquid may need to be added to the jar to ensure proper headspace.
Wipe off the rims of the jars with a clean, damp cloth.
Screw on the lids, but not too tightly - air needs to escape during processing
Lift lid inside of metal screw ring with a magnetic lid lifter. The lid lifter can additionally be used to remove lids from boiling water after sterilizing.
Set the jars of food on the rack in the canner so steam can flow around each jar. Add more boiling water or take out some as needed so that the water is at least 1 inch over the tops of the jars. (If you add more water, pour it between the jars, not directly on them to prevent breakage). Put the lid on the cooker.
Keep the pressure constant by regulating the heat under the canner. Keep drafts from blowing on the canner. Fluctuating pressure causes loss of liquid from jars and under-processing.
When the processing is completed, carefully remove the canner from the heat. If the canner is too heavy, simply turn it off.
Let the pressure in the canner drop to zero using the natural release method. Do not use the cold water pressure release method for pressure canning. Do not use the automatic release method to hasten the reduction in pressure when canning foods.
Check to ensure the pressure indicator has lowered. When the canner is depressurized, wait an additional two minutes and then open the lid.
Unfasten the lid, and tilt the far side up, so the steam escapes away from you. Do not leave the canner unopened, or the food inside could begin to spoil. Use a jar lifter to carefully remove the jars from the canner. Place the hot jars on a rack, dry towels, boards or newspaper, right side up to prevent the jars from breaking on contact with a cold surface. Leave at least 1 inch of space between the jars. DO NOT TIGHTEN THE LIDS. Allow the jars to cool, untouched for 12 to 24 hours.
Boiling Water Bath Method:
The boiling water bath method is safe for fruits, and pickles as well as pie filling, jams, jellies, marmalade and other preserves. In this method, jars of food are heated by being completely covered with boiling water (212 degrees F at sea level).
High-acid foods contain enough acid (ph. of 4.6 or less) so that the Clostridium Botulinum (Botulism) spores can't grow and produce heavy toxins. High-acid foods include fruits and properly pickled vegetables. These foods can be safely canned at boiling temperatures in a water bath.
Steps for Boiling Water Bath Method
Fill the pot about halfway with hot water. Turn on the burner and heat the water.
Have the water in the pot hot but not boiling to prevent breakage of the jars when they're placed in the pot.
Follow the same steps detailed in the pressure canner method for filling jars.
When the water in the pot reaches a rolling boil, begin counting the correct processing time. Boil gently and steadily for the recommended time, adjusting the heat and adding more boiling water as necessary.
Use a jar lifter to carefully remove the jars as soon as the processing time is up. Place the hot jars right side up on a rack, dry towels, boards or newspapers to prevent the jars from breaking on contact with a cold surface. Leave at least 1 inch of space between jars. DO NOT TIGHTEN THE LIDS. Allow the jars to cool untouched for 12 to 24 hours.
Recipe is from Fagor's home canning cookbook