Homemakers use Mason jars in home kitchens to can or preserve food for storage. The glass jars are designed to withstand the high temperatures safe canning requires. They are sealed airtight during the canning and cooling process, when the rubber edge of a metal jar lid softens and spreads slightly over the jar edge. A metal ring or band loosely secures the lid during canning, and permits air from the jar to escape. As the jars cool after canning, a vacuum forms and pulls the lid down into a seal. Homemakers often listen for a reassuring popping sound after canning, alerting them to the successful seal.
Things You'll Need
- Mason jars
- Canning lids
- Canning screw bands or rings
- Damp, clean cloth
- Dry cloth
Scoop or spoon food into a sterilized, hot Mason jar. Allow 1/2 inch head space between the contents and the jar top.
Run a rubber spatula around the inside of the jar to force air bubbles out of the food and jar. Wipe the top and sides of the jar rim carefully with a damp, clean cloth or paper towel. This will remove any food residue that could prevent a good seal.
Cap the Mason jar with a clean, new lid. Move the lid into place so the rubber edge fits snugly on the jar rim.
Secure the lid with a clean metal canning ring. Screw the ring on loosely to allow steam and air to escape during canning.
Remove the Mason jars after processing the food in a canner. Don't tighten the rings. Set the hot jars on a dry cloth on a table or counter to cool.
Wait for a popping sound from each jar before removing the metal rings or bands. Run your finger across the lid after the Mason jars cool completely. A sealed jar will present a concave lid center, indicating a successful vacuum.
- University of Georgia National Center for Home Food Preservation: General Canning Information
- “Ball Blue Book”; Ball Corporation; 1999
- Photo Credit Jupiterimages/Brand X Pictures/Getty Images
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