10 dos and don'ts for canning garden tomatoes and vegetables safely

Emily Teel
Salem Statesman Journal
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The OSU Extension Ask an Expert hotline is again open for all your food preservation questions. Here's a look back at some tips from last year on saving your garden's bounty.

August is the time that tomatoes, beans, summer squash, beets, carrots and cucumbers ripen in gardens and begin arriving at farmers markets. Save some summer sunshine by pickling, drying, freezing, or canning these seasonal fruits and vegetables to enjoy in the rainy months ahead. 

While the quality of foods preserved by drying or freezing might vary, there is little danger of them doing harm. Canning, however, if done improperly, can create an environment where a particular type of bacteria can thrive, producing botulinum toxin. This toxin is the source of botulism, a type of poisoning that can cause paralysis. 

Following a few food safety protocols will ensure that your home-canned foods remain safe, nutritious and delicious. If you're a novice to home food preservation, consider taking a class to give you a solid foundation. Experienced canner? Consider the following a refresher course. 

DO be aware of the difference between water bath canning and pressure canning

The general rule is that certain foods, those high in acid (with a pH of 4.6 or lower), can be safely preserved in a water bath or steam canner. This includes pickles, sauerkraut, and most fruit preserves including jams, jellies, marmalades, and certain fruit butters. Low acid foods (those with pH values higher than 4.6), conversely, must be preserved in a pressure canner to be safely stored at room temperature. They include red meats, seafood, poultry, milk, and all fresh vegetables except for tomatoes.


DON'T use a pressure cooker to can food

Both a pressure cooker and a pressure canner operate on the same principle of using pressure to increase the temperature inside. Even so, you shouldn't try and use the same pressure cooker you would use to make pot roast or beans to pressure can. Pressure cookers may not maintain adequate pressure to safely treat preserves. The one exception to this rule is a recent generation of electric multi-cookers, including the Instant Pot Max, which includes proprietary settings for canning under certain, specific parameters. 

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DON'T try and can just any recipe

Recipes for jams, jellies, pickles and salsas abound on the internet and in collections of family recipes, but that doesn't mean that they're safe for canning. While sugar and salt each act as preservatives in canned goods to a certain degree, the pH of the finished product is the key determinant of whether or not the finished product will be safe. A recipe for tomato salsa, for example, may yield tasty results but not be acidic enough to safely can. Unfortunately, this includes historic recipes passed down from grandmas, too. For home canning, seek out recipes from trusted resources including the National Center For Home Food Preservation, the Oregon State University Extension Service, and published cookbooks. 

Jars of pickles out of boiling water.

DO pre-warm your jars

When canning it's not necessary to fully sterilize your canning jars before filling them. The processing step (either in boiling water or under pressure) once they are filled and sealed sterilizes their contents. That said, the jars should be clean (and free of chips). Both they and the food going into them should be hot. You can do this either by running them through a dishwasher on a hot/sterilize cycle or warming them for five minutes in simmering water. This step will prevent jar breakage during processing caused by thermal shock.

DON'T boil your jar lids

Just as jars don't need to be boiled before canning, you shouldn't boil your canning lids either. Ball and Kerr, manufacturers of canning lids with a built-in gasket, recommend simply washing them with warm, soapy water and keeping them at room temperature until you're ready to wipe your jar rims and seal your jars. 

Lids for canning jars.

DO pay attention to processing times

Just because a jar lid creates a vacuum seal does not ensure food safety without proper processing. Processing, the step of boiling or pressurizing jars filled with food, is the active step. Pay attention to processing times for the specific food and the specific jar size you're canning. In water bath canning, start the timer once the canner returns to a boil with sealed jars submerged (by at least an inch of water). In pressure canning, start the timer once the pressure gauge reaches and maintains the recommended level. Experienced canners can download OSU's free Canning Timer and Checklist app to either Apple or Android devices to help track processing times. 

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Home Canning Preserves.

DO ask for help if you need it

In all things food-preservation, it's better to err on the side of caution. But if you're unsure of how to interpret a recipe or need some help troubleshooting your canning project, there's an Oregon-based resource to offer help. Call OSU Extension's Food Safety & Preservation Hotline hotline at 800-354-7319 to talk through your question with certified Master Food Preserver volunteers. The hotline is live until Oct. 18 from 9 a.m. to 4 p.m., Monday through Friday.

DON'T store your canned goods with rings on

Once your jars have completely cooled post-processing, remove the canning rings. If any jar lids aren't tightly sealed store them in the refrigerator and use them first. The reason behind storing jars without their rings is that spoilage within the jar will cause gas capable of popping the lid off as long as there is no ring on it. Keeping the rings on can mask these signs of spoilage. 

Refrigerator pickles are easy to make because they bypass the boiling-water bath canning process. The cucumbers rest in a brine of vinegar, sugar water and spices.

DO label and date everything 

Just a few batches of jam into the canning season and it can already be difficult to remember whether those dark purple jars contain plums, blueberries, or barbecue sauce. Label and date everything, either with a marker directly on the jar lids, masking tape, painter's tape, or cute custom labels. This will ensure that you can use the oldest things first and keep things rotating. 

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DO inspect your jars before using the contents

When you're ready to use your home-preserved foods, take a good look for signs of spoilage. Metal jar lids should still be firmly attached and either flat or curved slightly inward. There should be no signs of leakage. As you release the metal jar lid (a handheld bottle opener works well), notice whether there is an in-rush or an out-rush of air.  Air rushing in as an indicator of a jar with a good seal. Air or liquid rushing out is an indicator of spoilage. Smell the food; the aroma should be consistent with when you canned it. 

Level up your canning confidence by taking a class:

Check out OSU Extension Service's full schedule of events: https://extension.oregonstate.edu/program/all/mfp/events


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