University Extension canning experts have been bombarded with questions this summer as bountiful gardens have piqued interest in preserving the produce by canning it.
The questions, mostly from a new generation of would-be canners, vary. Is it safe to tweak tested recipes? Can canners create new recipes? Is it OK to substitute paraffin for canning lids?
The answer to all three questions is an emphatic “no,” said Julie Garden-Robinson, North Dakota State University Extension food and nutrition specialist, and Suzanne Driessen, a St. Cloud-based University of Minnesota Food Science Extension educator who specializes in canning.
While younger gardeners turn to social media to learn about canning, those sites may contain inaccurate information, Garden-Robinson said. Years of research and testing by Extension experts has determined the safest way to can, and changing the methods could compromise that.
“You really need to make sure it’s a tested recipe,” Driessen said. “You can’t throw a little bit of this and that in there because it’s based on specific amounts and ingredients. It’s based on science.”
For example, canning pickles the correct way calls for using vinegar that has an acidity level of 5% or greater, she said. Though some stores show bottles of vinegar with acidity levels lower than that in their canning displays, those should not be used for preservation.
“You use 5% to make sure sure you have enough acidity in that product,” Driessen said.
Meanwhile, some Extension-tested recipes – such as salsa, which contains tomatoes – must have citric acid or lemon juice added to make them safe, Garden-Robinson said.
“The reason we do all of this is to stave off the clostridium botulinum, which produces a deadly toxin,” she said.
Extension Service experts conduct research on canning every five years, so if people who are canning are using old cookbooks for recipes, they should compare them with the service’s newest recommendations, Garden-Robinson said. For example, if proportions in the old recipe are different than the new recommendation, cooks should use the latter.
Besides using tested recipes, cooks also should heat the jars of produce to the proper temperature and use the right equipment to can it. Using short-cut methods — such as dishwashers, instant pots and microwave ovens — to heat the jars is not safe, Garden-Robinson said. Instead, depending on whether produce is low acid or high acid, jars should be processed in a boiling-water bath canner or a pressure cooker.
Cooks also should make sure the equipment they are using is in good condition.
“You really have to look over your equipment before you begin,” Garden-Robinson said. For example, pressure cooker gauges should be checked annually. Many county Extension services will test the pressure gauges, free of charge, she said
This year, gardeners who are canning may notice a shortage of lids and be tempted to use paraffin or to re-use old lids to seal jars of produce.
Neither can be substituted for a new lid. Even though gardeners’ mothers or grandmothers used paraffin to seal jars, it’s not safe because the paraffin could have a pinhole crack that lets bacteria seep in, Garden-Robinson said. Used lids, meanwhile, may not seal properly.
Though canning may seem like a difficult, time-consuming project, it’s really not, she said.
“Just follow the directions. Go to an Extension site. We have everything you could ever need,” Garden-Robinson said.
And if it seems like an impossible undertaking — or if lids aren’t available — there are other ways to preserve food, Driessen noted.
“Start out with freezing or drying,” she said.
“You can freeze almost anything,” Garden-Robinson noted. “If you can’t find lids and you have freezer space, I would efficiently load my freezer so I could get my product in there.’