Bush: A proper canning primer

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Gardens are growing and farmers markets abound, so now is a great time to learn how to preserve your food at home, says Dr. Janie Burney, a professor and food preservation specialist with the University of Tennessee Extension Department of Family and Consumer Sciences.

During this time of year Burney is often asked by both beginning and experienced food preservationists to review the basics of canning.  Here is how she addressed some recent questions about the use of jars, lids and seals in a home canning operation.

Question:  What kinds of jars should I use for canning?

Burney: The best choices are regular and wide-mouthed Mason-type jars with self-sealing lids. You can purchase these in ½ pint, pint, 1½ pint, quart, and ½ gallon sizes. Some people prefer the wide-mouthed jars because they have larger openings that make them easier to fill and empty.

Question:  Why can’t I use mayonnaise and pickle jars I have collected?

Burney:  You could, but be prepared for problems with broken jars and lids that do not seal well. Jars with the letters “Mason” on them have been designed to withstand the high temperatures needed during water-bath and pressure canning. Mason jars also can be reused many times. Commercial mayonnaise and pickle jars may be weakened by repeated contact with metal spoons or knives. Even the smallest of scratches in glass may cause cracking and breakage in the canner.

Commercial mayonnaise and pickle jars also may have a narrower sealing surface that prevent lids from sealing properly. If they cannot be sealed with a two-piece canning lid, they are not recommended for canning at home.

Question:  What are two-piece canning lids?

Burney:  These are self-sealing lids that consist of a flat metal lid held in place by a metal screw band during processing. These lids are crimped around the bottom edge to form a trough, which is filled with a colored gasket compound. The gasket softens and flows slightly over the jar-sealing surface, which allows air to escape from the jar during processing. The gasket then forms an airtight seal as the jar cools. This prevents air and microorganisms from getting into the jar after it is processed.

Before you apply these lids to your jars, read the manufacturer’s instructions on how to prepare them. They often are simmered in water before they are applied to jars to ensure a good seal.

Question: Can the two-piece lids be reused?

Burney: The flat metal lid cannot be reused and must be replaced each time you process jars. Gaskets from unused lids work well for at least 5 years from the date of manufacture. Older seals may fail to seal on jars, so it is a good practice to buy just enough lids for the current canning season. Also, you should examine the metal lids carefully to be sure there are no gaps or defects in the sealing gasket before using them.

The metal screw bands can be reused provided they are not bent or rusted. These can be removed after processing and jars have sealed, before jars of food are stored.

Question: I have seen some other kinds of lids and jars that look “antique.” Are these okay to use?
Burney: Some specialty stores are selling jars with clip-top lids that have a removable gasket. These are okay if you plan to store your jars of food in the refrigerator. Currently, USDA and Cooperative Extension do not have recommendations for using these types of lids because information on their ability to form a good seal is not available. You will also want to consider the cost. Two-piece canning lids are inexpensive and readily available in discount stores and places where canning supplies are sold. If you use specialty jars, be sure they have mouths that can be sealed with two-piece lids.

Many years ago home canners used zinc lids. These are fine for decorative purposes and for storing buttons, marbles and other items, but they are no longer recommended for canning food.

For more information on safe home canning practices, contact your family and consumer sciences agent at your local county UT Extension office. You also can visit http://nchfp.uga.edu/publications/publications_home.html to print current recipes and USDA’s Complete Guide to Home Canning. More information and recipes may be available on the national extension website:  http://www.extension.org.  Just search the term “canning.”  Burney cautions home canners to use only modern, approved recipes. Heirloom recipes and those found on web sites that end in “.com” may not be safe.

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Carla Bush
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