How to Heat Process Mason Jars to Seal

by Leda Meredith

There are two primary ways to process Mason jars to seal them: in a boiling water bath or in a pressure canner. The method you use depends on the kind of food you are canning. Acidic foods such as pickles and fruits may be processed in a boiling water bath, but more alkaline foods such as soup stocks and plain vegetables can only be safely processed in a pressure canner.

Processing Mason Jars

Look up the food you intend to process with a reputable resource such as the National Center for Home Food Preservation. Note both the canning method and the processing time.

Process acidic foods in a boiling water bath. Place a rack inside a large pot and the jars of food, lids closed, on the rack. Add water to completely cover the jars by 1 to 2 inches. Bring the water to a boil and process for the recommended time.

Process alkaline foods in a pressure canner. Load the jars into the canner with the amount of water recommended by the manufacturer. Leave the vent, or petcock open and turn the heat on high. Allow steam to vent for 7 to 10 minutes before closing the vent. Once the pressure is at the recommended level, begin timing the processing.

Remove the Mason jars from either the boiling water bath or the pressure canner with jar-lifting tongs. Do not move the jars again until they have cooled completely. The lids will seal as the jars cool.

Items you will need

  • Mason jars
  • Canning lids
  • Large stock pot or pressure canner
  • Rack
  • Jar lifter


  • Old-fashioned methods of sealing Mason jars in an oven or by turning the jars of hot food upside down are not approved as safe by the U.S. Department of Agriculture.

About the Author

Leda Meredith is the author of two books, including "The Locavore's Handbook: The Busy Person's Guide to Eating Local on a Budget." Specializing in wild edible plants, she is also an instructor at the New York Botanical Garden and the Brooklyn Botanic Garden.

Photo Credits

  • Images