The 7 Most Horrible Canning Mistakes to Never Ever Make

Canning food at home is a great way to increase your food security, and it’s also a rewarding hobby. Having a pantry full of canned fruits, veggies, meats, and more can make for easy meals and keep your family fed during times of trouble.

And even if you’ve never done it before, it’s pretty easy to get started. Whether you’re using a water bath canner or a pressure canner, the principles for preparing a recipe and processing it correctly are straightforward and simple.

But just like everything else, the devil is in the details. Some canning mistakes will only cost you time and resources, but some can be downright deadly! You’ve got to avoid these at all costs. Keep reading, and I’ll tell you about seven horrible canning mistakes you can’t afford to make.

❌ Not Following Altitude Adjustments for Recipes

This is an easy mistake to make, especially if you’re grabbing old recipes out of a family recipe book or from random places on the internet. Whether you are using a water bath or pressure canner, your altitude makes a big difference when it comes to properly processing your jars.

No, this isn’t some niche situation where you would be canning in an aircraft or something like that; I’m talking about your altitude above sea level.

The closer to sea level you are, the shorter the processing time. Inversely, the higher your altitude above sea level, the longer the processing time.

That’s because water boils at a lower temperature at higher altitudes. Usually, you’ll only add 5 minutes for every few thousand feet you go above sea level, but it’s recipe-specific, and you’ve got to pay attention.

If you’re using a water bath canner, you’ll simply add more processing time so your food is thoroughly heated. If you’re using a pressure canner, you’ll turn up the pounds of pressure instead. If your recipe doesn’t have an altitude adjustment, check a different source to confirm.

❌ Failing to Test Pressure Gauges

This is a big one that I myself am guilty of. Any pressure canner that uses gauges or other instrumentation must be properly maintained for safe, reliable function. Part of that maintenance is getting the gauges tested. An accurate gauge is the only way you’ll be able to properly assess the status and timing of your jars.

For instance, you are only supposed to start the processing timer on a batch of jars once the pressure reaches, and stays at, the designated level.

If your gauge is short, meaning it reads a few pounds higher than it actually is, you might process an entire batch of jars under inadequate pressure, meaning that temperatures were insufficient to eradicate harmful bacteria and prevent food poisoning.

Something else you’ve got to ensure when using a pressure canner is that it stays at the required pressure for the entirety of processing. If the gauge is a little sticky or reads too high, the pressure might drop below safe levels unbeknownst to you.

This is really serious: bad gauges are a great way to wind up horribly sick or even die. Coming down with botulism is quite likely under these circumstances.

❌ Processing Jars in an Oven

This is one of the most persistent and troubling canning mistakes I see over and over again. Some people persist in trying to process jars in the oven. It’s usually done, or irresponsibly recommended, as an alternative to water bath canning. This is a bad idea for a host of reasons…

The scientific reason is that air does not transmit heat as readily as liquid, and that means that heating of the jar contents occurs less evenly and also more slowly.

Trying to use an oven with the processing time recommendations for a water bath recipe is almost certainly bound to fail. And you know what that means: spoiled food at best, or food poisoning at worst.

Another safety issue is more prosaic: typical canning jars are indeed resistant to high heat, but only when used as directed.

Placing them on an oven rack or other oven cookware and heating them dry is likely to result in cracking or even bursting. That will make a huge mess, but it could also mean you get severely cut.

I don’t care what anybody says, and I don’t care how your great-great-grandma used to do it: canning in an oven is not safe!

❌ Not Processing Packed Jars Swiftly

The lion’s share of good canning procedure is paying attention to detail and timing…

Timing, as we learned, is important for processing; food must be processed for a specific interval and not a minute less. But timing is also important when it comes to getting prepared food into the jars and then into the canner for processing.

For my recipe walkthroughs that I’ve posted here, I always emphasize in the instructions that readers need to execute some steps swiftly.

Specifically, when hot packing, the piping hot food needs to go into hot, freshly sterilized jars, get capped, and then go into the canner immediately.

This is crucial because the food needs to stay hot so that when processing begins, the total time spent at the processing temperature is correct.

If you lollygag or get distracted and let the food cool down before it goes into the canner, that can interfere with the process and allow certain bacteria to survive.

Most worryingly, Clostridium botulinum, the nasty little bugger that secretes the toxin that causes botulism. If you’re lucky, it’ll just send you to the hospital, but if you’re not… it can kill or cripple.

Jars should always be preheated, and whether you are hot packing or not, filled jars should go into the canner and be processed at once.

❌ Thickening a Recipe with Flour, Etc.

Another mistake, and another potentially deadly one, I see beginners make from time to time.

Whatever you are canning, you can’t add any additional thickeners: I’m specifically talking about starch, flour, cornmeal, etc. Any thickening that occurs as the result of pre-cooking, the addition of pectin, or any other ingredients called for by the recipe are fine.

This is because the thicker the contents of a jar, the slower the rate of heat penetration into the food itself.

This can, once again, lead to insufficient processing, which can allow germs to survive and subsequently flourish. This, as we’ve learned, is absolutely disastrous, so I won’t belabor the point.

Typically, folks will make this mistake when canning soups, broth, sauces, and the like. Don’t do it! No matter what you are preparing, you can always thicken it after you decant it for preparation.

❌ Adding Extra Ingredients to Salsas, Soups, and Sauces

Speaking of soups and the like, don’t get creative with the ratios of ingredients: published and approved recipes from authorities like the NCHFP and various major university extensions are relentlessly tested for repeatable, reliable, and safe preparation.

Where people go wrong is assuming that they can fudge the recipe ratios a little bit. Sometimes this is true, but when it comes to certain ingredients like peppers, chilies, onions, and other veggies, this can go horribly, horribly wrong.

That’s because these added veggies can cut the needed acidity to safely process these products. Insufficient acidity is a leading cause of spoilage and food poisoning.

Always review recipes carefully to see what you can, and more importantly, what you can’t, change to your taste.

❌ Improvising a Recipe

The last mistake on our list is the crowning one of them all: making up or improvising a canning recipe.

You must never, ever, and I mean ever, do this! Like I mentioned above, published and approved canning recipes from trusted authorities have been tested over and over again for safety, with a built-in margin for error.

There are tons of great recipes out there, and one of the most enjoyable parts of the home canning process is trying new ones and figuring out your favorites.

The temptation is oh so strong to come up with your own: your own spin on a pie filling, a can-able version of your favorite soup, easy mixed veggies, or anything else.

This is like roller skating in the dark with knives taped to your hands: it’s going to end in disaster sooner or later. When you improvise a recipe, you’ve got no way to know how long the food must be processed, and under what conditions, for safety.

You won’t know if the pH level is okay. You won’t know if any ingredients will interfere with any others or cause problems with processing.

It’s the worst kind of gambling, and made even worse by the fact that it might go okay once or twice. Just remind yourself that it might be someone you love who pays the price for your hubris, and not you…