These jars aren’t for canning

Photo by Sarah Walker Caron

My mother texted me earlier this week with an urgency: could the flat lids from canning jars be reused? She’s a novice canner who has loved the jams, relishes, sauces and pickled items I’ve canned over the years, but only just dipped her toes into canning too.

I think sometimes experienced canners forget — or don’t realize — that not everyone grew up canning. My mother, who grew up in the 1960s in New York, or I, who grew up in the 1980s in New York, certainly didn’t. So things that might seem trivial — or obvious — aren’t.

She is learning, slowly, from me. I learned by sheer will, relying on books like “Preserving Summer’s Bounty,” by Susan McClure and “Preserving Memories,” by Judy Glattstein to learn to first make jams, then pickles, then relishes and sauces. At first, I primarily water-bath canned to preserve, but these days, I also freeze vegetables like string beans, peas and corn in vacuum-packed bags. (Some vegetables need to be blanched before freezing.)

You’ll notice that I didn’t mention pressure canning. I don’t pressure can presently. A combination of water bath canning and freezing is perfect for me right now. That could change in the future, of course. 

All of this, and an email from a reader, got me thinking about the things we take for granted as canners. 

For instance, I have always been drawn to the marinara jars modeled after actual canning jars. It would be easy to assume that because they look like canning jars, they can be used as canning jars.

They can’t.

“There are a lot of beautiful jars out there. The spaghetti jars are made to look like canning jars [but] those jars are not tempered to be used for multiple cannings,” said Lisa Fishman, a regional supervisor and nutrition education professional with the University of Maine Cooperative Extension.

What does that mean? They won’t hold up to the high temperatures of a water bath or pressure canner. Using them risks breakage.

“Jars that are not tempered property are more likely to be cracked or shattered under pressure,” Fishman told me.

So, if you’ve been stocking those jars away like I do, scratch “can stuff” in them off the list of potential uses. The good news though? They still have plenty of potential uses. 

For instance, those jars work well for refrigerated leftovers or freezing items (don’t forget to leave headspace for expansion when liquid freezes into a solid). So if you freeze your marinara sauce like I do, then you can spoon it into one of those jars leaving plenty of headspace and stick it in the freezer. They also work well for storing foods in the fridge. Why not reuse one to hold that coleslaw you made for the weekend? Or pack your salad in it for lunch (You might want to bring a bowl to dump the contents into). 

Aside from food, jars can be repurposed to hold other stuff. My grandfather put spare screws and nails in some. My daughter has transformed several into pencil jars and ponytail holder storage. Or collect several and divide craft supplies into them.

But what about antique canning jars? Growing up, we had those all over the house — often holding hair ties and barrettes or cotton balls. But, it turns out they can still technically be used for canning if you purchase new seals for them.

Still, those classic hinge-top jars aren’t universally recommended. Fishman said that the cooperative extension steers canners away from them for canning use.  

“The old canning jars that we used to use are pretty but we also know that those run a much higher risk of broken seals,” Fishman told me. These jars, which I’ve inherited a few, are also good for freezing. 

Plus, she said, it’s getting harder to find the rubber gaskets needed to can with them.

She recommends using those jars for dry goods. You will need a rubber gasket (as you would also for freezing), but you don’t have to worry about a poor seal.

So stick to modern canning jars.

Photo by Sarah Walker Caron

As for my mother’s question, my answer was simple: No, you can’t reuse a flat lid to can again but they can be used for storing foods in the fridge or freezer. 

Fishman agreed with that advice. “The flat lid is a one time use for canning. You can keep a few [used ones] on hand to use in the freezer or refrigerator,” Fishman said. 

My advice: make sure you mark the used tops too to avoid accidental reusage.

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