5 Tips for Freezing Food In Glass Jars + Mistakes To Avoid

Looking to freeze food in glass jars? Here are all my top tips and the mistakes to avoid to prevent sudden breakage.

If you’re looking to store your food sustainably, glass is a good place to start. It’s endlessly recyclable and a great way to reduce your reliance on plastic in the kitchen, whilst keeping your food fresh. And glass is surprisingly versatile – you can even store food in the freezer in glass jars and containers.

However, it’s not quite as straightforward as chucking your leftover soup in an old jar and popping it in the freezer. Without some forward planning, you could have a broken jar on your hands and worst of all – no soup! As someone who loves a good bowl of soup now and again, that would be a total disaster!

The good news is that there are just a few golden rules for freezing food in jars, that if you can follow, can completely avoid any glass-based incidents.

Here’s all you need to know to avoid breakages:

How To Freeze Food In Glass Jars Safely

Make Sure Your Food Is Fully Cooled

Temperature changes can really stress glass. Taking a jar that’s warm and putting it straight into the freezer can make that glass crack faster than the blink of an eye.

As such, it’s always a really good idea to let food cool completely before putting it into the freezer. Once your food has cooled to room temperature, you can portion it into jars, and then freeze it safely.

Use A Wide-Mouthed Jar

Not all jars are created equal when it comes to freezing. You’ll want to look for jars with straight sides and wide mouths. These types of jars help reduce the chance of cracking because there’s less pressure from expanding food. This makes them an altogether safer choice.

Jars with “shoulders” (those sloped bits at the top), like ketchup bottles or drinks bottles, are more likely to break when filled with liquids. This is because there’s less room for food to expand when it freezes. As such, it’s best to keep those for dry ingredients or fridge storage only.

Don’t Overfill The Jar

When you are storing foods in glass, it’s very important to remember that liquids expand when they are frozen. And unlike plastic, which can expand a little or a lot depending on the container, glass is rigid. This means glass has zero wiggle room. If your liquid expands and it’s got nowhere to go then you can be sure that your jar will break.

Consequently, when you are freezing food in glass jars, particularly soups, sauces or liquids like oat milk, it’s important not to completely fill the jar. Instead, give your liquids a little breathing space – around 3 to 4 centimetres is ideal – at the top to help avoid your jar shattering or breaking.

If you’re freezing something more solid, such as nuts (what, you don’t freeze nuts?!), chopped fruit, or seeds, then you don’t need to worry about headspace quite so much. These won’t expand in the freezer, so your jar is less likely to come a cropper.

Place The Lid On Loosely

Once you’ve portioned your food into jars, it’s really important that you don’t screw the lids on too tightly at this stage. Just rest them lightly or use a loose-fitting lid if you can. This allows the food inside the room to expand without building up too much pressure.

Once your food is completely frozen, you can then tighten up the lid. If you forget to tighten up the lid (I often do!), then don’t worry, it won’t affect your food.

Be Careful How You Stack

It’s also important to watch how you stack your jars to prevent jars from falling out of the freezer. This won’t be much of a problem if your freezer has drawers, but if not it’s important to play it safe. Freezer Tetris is not the aim of the game here!

Keep them upright in a safe spot where they’re not going to fall, with a little space between each one, especially if they’re warm or freshly filled. This allows the air to circulate, and allows them to freeze efficiently.

How To Defrost Frozen Food Stored In Glass Safely

Freezing your food isn’t the only bit where breaks can occur. Sometimes cracks can happen during the defrost stage. So it’s really important to avoid sudden temperature shifts.

Start by transferring the jar from the freezer to the fridge. Let it sit for several hours or overnight. This slower thaw prevents stress fractures in the glass.

Whatever you do, do not put the jar in water, in the microwave, or on a hot surface, like a radiator to defrost. As tempting as it is to speed up the defrosting process, it can cause thermal shock which can cause the jar to break.

The Best Jars For Freezing Food In

Some brands like Kilner make jars specifically labelled as freezer-safe, and these are a good option if you’re buying new. But repurposed jars can work just as well if you’re cautious. Just give them a good check over first – any chips, cracks, or scratches make them more vulnerable to breaking under stress.

I don’t buy specific jars for freezing food in. Instead, I re-use what I already have. Jars that I have found particularly useful are old peanut butter jars and vegan mayonnaise jars. I also like jam jars for freezing single portions of soup and sauces.

Other Top Food Storage Tips

Looking for more sustainable food storage top tips? I’ve got you covered:

• If you’re having a clear out, then here’s what to do with old plastic food storage boxes.
• Here are some sustainable alternatives to cling film.
• The foods you didn’t know you can freeze (number 7 is a game changer!).
• And here are some clever tips to make fresh food last longer.