Improving the Safety and Quality of Canned Goods

Use the Proper Canning Method for the Food being Canned

Pressure Canning

• Low acid foods must be processed in a pressure canner.
• Low acid foods include plain vegetables, meats, seafood, poultry, and foods that are combinations of meats, tomatoes and/or vegetables.
• The temperature in a pressure canner is higher than the boiling point of water.
• Temperature in a vented canner is 240°F at 10 pounds pressure in a weighted gauge canner or 11 pounds pressure in a dial gauge canner at altitudes up to 1,000 feet.

Water Bath and Atmospheric Steam Canning

• High acid foods may be processed in a boiling water canner or atmospheric steam canner.
• High acid foods include most fruits, acidified products such as pickles, relishes, and acidified tomatoes.
• Sweet spreads such as jams, jellies, marmalades and conserves must be processed in a water bath or atmospheric steam.
• The temperature of boiling water or atmospheric steam at sea level is 212°F.
• At altitudes above 1,000 feet make an adjustment in processing time.

Tips for Success

• Fill jars with hot food when appropriate (hot pack). If the product is packed into the jar raw (unheated, raw pack), the air inside the food will be forced out during processing and rise to the top of the jar. Processing causes this air to expand and syrup or liquid to seep out of the jar as the lid is venting.
• Keep food hot while filling the jars. Allowing "hot pack" food to cool before processing causes under-processing. The heat curves are based on the food being hot at the beginning of the process. Canned meat, soup, vegetables, or salsa that are under processed can cause botulism.
• Avoid packing product too tightly in jars; allow space for liquid to surround the food. Jars of soup should be filled with one-half solids and the remainder of the space is liquid. Pickles and relishes need adequate brine to provide sufficient acidity.
• Remember to acidify tomatoes, Asian pears, and figs.
• Maintain an even temperature while processing. Extreme temperature variation causes expansion of the contents in the jar forcing liquid out.
• Allow the temperature inside the jars to stabilize with the outside temperature before removing jars from the canner.
• After processing in a water bath canner, remove the lid and allow jars to sit in the hot water for 5 minutes before removing them to a cloth-covered surface to cool.
• Do not force cool a pressure canner. Allow it to cool naturally to 0 pounds pressure. Wait 2 minutes and remove weighted gauge or pressure regulator. Wait 10 more minutes before removing the lid--this will reduce siphoning (loss of liquid from the jar).

Headspace

• Use proper headspace
• Headspace varies by type of food. Refer to recipe for the amount.
• Headspace will increase as the food cools in the jar.
• Correct headspace reduces siphoning.
• If there is too little headspace, the contents may boil out during processing.
• If there is too much headspace, a weak seal may occur.
• Extra headspace leaves more air in the jar and can cause food to discolor due to oxidation.

Process to get a Strong Vacuum Seal

• Follow a research-tested recipe to determine the correct processing method and time.
• Start counting process time when water comes to a steady boil in a water bath canner.
• Allow a column of steam at least 6 to 10 inches long to form from the vent of an atmospheric steam canner before starting the process time.
• Process time in a pressure canner begins after the canner has been vented ten minutes, the pressure regulator has been applied, and the dial reaches the correct pressure or the weight jiggles the correct number of times per minute according to the model of the canner.

Is the Jar Sealed?

• Test for a strong seal after the jars have totally cooled (12- 24 hours). Remove the screw band and lift the jar by picking it up by the lid; it should be strong enough to hold its seal. Look at the lid and the center should curve down. Gently press the center of the lid--it should not flex up and down.
• If a jar is not sealed, do one of the following within 24 hours - remove the lid, check jar rim and re-jar if necessary, apply a new lid and process as before or refrigerate and use within 3 days or freeze.
• Jars that become unsealed during storage should be discarded.

Additional information about canning safe and quality products is found in Penn State Extension's Let's Preserve Basics of Home Canning.

References

LaBorde, L.; Zepp, M.; & Hirneisen, A. (2023, August 1). "Let's Preserve: Tomatoes". Penn State University.

LaBorde, L.; Zepp, M.; & Hirneisen, A. (2023, March 1). "Let's Preserve: Basics of Home Canning". Penn State University.

Zepp, M. (2024, February 12). "Why Allow Headspace when Canning and Freezing Food." Penn State University.