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Freezing mason jars safely

Freezing mason jars safely

Reviving the lost art of self-reliance, one small step at a time

Canning jars are a favorite plastic-free method of food storage for a lot of people, but what about freezing mason jars? Can you freeze in mason jars? Yes, you can, but there are some guidelines for safety that you should follow.

3 glass jars with frost on the outside and white plastic lids

Mason jars are the go-to for home canning recipes, but they can also be used to freeze food. Surprisingly, this is a bit of a contentious subject. Some people won’t even consider the idea of freezing mason jars. They’re just too worried about breakage.

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Does glass break in the freezer? 

Not automatically. Glass jars won’t just explode in the freezer. What causes glass to break in the freezer is the expansion of the food stored in glass as it freezes. If there’s not enough space to allow for that expansion, the food will push against the glass, causing breakage.

I’ve been freezing food in glass jars for years upon years and in all that time I think I’ve had three break. Each time? It was my fault for not following safe practices.

What happens when a jar breaks?

In my experience, a jar that does break in the freezer will simply crack in several places, but retain its shape. If you find a broken glass in the freezer, remove the jar carefully and transfer it to a bucket or bowl and allow the contents to thaw. Once thawed, you can safely dispose of the pieces of glass that remain and trash the rest. I’d avoid composting it, just in case any fragments of glass remain.

What can you freeze in mason jars? 

As long as you follow the guidelines laid out below, you can freeze most things in glass jars. Freeze smoothies so they’re ready to grab and go for lunch. Freeze bone broth, homemade soup, chili, or fruit juice. You can freeze cooked beans to have them ready for adding to meals or making hummus. You can freeze fresh berries or pesto. And you can even freeze homemade jams and jellies.

Mason jars are an environmentally sound option for food storage and are perfectly suitable for freezing food. You just need to follow some simple safety guidelines.

While you can freeze glass, opt for mason jars out of an abundance of caution. Reuse glass jars from the supermarket for storing bulk dry food, not freezing. Mason jars have thicker glass and are sturdier than recycled jars.

To prevent breakage, your best bet for freezing jars is to use straight-sided mason jars. This allows the food inside to shift upwards as it freezes. Jars with “shoulders” impede that movement and are more likely to break when frozen. These straight-sided jars are available in 4 ounce, half-pint, pint and 24 ounce sizes.

empty mason jars with metal lids (3)

This is key! If you fill the jar all they way to the top, put a lid on it, and pop it in the freezer, that expanding food has nowhere to go. That’s how breakage happens. The trapped food expands and pushed against the glass until it breaks.  The National Center for Home Canning suggests 1/2″ head space for pint sized jars no matter what you’re freezing. For quarts, they suggest a 1″ head space for liquids and 1/2″ for “dry pack” items like fruit without liquids or nuts.

I tend to be even more conservative when I’m freezing food in glass, and rarely use less than an inch of head space, and more like an inch and a half (or two!) when freezing liquid in quart jars.

If you’re freezing in mason jars with shoulders because that’s all you have available, measure the head space from the shoulder, not the rim of the jar.

frozen food in glass jars

You’ll want to avoid temperature extremes when freezing food in glass. Don’t put warm jars directly into the freezer. Instead, put jars of broth or soup in the refrigerator overnight, then transfer to the freezer.

I know, we’re trying to use less plastic when freezing our food. And this is not a safety issue as much as it is a cautionary tale. Metal lids and rings will work fine for sealing the jars, but they do tend to rust when used as freezer storage, eventually becoming unusable. Plastic lids have no such problem and they can be reused over and over again. In the end, I feel like this is the better use of resources.

In other words, plan ahead. The one drawback to freezing in glass is that the food inside is not readily available. If you need a jar of broth for a recipe, you’ll need to thaw it out ahead of time. You may be tempted to run the frozen jar under a stream of warm water to hurry up the process, but restrain yourself. Exposing mason jars to temperature extremes when they come out of the freezer can cause breakage.

To safely thaw frozen jars, set them on a towel at room temperature. The towel will absorb the liquid that condenses on the outside of the jar as it thaws, saving you a mess.

Once the contents are mostly thawed, transfer to the refrigerator or add to your recipe.

frozen mason jars

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Kris Bordessa founded Attainable Sustainable as a resource for those striving toward a simpler, more self-reliant lifestyle. She is continually learning, often thanks to this virtual community.

AvatarCarol L

Just a note about the plastic lids: they are NOT airtight! If you don’t believe me, just put some water in a jar, put a plastic lid on and shake: it will leak. I keep forgetting this, and when I go to shake something I have thawed out that is liquid, it always leaks on me, and actually, quite a bit! SO frustrating. My guess is that they won’t keep foods as long due to air getting inside and we all know that air ruins frozen foods. Just something to keep in mind.

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Kris BordessaAloha! I’m Kris Bordessa, writer and hobby farmer, gardener and canner, chicken wrangler and eternal experimenter. Here at Attainable Sustainable, I aim to encourage readers — that’s you! — to embrace a more self-reliant lifestyle, one small step at a time. My latest book, ATTAINABLE SUSTAINABLE: The Lost Art of Self-Reliant Living, will be published in 2020 by National Geographic Books. Read More…

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