Freezing Glass Jars: The Plastic Free and Safe Way to Store Leftover Food

freezing glass jars - berries

Freezing food is an excellent way of ensuring your leftovers are safe to consume. What’s more, freezing glass jars full of food is a practical way to preserve food that might otherwise go to waste. It also minimises our consumption of single use plastics.

Pre cooked food, drinks and fresh produce can keep for months when they’re stored in the freezer. In the fridge they’re likely to only last a few days or a week at most. 

Plus, batch cooking your favourite recipes and freezing individual portions makes weekday meals super simple. That’s why frozen ready meals are so popular. But why not make your own with better ingredients, no nasties and no plastic?

Most ready meals come packaged in black plastic trays. But black plastic recycling is surprisingly difficult. In the same way, most of us freeze our leftovers and homemade meals in plastic tubs or disposable bags. 

But there is a better option!

Let’s take a look at how freezing in glass can help us on our way to using less plastic.

Are Glass Containers Better Than Plastic?

For decades, plastic boxes and bags have been our go to containers, and why shouldn’t they be? Plastic is durable, reusable, dishwasher safe and resistant to high and low temperatures. 

Glass is 100% recyclable but many types of plastic are also recyclable. Assuming that our plastic containers aren’t single use, are there any advantages to freezing in glass rather than plastic?

Yes! 

freezer with plastic

Glass is much cleaner than plastic. Its surface doesn’t absorb liquids and foods the way that plastic does. Plus, glass containers don’t develop bad odours or harvest bacteria. Nor do they leak potentially harmful chemicals into our favourite foods. 

Glass also holds up well to heat – that’s why you can put your glass containers directly into the oven or microwave. But it also stands up to cold temperatures too!

When you’re freezing glass jars, you don’t need to transfer your thawed food to a cooking dish or wash up an extra plate. There’s no need to wait for your leftovers to cool down before putting them into a glass container either. 

Let’s compare this to plastic. It’s now known that there are health risks involved in heating foods in certain types of plastic. 

Many plastics contain chemicals such as bisphenol-A, better known as BPA and phthalates. Both of these are known to contribute to health issues such as hormone disruption. Some scientists have even linked BPA to obesity and infertility. 

Even plastic containers marked as microwave safe can leach toxic chemicals when heated. This is even more of an issue if the surfaces are scratched or damaged.

We should also bear in mind recycling. Many types of plastic are technically recyclable. But not all recycling centres are equipped to process all kinds of plastic. Your plastic container may end up leaching chemicals in a landfill site even if you put it in the recycling bin.

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Does Glass Break in the Freezer?

Some of us know from experience that glass can break in the freezer. This only tends to happen when the containers are overfilled or stacked too closely. 

The trick is to leave plenty of space at the top of the jar. Liquids expand as they freeze, so when there isn’t enough room the pressure builds up and causes the glass to break. 

Approximately one to two inches of empty space at the top of the jar is ideal, depending on what you’re freezing. Liquids tend to need more expansion space than solids. So for soups, broths or drinks be sure to leave a good two inches.  

Another trick is to place the lid on without tightening completely. Wait until the contents are completely frozen, then tighten the lid. 

This is because tightening the lids creates extra pressure. Making it more likely that your homemade tomato soup will flood your freezer like the Red Sea.

freezing glass jars - supermarket jars

Can I Freeze Any Type of Glass?

Not all glass is made equal when it comes to freezing. So you need to make sure you’re freezing in glass which is designed to be frozen. 

Regular glass used to make tumblers or wine glasses isn’t strong enough to survive a trip to the freezer. But tempered glass is stronger and made to withstand more than regular glass.

Most canning jars, like the ones that jam and pasta sauces come in, are made from tempered glass. This makes them ideal for reusing and freezing food.

Straight sided jars or slightly conical shaped jars with wide openings are best. They help to reduce the pressure of expansion and reduce the risk of breakage. They’re also easier to fill. 

Of course, you can use jars with ‘shoulders’ (a rounded top) rather than straight or conical jars. But you’ll need more space in your freezer. For rounded jars, measure the one or two inch gap from the point where the jar begins to narrow.

freezing glass jars - pickles

How to Freeze and Defrost Food in Glass Jars

Freezing food in glass jars is easy, practical and helps us to reduce the food waste problem. Here’s how to do it:

Cook Your Favourite Recipe

Cook up a batch of your chosen food, ready for freezing. Soups, vegetable broths and sauces all freeze well. Dried chickpeas and beans are far too slow to cook on a daily basis. They’re ideal for cooking and freezing in batches too.

Portion it Up

When you’re ready to fill your jars, remember to divide the food into individual or family sized portions. This will speed up the thawing process and avoid food waste. 

pouring into jar

Let It Cool

You can transfer the food from pot to jar while it’s still hot. But freezing glass jars full of piping hot food is going to end in disaster. Don’t put them in the freezer until they’ve cooled completely. Leave the lid off during this stage. For hygiene, you can cover the open jars with a clean cloth. 

Clear a Space

Whilst the food is cooling, clear enough space in the freezer. Don’t try to stack the jars on top of one another or cram them into your freezer like sardines.

Let It Freeze

When the food has cooled to room temperature it’s ready to go in the freezer. Leave the lids loose until the contents have fully frozen.

And here’s how to defrost: 

Take It Slow

Defrosting foods in glass can take up to 24 hours depending on the amount of food in one jar.  So you’ll need a little advanced planning. It’s best to transfer your glass jars from the freezer to the fridge until the contents have mostly thawed. 

You can do this the night before and leave them in the fridge while you’re at work the next day. Then you can remove the jar and allow it to defrost completely at room temperature when you get home.

freezing glass jars - fruit preserve

Speed It Up

To speed up the process, you can put the frozen jars into a bowl of cool water then change the water every half an hour. 

Never…

Don’t put frozen glass jars directly into a heated oven, microwave or under hot water. This will almost certainly crack the glass.

Freezing Glass Jars – the Future of Freezing Foods

Reducing food waste, using less plastic and having fewer toxic chemicals in our diet are all benefits of freezing in glass. We can reduce plastic consumption whilst reducing food waste and potentially turning forgotten veg into tasty treats

Freezing glass jars and thawing them is a slower process than using plastic containers. But with a little practice and planning, it’s just as easy and could soon become second nature. 

To get started, you can buy eco friendly glass jars at many UK stores, but freezing glass jars doesn’t need to cost a penny. You might even have a few empty jam jars that are waiting to be thrown out.

Instead of sending your empty jars for recycling, why not reuse them for freezing leftover food? Free, eco-friendly and reducing food waste. What could be better?

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