Pressure Canner Use

Pressure canners are safe and economical to use when operated according to safety rules.  Pressure canning is a method of preserving low acid foods which has been used for decades—especially by home gardeners and others interested in providing food storage for their families using the quality produced produced by the gardeners own hands.  Pressure canners for home use were extensively redesigned beginning in the 1970's. Before the 1970's, pressure canners were typically heavy-walled kettles with clamp-on or turn-on lids fitted with a dial gauge, a vent port in the form of a petcock or covered with a counterweight, and a safety fuse.  Modern pressure canners are generally lightweight, thin-walled kettles usually with turn-on lids fitted with a gasket that must be periodically replaced.  All canners have removable racks, an automatic vent/cover lock, a vent port (steam vent), and a safety fuse.  The modern pressure canner may have a dial gauge for indicating the pressure or a weighted gauge, for indicating and regulating the pressure.  Pressure canners generally are deep enough for one layer of quart or smaller size jars, or deep enough for two layers of pint or smaller size jars.  The All American brand pressure canners made by the Wisconsin Aluminum Factory Company are relatively heavy canners with screw-down knobs around the canner, both a gauge and a weight, and no gasket to wear out.  This line of canners comes in a variety of sizes from small to very large.  

Why Use a Pressure Canner to Preserve Food?

Home food preservation promotes a sense of personal satisfaction and accomplishment.  Further, the guess-work is taken out of being able to provide a safe food supply at home when guidelines for operating a pressure canner are followed exactly, scientifically tested/approved recipes are utilized, and high quality equipment, supplies and produce are used.  Low acid foods require a higher temperature when processing than can be achieved using the boiling water canning methods.  To kill harmful bacteria (such as those associated with botulism) use of pressure canning ensures the safety of the preserved produce.  Foods such as red meats, sea food, poultry, dairy products, and all fresh vegetables, with the exception of most tomatoes, fit into the low acid group since they have an acidity, or pH level, of 4.6 or higher.  The temperature which must be reached and maintained (for a specified amount of time) to kill the harmful bacteria that can be present in low acid foods is 240 to 250 degrees Fahrenheit.  Since water boils at 212 F (and does not get hotter), boiling water cannot reach this temperature.  This temperature can be reached only by creating steam under pressure (note: steam canners also do not reach higher temperatures and should only be used with water-bath canning recipes).  Pressure canners operated at 10 to 15 pounds pressure can attain the required temperatures and produce safe, home-canned, low-acid products. 

If you plan to use a pressure canner, determine if it's equipped with either a dial gauge or a weighted gauge.  Dial gauges should be checked for accuracy.  They can be checked at some University Extension Service offices.  Or check with the canner manufacturer to see if they will check your gauge.  Weighted gauges are always accurate and do not need to be checked.

Pressure Canner Errors

Serious errors in pressure canner food processing can occur if any of the following conditions exist:

  • The canner is operated at an altitude above sea level.  Internal canner pressures (and therefore temperatures) are lower at higher altitudes.  Therefore, unless you are located at or near sea level, you must increase pressures according to recipe or canner instructions in order to compensate for this altitude effect.  

  • Air is trapped in the closed canner during the process.  Air trapped in a pressure canner lowers the temperature obtained for a given pressure and results in under processing.  To be safe, all pressure canners must be vented for 10 minutes before they are pressurized.

    To vent your pressure canner, leave the vent port (steam vent) uncovered (or manually open the petcock on some older models) after you fill the canner and lock the canner lid in place.  Heat the canner on high until the water boils and generates steam that can be seen escaping through the open vent port or petcock.  When a visible funnel-shape of steam is continuously escaping the canner, set a timer for 10 minutes.  After 10 minutes of continuous steam, close the petcock or place the counterweight or weighted gauge over the vent port to begin pressurizing the canner. (See steps 3 and 4 below.)

  • An inaccurate dial gauge is used.  Dial gauges should be checked for accuracy each year before use.  If the gauge reads high or low by more than one pound at 5, 10 or 15 pounds pressure, replace it.  Weighted gauges are always accurate.  If your canner has both gauge and weight, also go by the weight using the gauge as a guide only.

Always operate your pressure canner according to the manufacturer’s directions.  Only use canners that have an Underwriter’s Laboratory (UL) approval.

Follow these steps for successful pressure canning:
(Read through all the instructions before beginning.)

  1. Center the canner over the burner. When you have your jars of food ready for canning, put the rack and 2 to 3 inches of hot water into 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.

  2. Place filled jars, fitted with lids and rings, 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 screw 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 port or open the petcock.

  4. Turn up the heat to its highest position.  Heat until the water boils and steam flows freely in a funnel-shape from the open vent port or petcock. While maintaining the high heat setting, let the steam flow (exhaust) continuously for 10 minutes.

  5. After this venting of the canner, place the counterweight or weighted gauge on the ventport, or close the petcock.  The canner will pressurize during the next 3 to 5 minutes.

  6. Start timing the process when the pressure reading on the dial gauge indicates that the recommended pressure has been reached.  For canners without dial gauges, start timing when the weighted gauge begins to jiggle or rock.

  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 2 or 3 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.

    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 and let the canner cool down naturally.  While it 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 port before the canner is fully depressurized are types of forced cooling. They will also cause loss of liquid from jars and seal failures.  Force cooling may also warp the canner lid.

    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 depressurized, remove the weight from the vent port or open the petcock.  Wait 2 minutes (as a safety precaution), 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.  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.