Can You Pressure-cook Canned Foods?

Pressure canning is one of the predominant methods used to can foods. Pressure-cooking the food in canning jars is the safest method for preserving low-acid foods, such as meats and vegetables. Pressure canning is even safer than the other predominant canning method -- the boiling water bath. Most pressure canning is done using a special pressure canner, although some pressure cooker manufacturers provide instructions for using their machines effectively for canning purposes.

Principles

A pressure cooker is one of the only food-heating implements outside of an oven that can reach the minimum temperature of 240 degrees Fahrenheit necessary to eradicate the harmful Clostridium botulinum bacteria. This bacteria can grow in food, in particular foods with low acidity stored in the absence of air. Boiling water can kill the microorganisms themselves but may leave behind spores that can withstand those temperatures and grow to produce the toxins that can cause fatal botulism.

Equipment

While you can pressure can in a pressure cooker, it is far easier to use a pressure canner designed for the job. Pressure canners are typically deeper than pressure cookers and capable of holding at least four quart-sized jars and typically more like 16 quart-sized jars. Pressure canners contain more metal and use more water than pressure cookers, which makes the heating and cooling times shorter.

Process

Fill clean canning jars with the food to be preserved and seal the lids tightly. Place the filled, sealed canning jars in a pressure canner in 2 to 3 inches of water. After heating up the pressure canner and before closing its valve or weighting its vent, exhaust the canner for 10 minutes to let steam escape. This ensures that the pressure gauge gives an accurate reading of the temperature inside the canner. How long to leave food in a pressure canner is a matter of how long it takes for the filled canner to come up to the proper temperature, then come back down to the temperature and pressure at which you can remove the processed jars.

Foods

Only fruits and pickled vegetables have enough acid in them to safely can using the boiling water method. All meats, including poultry and seafood; vegetables; and dairy products lack sufficient acid to naturally prevent the deadly bacteria from growing and must be pressure-canned to store safely for any length of time without spoilage

Considerations

After pressure-canned jars have cooled for at least 24 hours, their seals should be completely secured. This mean the lids are pulled tightly against the lip of the jars and the center of the lids are pulled in toward the interior of the jar. When you press on the center of the lid, there should be no give whatsoever. Otherwise, you don't have a complete seal and botulism is still possible.