To safely can any food at home you need to be sure to kill any microorganisms, such as mold or bacteria, during processing.
A water bath canner is perfectly safe to use for processing foods that are high in acid. Foods that are considered high-acid are those with a pH level below 4.6. Acidic foods include fruits, most tomatoes, and pickled foods. The acidic environment inside the jars of high-acid foods is not a favorable environment for bacteria and microorganisms to multiply.
Some potentially harmful microorganisms are not destroyed at the temperature inside a boiling water canner. For instance, the bacteria that can produce botulism toxin is destroyed at 240 degrees F, well above the temperature at which water boils (212 degrees F). Furthermore, the conditions inside a jar of low-acid canned goods is precisely the environment in which botulism toxin can flourish. Botulism is a serious toxin that can cause paralysis or even death.
Considering the potentially dangerous consequences, it is imperative to use a pressure canner to preserve any low-acid food as well as follow a tested and approved recipe. Pumpkin, is an example of a low-acid food that must be canned with a pressure canner. Do not be tempted to experiment with your own recipes or make substitutions to approved recipes. Doing so may alter the pH of the finished food, therefore making it unsafe to can.
Pressure canners are easy to use once you learn the necessary steps to follow. Always follow the instructions accompanying your pressure canner. If you do not have the instructions that came with your canner or have never used a pressure canner before, call your local Agricultural Extension office for an appointment to have your pressure canner tested. Someone should be able to help you inspect the canner's gasket and pressure gauge to ensure they are working properly.
Two kinds of pressure canners are available, weighted gauge canners and dial gauge canners. Weighted gague canners come with a weight that is designed to jiggle or rock a few times a minute when the correct pressure is obtained. Dial gauge canners will display the current pressure inside the canner on an easy-to-read dial. Both types of pressure canners are safe to use, given that you follow the instructions.
Pressure canners must vent steam for 10 minutes after the canner is filled and the lid is locked. This necessary step eliminates the air in the canner, making it possible for temperatures inside the canner to climb high enough for safe processing. After venting, place the weighted gauge on the canner and wait for the gauge to read the appropriate pressure called for in your recipe. Once the correct pressure is obtained you can begin the processing time for your recipe.
Note that instructions in recipes are for canning at or below 1,000 feet in elevation. To safely can foods at higher elevations, you must add additional pressure. Again, follow your canner's instructions or call your local Agricultural Extension office.
Read on for instruction on how to get started canning at home. For additional information on using pressure canners, visit the National Center for Home Food Preservation.