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July 7, 2010 Volume 31, No. 33

Yes, you can

Garden bounty

Home canning helps people reconnect with food

You can can nearly everything. From fruits and vegetables, to soups and broths, to meat, fish and poultry, canning is a way to preserve most foods, says Vera Massey, University of Missouri Extension nutrition and health education specialist.

Massey started canning with her mother and grandmother when she was a young child. “I would check the canning jars for cracks,” she says. Today Massey passes on the knowledge and techniques of home food preservation once common in American homes, and after 36 years at MU Extension, Massey says canning is seeing a surge in popularity.

“There is a lot to know about food preservation,” Massey says. “Freezing and drying are the simplest, but canning has its advantages.” Canning doesn’t require power after the process is complete, unlike freezing, and many people enjoy the unique taste and texture of canned foods. The canning process preserves food by removing oxygen, destroying enzymes that cause deterioration, preventing growth of bacteria, yeast and molds, and forming a vacuum seal.

There are only two safe ways of canning, depending on the type of food being canned. A pressure canner is used for low-acid foods (vegetables, meats, poultry and fish) and a boiling-water bath canner for high-acid foods (fruits, jams and pickles).

Botulism, a deadly type of food poisoning, is a serious concern for the home canner. Clostridium botulinum bacteria are the main reason why low-acid foods must be pressure canned to be safe. Clostridium botulinum is found in soil and if not destroyed during the canning process, can produce a deadly toxin. The two primary conditions that favor its growth are low acidity and absence of air (such as a sealed canning jar).  Properly operated, a pressure canner reaches 240 degrees Fahrenheit, destroying the Clostridium botulinum spores. But if the food isn’t properly processed, a breeding ground for botulism is created. One milligram of botulism toxin can kill 655 tons of mice. Massey isn’t sure what 655 tons of dead mice look like, and she doesn’t want to find out.

High-acid foods are canned with a boiling-water bath canner because they contain enough acid (pH of 4.6 or less) so the Clostridium botulinum spores will not germinate and produce the deadly toxin. A simple stockpot with a lid will work as a boiling-water bath canner, as long as it’s deep enough to allow for at least 1 inch of briskly boiling water to cover the jars. Massey says to only use tested recipes with a known pH. Because tomatoes have pH values that fall close to 4.6, you need to take precautions to can them safely. Be sure to add acid to your home canned tomatoes (either citric acid or lemon juice), whether they will be processed in a boiling water bath or pressure canner.  “Canning isn’t cooking; follow the recipe,” Massey says.

Massey recommends a trial run without food the first time you use a pressure canner. “It’s going to make sounds, learn what they are and get used to them,” she says. The trial run will also let you find the appropriate burner settings on your stove. It should be noted that most flattop stoves are not designed for use with a pressure canner. Also, be sure to test the accuracy of the dial gauge on your pressure canner before use each year. This can be done at the Boone County Extension Center. While processing, a constant pressure and temperature are necessary. If at anytime your pressure drops below the necessary level, you must start the processing time over. “I always err on the side of over processing,” Massey says.

She prefers a wide-mouth jar because they are easier to fill and get products out of. Initial costs to start canning are $80 for a pressure canner and $25 for a boiling-water bath canner. Jars range in price, but Massey says that if they are taken care of, jars can last for years. Be sure to use two-piece lids for sealing the jars to allow the air to escape from the jar during the caning process. The flat metal disc with the sealing compound around the outer edge is used only once, but the screw band can be used over and over again, unless it rusts or is bent. Other necessary canning equipment is a rack to keep the jars from touching the bottom of the pan, a funnel to fill the jars and a jar lifter to remove the jars from the canner.

Massey teaches multiple classes on freezing, drying and canning techniques every year. She can be reached at the Boone County Extension Center and welcomes questions. If you plan on taking a class, register quickly; Massey says the last three years classes have been full.

The National Center for Home Food Preservation, located at the University of Georgia, is the leader in home food preservation research. She recommends visiting their website — — to see all it has to offer.  

Massey feels the rise in the popularity of canning is related to the sustainable, local food movement. “It’s reconnecting with food and gardening,” she says. “Canning is something families can do together. It’s a lot of work, but it’s also fun.” 

— Josh Chittum