Archive for Wednesday, July 28, 2004

How-to guidelines on pressure canning

July 28, 2004


I purchased a pressure canner without an instruction book at a garage sale. Since I haven't canned for several years, I need instructions on how to pressure can. Will you help me?

For successful pressure canning, follow these steps:

1. Put 2 to 3 inches of hot water in the canner. Place filled jars on the rack, using a jar lifter. Fasten the canner lid securely.

2. Leave the weight off the vent port or open the petcock. Heat at the highest setting until the steam flows from the petcock or vent port.

3. Maintain a high-heat setting, exhaust the steam for 10 minutes, and then place the weight on the vent port or close the petcock. The canner will pressurize during the next 3 to 5 minutes.

4. Start timing the process when the pressure reading on the dial gauge indicates that the recommended pressure has been reached or when the weighted gauge begins to jiggle or rock.

5. Regulate the heat under the canner to maintain a steady pressure at or slightly above the correct gauge pressure. Quick and large pressure variations during processing may cause unnecessary liquid losses from the jars. Weighted gauges on Mirro canners should jiggle about 2 to 3 times per minute. On Presto canners, they should rock slowly throughout the process.

6. When the timed process is completed, turn off the heat, remove the canner from heat if possible, and let the canner depressurize. Do not force the canner to cool. Forced cooling may result in food spoilage. Cooling the canner with cold running water or opening the vent port before the canner fully depressurizes will cause a loss of liquid from the jars and seal failures. Force cooling also may warp the canner lid of older model canners, causing steam leaks.

Depressurization of older model canners should be timed. Standard-sized, heavy-walled canners require about 30 minutes when loaded with pints and 45 minutes with quarts. Newer, thin-walled canners cool more rapidly and are equipped with vent locks. These canners are depressurized when their vent lock piston drops to a normal position.

7. After the canner is depressurized, remove the weight from the vent port or open the petcock. Wait 2 minutes, unfasten the lid, and remove it carefully. Lift the lid away from you so that the steam does not burn your face.

8. Remove the jars with a lifter and place on a cooling rack. When you remove hot jars from the canner, do not retighten their jar lids. Retightening the hot lids may cut through the gasket and cause seal failures. Cool the jars at room temperature from 12 to 24 hours.

How do I check to make sure the lids are sealed?

After cooling the jars from 12 to 24 hours, you can remove the screw bands and test the seals using one of the following options:

  • Option 1: Press the middle of the lid with a finger or thumb. If the lid springs up when you release your finger, the lid is unsealed.
  • Option 2: Tap the lid with the bottom of a teaspoon. If it makes a dull sound, the lid is not sealed. If the food is in contact with the underside of the lid, it also will cause a dull sound. If the jar lid is sealed correctly, it will make a ringing, high-pitched sound.
  • Option 3: Hold the jar at eye level and look across the lid. The lid should be concave. If the center of the lid is either flat or bulging, it may not be sealed.

Can food be recanned if the lid does not seal?

Canned food safely can be recanned if the unsealed jar is discovered within the first 24 hours. To recan, remove the lid and check the jar-sealing surface for tiny nicks. If necessary, change the jar, add a new properly prepared lid, and reprocess using the same processing time. Head space in unsealed jars may be adjusted to 1 1/2 inches, and the jars could be frozen instead of reprocessed.

Foods in single, unsealed jars could be stored in the refrigerator and consumed within several days.

How can I remove hard-water deposits or film from my canning jars?

To remove hard-water deposits, soak the jars for several hours in a solution of 1 cup of vinegar and 1 gallon of water.

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