Preserving Food: Using Pressure Canners

Elizabeth L. Andress, Ph.D.
Associate Professor and Extension Food Safety Specialist,
Department of Food and Nutrition
Document Use:

Serious errors in processes obtained in pressure canners can occur if any of the following conditions exist:

• The altitude at which the canner is operated is above sea level. Internal canner pressures (and therefore temperatures) are lower at higher altitudes. Canners must be operated at increased pressures as the altitude increases. Check canning instructions for altitude adjustments.

   

• Air is trapped in the closed canner during the process. Air trapped in a pressure canner lowers the temperature obtained for a given pressure (for example, 10 or 15 pounds pressure) and results in underprocessing. To be safe, all pressure canners must be vented 10 minutes before they are pressurized.

  To vent a 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, you can 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. If the gauge reads low by 1 pound or less, add that amount to the recommended pressure. (For example, if your gauge reads 9.5 pounds when it should read 10 pounds, add 1/2 pound to the recommended pressure, or use 10.5 instead of 10 pounds.)

Clean lid gaskets and other parts according to the manufacturer’s directions. Use only canners that have the Underwriter’s Laboratory (UL) approval to ensure their safety.

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, 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 the heat setting 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, or exhausting, 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, 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 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 underprocessing, 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, remove the canner from the heat (electric burner) if possible, 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.