While it’s always fun to make homemade jams and sauces to store in the freezer for later, they don’t always emerge from the freezer unscathed. More often than not, frozen glass jars tend to crack or break, especially as they start to thaw. So, what’s the right way to freeze food in glass jars?
To freeze food in glass jars, use jars that are made with tempered glass and have straight sides. Don’t fill the jars right to the top, and don’t tighten the lid all the way if the contents aren’t 100% frozen. Leave some space between the jars and thaw the contents as slowly as possible before use.
In order to avoid a jam or sauce explosion in your freezer, let’s take a closer look at whether you can put a glass jar in the freezer in the first place and the measures you can take to prevent it from breaking. We’ll also look at why we’re using glass in the freezer, and not something else like plastic containers.
Can You Put a Glass Jar in the Freezer?
Yes, you can put a glass jar in the freezer — but you’ll have to make sure that you use the right kind of jar. You’ll also have to take some precautions to prevent the jar from breaking.
Here are the steps to take:
Get the Correct Shape
Glass jars come in two kinds: those with shoulders and those with straight sides. When it comes to freezing, the latter is the better option.
As you might have guessed from the name, jars with straight sides (on Amazon) are completely straight from top to bottom.
In other words, the jar’s opening isn’t bigger or smaller than the jar and the jar itself doesn’t bow outward or inward. This is the one you want for freezing.
Meanwhile, glass jars with shoulders are those that have an opening that is larger or smaller than the jar itself. The “shoulder” is essentially the part that bends outward or inward between the widest part of the jar and the mouth.
Get the Right Kind of Glass
Glass jars are made with either non-tempered or tempered glass. For freezing, you should choose the latter.
Non-tempered glass has microscopic air bubbles that contract and expand as the glass cools or heats up, particularly at extreme temperatures. As these air bubbles expand, the glass cracks and, in some cases, even explodes.
Meanwhile, there are no air bubbles in tempered glass because the glass is strengthened in the manufacturing process. As a result, a tempered glass jar is nearly 4-5 times stronger than regular or non-tempered glass.
While you can freeze non-tempered glass, using tempered glass reduces the chance of your jar breaking in the freezer.
Leave Space for Expansion
The space from the fill line to the jar’s lid is known as the headspace. As food freezes, it tends to expand, and the only place it can go is the space you’ve left at the top of the jar. So, when freezing anything in glass jars, always be sure to leave enough room at the top.
Generally, one inch of headspace should suffice. But if you have a bigger jar with more food to freeze, it’s going to expand more, which means you should leave more room accordingly.
Also, note that skinny jars require more headspace compared to wide jars.
Store Jars Horizontally
In addition to leaving some headspace, you can also store jars horizontally (on their side) to leave enough space for expansion.
When storing the glass jar vertically, the contents only have around 2-3 inches of space for expansion. But when you store the jar on the side, you have the whole length as well as 2-3 inches of depth.
Of course, storing jars on their side takes more room, but you can turn them upright after they’ve been in the freezer for around 48 hours.
Don’t Tighten the Lid All the Way
Avoid tightening the lid completely when the contents inside aren’t fully frozen. By doing so, you’ll leave some space for air that wants to get out.
You can tighten the lid all the way a few days later when the contents are frozen (you won’t get freezer burn).
Similarly, either loosen the lid or remove it entirely when thawing jars. This can help prevent the jar from breaking.
Cool the Jars Slowly
Thermal shock can easily break jars in the freezer, and that happens when there’s a sudden change in temperatures that’s just too much for the jar to handle. For instance, it could happen when you put piping hot sauce into the jar and then chuck that right into the freezer without letting it cool down first.
The best way to prevent thermal shock and keep the jars from breaking is to cool them as slowly as possible. There are a few ways to do that:
- Either fill the jar once the contents cool down or fill it up with hot contents and let it cool down to room temperature.
- Once both the jar and the contents cool down to room temperature, put it in the fridge for 24 hours or at least overnight before putting it in the freezer.
- Put the glass jar at the top of the chest freezer or in the freezer door. Make sure the lid is slightly loose and that you don’t put the jar at the back of the freezer at the start.
- Once the contents are completely frozen, tighten the lid more. You can then move the jar to the back of the freezer.
Thaw Jars Slowly
You also need to be careful when thawing your glass jars. Some tips you should keep in mind are:
- If you have enough time, put the jar in the freezer door or at the top of the freezer to let it thaw a bit. But if you don’t have too much time, you can just move the jar to the back of the fridge and twist the lid a little to slightly loosen it.
- Let the jar thaw by around 75% before moving it to the counter to let it finish thawing. Either loosen the lid more or just remove it entirely.
- Once the jar thaws up around 90%, pour the contents into a different container to warm them up.
- Make sure you never put the jar in the microwave or hot water for thawing. Even if the contents are thawed, your jar might not be at room temperature, so it’s better that you use a different dish.
Try to Avoid the Cooling Elements
All freezers have a cooling element — and to prevent the jar from breaking, you should avoid putting the jars beside, next to, or on top of the freezer’s cooling element.
For an upright or a side-by-side freezer, the cooling element is usually at the very back. In a chest freezer, it’s normally on the bottom.
Leave Some Space Between Jars
As mentioned earlier, both the contents and the jars contract and expand in the freezer. So when you cram jars beside each other, there’s no space for them to expand. Plus, frozen glass is highly susceptible to breakage.
Not to mention, if you store the jars close to one another, they’ll rattle whenever you open the door. Storing them very close can also affect the speed at which they freeze. Keep in mind that you don’t want the jars to freeze very quickly.
One way to leave some space is to put socks around the jars and let them act as buffers.
Is It Better to Freeze Food in Plastic or Glass?
There are numerous benefits of using glass. These include the following:
More Environmentally Friendly
Given its longevity and durability, glass is often preferred to plastic. With proper care, it can easily outlast plastic in the kitchen.
Similarly, while plastic can melt or get discolored, glass is a more long-lasting and durable solution, especially when it comes to storing food.
Plus, glass is completely recyclable, making it a more environmentally friendly option.
Healthier Than Plastic
In terms of safety in the kitchen and health benefits, glass is a much better option. Even BPA-free plastics tend to release toxic chemicals when heated, so heating, washing, and microwaving plastic containers can put your health at risk.
Plus, plastic containers tend to melt and warp, so you can’t put them in a dishwasher, either.
Meanwhile, glass can tolerate heat much better, and you can place it in the dishwasher, heat it in the oven, or even microwave it. It’s also non-porous, so it doesn’t release any microscopic particles or toxic chemicals.
Better for Storing Leftovers
Just like plastic containers give out chemicals when they’re heated, they do the same when they’re frozen. And for better food safety, it’s better if you choose glass.
Glass containers, like these from Pyrex (on Amazon), are fridge and freezer-safe and won’t break or release harsh chemicals when they’re frozen. Some are also leakproof and provide a tight seal to avoid spills and prevent the food from rotting.
These properties also make glass great for pickling and canning.