The Biggest Canning Mistakes You’re Making

Here’s how to make sure your homemade canned food is safe and delicious.

October 3, 2016
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In mid-winter, when your garden is buried in snow and all the farmers' market has to offer are potatoes and rutabagas, there's nothing quite like the feeling of having tasty, organic food you made yourself available in your pantry. I’ve been fascinated by preserving food in jars since I was a small child and helped pick the wild berries my mother turned into jars of jewel-toned jelly that we enjoyed all year. In high school when my friends were buying boy-band posters, I bought canning jars and a pressure canner and then built shelves in the basement to store my bounty.

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Whether you want a few jars of jam or aim to store a year’s worth of veggies and fruits—canning is a safe and easy way of creating foods that can be stored at room temperature. That said, you do need to follow some simple rules to keep it safe. Here are 27 of the most common canning mistakes—and how to avoid them.

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1. Canning Grandma's Favorite Soup

Unless you want to risk a nasty case of the food poisoning called botulism, stick to current, professionally tested recipes and instructions from the USDA, the National Center for Home Preservation, or a State Cooperative Extension Service. My go-reference is the free and frequently updated online Canning Guide by the University of Georgia. Make and freeze Grandma’s soup—or pretty much anything else that tickles your fancy—but don’t can anything unless the recipe is in an approved guide that was published in the past 10 years.

Related: 8 Gardening Mistakes You Make Every Fall

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2. Tweaking Canning Recipes

I’m an inventive cook—I love to try new recipes and adapt old ones by substituting what I have fresh in the garden or available in the pantry (here's how to tell when your pantry items have gone bad). But not when I’m canning. Tweaking canning recipes may change how fast the food heats during processing, possibly leaving areas where Clostridium botulinum spores may lurk—it's just not worth the risk.

There are only a few exceptions to this rule: You can add small amounts of seasonings and adjust salt quantities—or even skip salt entirely—in anything except fermented products. You can adjust sweetener quantities—or skip sweetener—in anything except jams, jellies, or preserves, and you can also add extra vinegar or lemon juice. Never, however, reduce the amount of vinegar or lemon juice in a canning recipe.

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3. Doubling Jam Or Jelly Recipes

Products that need to jell can be temperamental and doubling a recipe can cause the batch not to set up. Make two batches for best results.

Related: 5 Easy Jam, Jelly, And Preserves Recipes

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4. Using Artificial Or Low-Calorie Sweeteners

You can’t reduce or replace sugar with a low- or no-calorie sweetener in a standard jam or jelly recipe, as the sugar is a critical component in the jelling process and shelf life. You can reduce, omit, or replace caloric sweeteners in other foods, but have a care when making substitutions: During processing, saccharin-based sweeteners turn bitter and aspartame-based sweeteners lose their sweetness (take a look at the 5 worst sweeteners you can have in your kitchen). Stevia is stable to heat and can be used in canning, but the final flavor can vary, so make a small test batch first.

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5. Not Checking Jars For Nicks, Cracks, and Scratches

Even a tiny chip on the top surface of a jar rim can prevent the lid from making a good, long-lasting seal. Run your finger around the rim and check before using a jar for canning. Also hold the jar up to the light and check for cracks or scratches, as those can lead to breakage during processing and wasted food.

 
 
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6. Using Jars and Lids Right Out Of The Box

If your recipe says to pre-sterilize the jars and lids before you fill them, do it. Ten minutes in boiling water kills any stray nasties that might be lurking on the inside. Here's one exception to this rule: If your recipe calls for pressure processing for more than 10 minutes at 10 pounds or more, you can skip pre-sterilization. You might want to do it anyway, though, since submerging jars in hot water until just prior to filling them with hot food reduces the risk of jars breaking. While you're sterilizing your jars, check out the 5 pieces of mason jar trivia that will get you in the mood for canning.

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7. Not Wiping Rims Clean

No matter how careful I am, I always get at least a bit of food on the top edge of some of the jars. Even a teensy-tiny speck of food caught there can prevent the lid from making a good, long-lasting seal. Wipe each rim with a clean, moistened towel just before placing the lid on it.

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8. Leaving Air Bubbles

Excess air trapped under or in the food can cause poor seals and spoiled food in storage. Release it before placing lids on.

 
 
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9. Not Pricking Your Cucumbers When You Make Whole Pickles

Pricking whole fruits and veggies all over with a fork before pickling helps insure your final pickles will be crisp and flavorful, not soft or limp. (Check out these 6 veggies you never knew you could pickle.)

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10. Using Iodized Table Salt

Salt with added iodine can lead to discolored and limp final products. This is especially true for pickles.

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11. Treating Reusable Lids Like Single Use Lids

If you use reusable canning lids such as Tattler Lids, be sure to follow the instructions that come with them rather than the ones in standard canning guides. Properly used, these BPA-free lids are safe and effective—and they'll also save you money in the long run, too—but they often won’t seal if you don’t follow the correct procedure. Along with reusable lids, here are 5 essential canning tools you need.

 
 
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12. Canning In Mayonnaise Jars and Other Single Use Jars

Don’t even think about trying to can in them. Yeah, I know Aunt Alice used them for decades. But jars you buy food in at the supermarket are too thin to survive repeated processings and often break. Why risk wasting your food and creating a nasty mess to clean up? Stick with genuine mason jars for your canning.

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13. Over- Or Under-Filling Jars

Too much or too little headspace—the space between the food and the rim of the jar—can cause lids not to seal properly. 

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14. Using Less-Than-Prime Produce

Canning is a great way to use up produce that's delicious but not pretty. But it will not salvage underripe, tasteless, or overripe fruit. Remember, your finished food will only be as tasty as it was going in. 

 
 
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15. Using A Water Bath For Low Acid Foods

Remember our nemesis Clostridium botulinum? Its spores are very, very heat resistant—even hours in a boiling water canner will not kill them. Unless a food is very, very acid (pickles) or has loads of added sugar (jelly, jam), the airless conditions in a sealed jar stored at room temperature are the perfect place for those surviving spores to germinate and proliferate. Yes, it’s rare. And yes, you may know lots of people who use a water bath without problems. But it can happen. And worst of all, food containing botulism looks and smells fine, so you won't know until it's too late. Don't risk it: Use only current approved recipes, and follow the instructions exactly. 

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16. Using The Oven, Microwave, Dishwasher, Vacuum Sealer, Or Canning Powders

You can find scads of sketchy advice for using any number of alternative canning methods. None of these methods consistently kill spoilage bacteria, let alone Clostridium botulinum spores. Don’t use them.

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17. Assuming A Sealed Jar Means The Food Inside Is Safe

Jars seal when the pressure inside is lower than the air pressure outside. To be safe from spoiling, the food inside the jar must have been processed for a sufficient time at a high enough temperature with the lid in place to sterilize the food. Then, and only then, will the seal keep the food safe at room temperature by shutting out any new spoilage organisms and oxygen.

 
 
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18. Processing A Few Jars In Your Pressure Cooker

Pressure cooking is a great way to save time and energy, but because a small cooker heats up and cools down much faster than a full-sized pressure canner, foods may not stay hot enough, and for a long enough time, for safe canning. Stick with approved recipes and full-sized pressure canners.

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19. Not Adjusting For Altitude

If you are more than 1,000 feet above sea level, you need to increase times, pressures, and temperatures as recommended in a current canning guide. Water boils at a slightly lower temperature at higher elevations and the difference can be enough to change the reliability of instructions.

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20. Cranking Up The Pressure

If you're not adjusting for altitude, don’t assume more pressure is better—or, worse, faster. Food may overcook and discolor or may not be sufficiently processed.

 
 
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21. Allowing Pressure To Yo-Yo

Fluctuating pressure during processing can blow liquid out of your jars, making a mess, wasting juices and food, and leading to jars that don’t seal properly. Keep pressure steady throughout processing. (Make applesauce in minutes with your pressure cooker!)

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22. Leaving The Jars To Cool In The Canner

Turning off the heat doesn't mean your canning is complete. You'll need to follow the instructions for cooling and removing the jars from the hot water bath or the pressure canner. Otherwise, jars may seal poorly and unseal in storage, leading to spoilage.

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23. Putting Hot Jars On A Cold Counter Or In A Draft

Rapid changes in temperature can cause jars to shatter. Find a draft-free place, and gently place hot jars on a padded surface (you can use a folded towel to create padding). Allow jars to cool completely before moving.

 
 
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24. Not Having The Right Tools

Besides suitable jars, lids, and a kettle or pressure canner, you should definitely invest in a jar lifter, a special set of tongs for lowering jars into the canner and lifting them out again. A canning funnel is also handy—it makes filling jars easy, and I also use mine all the time to put leftovers into jars to store in the fridge.

jam
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25. Being Impatient With Jams and Jellies

Not all recipes and batches “set up” immediately. Let jarred jams and jellies sit undisturbed in a cool place for two weeks before concluding they are going to remain liquid. If your jarred jams don't set, you can either use them as syrup or remake them.

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26. Storing Food In Hot, Sunny Conditions

Canned food is really pretty, but it will fade and soften if exposed to light and heat for extended periods of time. And while these canned goods will still be safe to eat, they won’t taste as good. Your best bet is to keep your canned goods in a cool place out of direct sunlight. (Check out these 10 things you're storing in the wrong place.)

 
 
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27. Not Washing Metal Bands After Jars Are Cooled Down

During canning, bits of food and traces of dirt can get expelled and end up trapped under the metal band. This can lead to rust, reducing the lifespan of the bands. More importantly, this rust can spread and eat through the jar's lid, allowing food to spoil. Once the jars are completely cool, remove the metal band and test the seals—each lid should be concave and sealed so tightly that you can't lift the lid away from the jar with your bare hands. Next, wash the outsides of sealed jars and every loose metal band in warm, soapy water. Dry jars and bands completely. Store bands for your next canning adventure, or, if you prefer, screw them back onto the jar.