Choosing and using Canning jars wisely

Home Canning Jars

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Home Canning aka small batch preserving food is an awesome way to save and savor summers bounty from your own little garden and save and savor some money as well. The canning jars that you choose and use are a key element of this endeavor.

Mason Jars commonly used in home canning or preserving

99.9 % of all canning, give or take a decimal point or two requires the heating and cooling of food, largely to form a vacuum seal. Food packed into mason or canning jars has 'headspace' which is filled with air. During temperature processing, air is forced out of the jars and replaced with steam. Once the jars cool off and the steam returns to liquid form the contents of the canning jar will shrink which helps form a vacuum seal. The pressure from this vacuum seal holds down the lid. When sealing compound, such as beeswax is used on the lid, it prevents air from leeching back into the jar.

Along with the air comes microorganisms that have the potential of contaminating the food. Glass Jars specifically designed for freezing and canning should be used, mason jars are the most popular but others such as anchor hocking and so forth will suffice.

Canning jars should be inspected before being used, any imperfections should be discarded. Nicks, chips, cracks - even hairline cracks exclude jars from use.

When using a boiling water bath use a rack at the bottom of the canner to keep the jars from coming into contact with metal on the bottom of canner. Avoid using metal utensils when removing air bubbles from hot jars, a rubber spatula or similar utensil works best.

Recommendations on headspace found in many recipes may seem trivial but they are not. Headspace Allows the food to expand in jars when heated and to form a proper seal.


After processing, wait Until the Jars Have Cooled before tightening the bands. Adjusting the bands, while the jar is hot will disturb the gasket, and cause failed seals. It's okay if the bands have loosened a bit while processing. Allow the jars to cool off at room temperature for 12 to 24 hours before testing the seals. You may notice that the level of the contents is lower than when you first packed the jars. This is normal. Do not open the jars and add more food. Once you break the seal, and add more food you'll have to reprocess the whole shebang.

The National Center for Home Food Preservation advises canning jars should be used for no more than 10 years, so long as they are handled properly.

Supplies Home Canning