Pressure Canner

A pressure canner is a specially-made heavy pot with a lid that can be closed to prevent steam from escaping. The lid is fitted with a vent (or petcock), a dial- or weighted-pressure gauge, and a safety fuse. Newer models have an extra cover lock as an added precaution. It may or may not have a gasket. The pressure canner also has a rack. Because each type of a canner is different, be sure to read the directions for operating your canner and keep them for future reference.

Invisible microorganisms are present all around us. Fruits, vegetables, meat, poultry and seafood contain these microorganisms naturally. Yet, they are not a problem unless food is left to sit for extended periods of time, causing food spoilage. This is nature’s way of telling us when food is no longer fit to eat.

There are four basic agents of food spoilage – enzymes, mold, yeast, and bacteria. Canning will interrupt the natural spoilage cycle, so food can be preserved safely. Molds, yeast, and enzymes are destroyed at temperatures below 212° F, the temperature at which water boils (except in mountainous regions). Therefore, boiling water processing is sufficient to destroy those agents.

Bacteria, however, are not as easily destroyed. The bacteria, Clostridium botulinum produces a spore that makes a poisonous toxin which causes botulism. This spore is not destroyed at 212° F. In addition, bacteria thrive on low acids in the absence of air. Therefore, for a safe food product, low-acid foods need to be processed at 240° F. This temperature can only be achieved with a pressure canner.

Follow these steps for successful pressure canning:

  1. Make sure the pressure canner is working properly before preparing food. Clean lid gaskets and other parts according to the manufacturer’s directions; make sure all vent pipes are clear and contain no trapped material or mineral deposits. Center the canner over the burner. The burner and range must be level. Your pressure canner can be damaged if the burner puts out too much heat. In general, do not use on an outdoor LP gas burner or gas range burner over 12,000 BTU’s. Check your manufacturer’s directions for more information about appropriate burners.

    Put the rack and hot water into the canner. If the amount of water is not specified with a given food, use enough water so it is 2 to 3 inches high in the canner. Longer processes required more water. Some specific products (for example, smoked fish) require that you start with even more water in the canner. Always follow the directions with USDA processes for specific foods if they require more water be added to the canner.

    For hot packed foods, you can bring the water to 180 degrees F. ahead of time, but be careful not to boil the water or heat it long enough for the depth to decrease. For raw packed foods, the water should only be brought to 140 degrees F.

  2. Place filled jars, fitted with lids and ring bands, on the jar rack in the canner, using a jar lifter. When moving jars with a jar lifter, make sure the jar lifter is securely positioned below the neck of the jar (below the ring band of the lid). Keep the jar upright at all times. Tilting the jar could cause food to spill into the sealing area of the lid.
  3. Fasten the canner lid securely. Leave the weight off the vent pipe or open the petcock.
  4. Turn the heat setting to its highest position. Heat until the water boils and steam flows freely in a funnel-shape from the open vent pipe or petcock. While maintaining the high heat setting, let the steam flow (exhaust) continuously for 10 minutes.
  5. After this venting, or exhausting, of the canner, place the counterweight or weighted gauge on the vent pipe, or close the petcock. The canner will pressurize during the next 3 to 10 minutes.
  6. Start timing the process when the pressure reading on the dial gauge indicates that the recommended pressure has been reached, or, for canners without dial gauges, when the weighted gauge begins to jiggle or rock as the manufacturer describes.
  7. Regulate the heat under the canner to maintain a steady pressure at, or slightly above, the correct gauge pressure. One type of weighted gauge should jiggle a certain number of times per minute, while another type should rock slowly throughout the process – check the manufacturer’s directions.
    • Loss of pressure at any time can result in under processing, or unsafe food.
    • Quick and large pressure variations during processing may cause unnecessary liquid losses from jars.

    IMPORTANT: If at any time pressure goes below the recommended amount, bring the canner back to pressure and begin the timing of the process over, from the beginning (using the total original process time). This is important for the safety of the food.

  8. When the timed process is completed, turn off the heat, remove the canner from the heat (electric burner) if possible, and let the canner cool down naturally. (Lift the canner to move it; do not slide the canner. It is also okay to leave the canner in place after you have turned off the burner. It is better to do so than to let jars inside the canner tilt or tip over if the canner is too heavy to move easily.)

    While the canner is cooling, it is also de-pressurizing. Do not force cool the canner. Forced cooling may result in food spoilage. Cooling the canner with cold running water or opening the vent pipe before the canner is fully depressurized are types of forced cooling. They will also cause loss of liquid from jars and seal failures. Forced cooling may also warp the canner lid.

    Even after a dial gauge canner has cooled until the dial reads zero pounds pressure, be cautious in removing the weight from the vent pipe. Tilt the weight slightly to make sure no steam escapes before pulling it all the way off. Newer canners will also have a cover lock in the lid or handle that must release after cooling before the lids are twisted off. Do not force the lid open if the cover locks are not released. Manufacturers will provide more detailed instructions for particular models.

    Depressurization of older canner models without dial gauges should be timed. Standard size heavy-walled canners require about 30 minutes when loaded with pints and 45 minutes when loaded with quarts. Newer thin-walled canners cool more rapidly and are equipped with vent locks that are designed to open when the pressure is gone. These canners are depressurized when the piston in the vent lock drops to a normal position. Some of these locks are hidden in handles and cannot be seen; however, the lid will not turn open until the lock is released.

  9. After the canner is completely depressurized, remove the weight from the vent pipe or open the petcock. Wait 10 minutes; then unfasten the lid and remove it carefully. Lift the lid with the underside away from you so that the steam coming out of the canner does not burn your face.
  10. Using a jar lifter, remove the jars one at a time, being careful not to tilt the jars. Carefully place them directly onto a towel or cake cooling rack, leaving at least one inch of space between the jars during cooling. Avoid placing the jars on a cold surface or in a cold draft.
  11. Let the jars sit undisturbed while they cool, from 12 to 24 hours. Do not tighten ring bands on the lids or push down on the center of the flat metal lid until the jar is completely cooled.
  12. Remove ring bands from sealed jars. Ring bands can be washed and dried and put away for using another time. Put any unsealed jars in the refrigerator and use first.
  13. Wash jars and lids to remove all residues.
  14. Label jars and store in a cool, dry place out of direct light.
  15. Dry the canner, lid and gasket. Take off removable petcocks and safety valves; wash and dry thoroughly. Follow maintenance and storage instructions that come from your canner manufacturer.

Vent or Petcock: This is a short, hollow pipe that sticks up above the canner lid. When open, it allows air and steam to escape from the canner. When closed, it holds the steam inside. On newer canners the vent is closed or opened using a separate pressure regulator weight. On older canners, the vent may be closed using a valve or screw that you can turn.

Pressure Gauge: This registers the pressure inside the canner. A dial gauge will actually show the temperature and/or pressure inside the canner. The weighted gauge will rock gently or make a “jiggling” noise periodically to show that correct pressure is being maintained. Read the manufacturer’s instructions to see how often the weight should rock or jiggle. Some canners have a three-piece weighted gauge that can regulate 5, 10 or 15 pounds of pressure. For 10 pounds of pressure, one piece of the weight is left off.

Recent tests have shown that dial gauges and weighted gauges actually register slightly different pressures. Because of this, dial gauges are operated at 11 pounds pressure up to an altitude of 2,000 feet. At altitudes over 2,000 feet, corrections must be made for dial-gauge canners. Weighted-gauge canners can be operated at 10 pounds pressure up to an altitude of 1,000 feet. At altitudes over 1,000 feet, correction must be made for weighted-gauge canners.

Gasket: This is a rubber or rubber-like compound that helps seal the edges of the canner and lid to prevent steam from escaping. Gaskets may be removable for cleaning or replacement. (Not all pressure canners have gaskets. Some have a metal-to-metal seal.)

Safety Checks for Pressure Canners: For safe operation, the vent, safety valve and edges of the lid and canner must be clean at all times. To clean the vent, draw a string or narrow strip of cloth through the opening. The dial gauge on a canner should be checked for accuracy yearly. Check with your county Extension agent well in advance of each canning season for instructions on how this can be done. If the gauge is off more than 1 pound at 5, 10 or 15 pounds of pressure, it should be replaced. Follow the manufacturer’s directions for care of the sealing edges of your canner.

Pressure Saucepans & Other Unsafe Models: Small pressure saucepans are not recommended for home canning. Also, outmoded and potentially unsafe pressure canners should not be used. Compare old canners with newer models to be sure that what you have is actually a pressure canner and not an old sterilizer or steamer. Before using an old canner, make sure all parts have been checked and are working properly. Buying an old second-hand canner may not be a bargain. Sometimes replacement parts are no longer being made.

Storing Canned Food
Once jars of food have been canned and thoroughly cooled, it is important to test the seals before storing. Press down on the center of the lid. If it is concave, or stays down when pressed, the jar is properly vacuum sealed. After 12 to 24 hours, remove bands and wipe off any food residue from bands and jars. If bands are left on, they may rust and become difficult to remove. Store canned food in a cool, dark, and dry place. Home canned food can be kept for many years. However, after one year the quality will begin to deteriorate. For this reason, always date and label jars before storing. Though your memory may serve you well, squash and pumpkin will look remarkably similar when making Thanksgiving pie.

NOTE: Always follow the recommended times and pressure levels in your pressure canning recipes.

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