For home gardeners it’s tempting to fill every available space on shelves and in a freezer with a season’s bounty, but food preservations experts warn there can be a real danger when one’s canning exceeds their annual food needs.
“Honey found in thousand-year-old Egyptian tombs is still good,” Laurie Bowen with University of Maine Cooperative Extension said. “But that’s not the case with home canning.”
Unless a home food preserver has friends or family to whom they can pass along the surplus, Bowen recommends being realistic and preserve only what is needed for the year. How much is that? It depends on individual appetites and family needs.
“There is a shelf life in home canning,” Bowen said. “If properly processed and preserved, food is good for a year. That is why we caution that it is easy to get carried away and find you have more canned than you can eat in a year.”
The biggest worry with edibles like string beans, carrots or peas is botulism.
According to The World Health Organization and FoodSafety.gov, foodborne botulism is a rare but serious illness that produces a toxin affecting the nerves. The most common sources of the disease are home-canned foods with low acid content, improperly canned commercial foods or foods kept in warm conditions for extended periods of time.
The incubation period is 12 to 72 hours, and symptoms include double vision, blurred vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth and muscle weakness. If Botulism is suspected, the individual should seek emergency medical care immediately.
According to the United States Centers for Disease Control and Prevention, there were no cases of foodborne botulism in Maine in 2017, the most recent year for which data is available.
By using tried and true techniques of boiling water or pressure canning, proper storage and keeping track of shelf life, Bowen said home-canned foods are perfectly safe.
“Most things that are canned should be stored in cool, dark places between 50 and 70 degrees,” she said. “It is also very important to label everything with what the jar contains and the date it was canned.”
Canned items such as pickles or tomatoes that are high in acidity can last a bit longer than 12-months, but Bowen said the one-year limit is a good rule of thumb, regardless.
“We recommend using tested recipes that have been proven over time,” she said. “Make sure you are using fruits and vegetables at their peak and that are not mushy or have gone by.”
Before beginning the process, Bowen said home-canners should inspect their jars thoroughly for any chips that could hinder possible sealing and don’t re-use any old lids.
All vegetables should be carefully and thoroughly trimmed, peeled and washed before they are canned to lower the microbial load.
Underprocessing can leave active microbes in the cans that will develop into toxins over time. To prevent this, according to the Extension, make sure to use proper, working equipment with the correct processing times.
For less acidic vegetables such as beans, carrots, peas, turnips or meats and soups, Bowen said a pressure canner is required. In order to prevent spoilage for those low-acid foods, they must be processed at 240 degrees Fahrenheit for the indicated time. The only way to get to that temperature is with a pressure canner as a simple water bath maxes out at 212 degrees — the temperature of boiling water.
Because the botulism spores do not grow in the presence of acid, those foods — anything using vinegar, for example — can be safely processed in a boiling-water canner.
After the jars come out of their hot water bath or pressure canners, within 12 hours they should make that satisfying “pop” sound indicating vacuum action within the jars has “sucked” in the lids and sealed them completely.
She also said it’s a good idea to remove the screw-rings from the jars after the seal is formed. Over time, she said those rings can exert pressure and break the seal.
From that point on, Bowen said, just keep an eye on them.
“Obviously, if you see mold or yeast, discard the jar and its contents immediately,” she said. “And if you open the jar and the food squirts out? That is not good.”
Other things to look for as signs of spoilage are bulging tops on the jars, lack of a seal, scum on top of the food, the food looks “bubbly,” unnatural colors and unnatural smells.
“When in doubt, toss it out,” Bowen said. “Never, ever give it the taste test.”
But, be careful then too, Bowen said. Animals can get into spoiled foods and get just as sick as humans.
“I like that people are going back to home canning and food preservation,” Bowen said. “When people think of artisan foods, they usually just think of bread, but food preservation is also an art.”