When it comes to food preservation, freezing is one of the most effective methods to maintain freshness and extend shelf life. While plastic containers and zip-loc bags are commonly used for freezing, glass jars offer a safer and more eco-friendly alternative. Freezing food in glass jars not only helps reduce plastic waste but also allows for better visibility and eliminates concerns about chemicals leaching into the food.

Here are six tips to safely freeze food in glass.

1. Choose the right glass containers

Ideally we’d freeze everything in pyrex containers like these, but that could get expensive! Mason jars and canning jars are not as tough as pyrex but are designed to withstand temperature changes so they are probably the second best choice. It’s also possible to use recycled jars, but you must only use ones with a wide opening. The opening needs to be as wide as the body of the jar.

2. Select foods that freeze well

Not all foods are suitable for freezing in glass jars. Fruit and vegetables that have a high water content, like cucumber and melon, will be damaged during the freezing process as the water expands. This will leave you with a mushy mess once they are defrosted. The best foods to freeze are either low in water content, like broccoli, or meals that are already very mushy and liquid, like soups, stews and sauces.

3. Leave space for the food to expand

When filling the jars with food, leave enough headspace to allow for expansion during freezing. As a general guideline, leave about 1 inch of headspace for liquids and half an inch for solid foods. This extra space will prevent the jars from cracking or breaking as the contents freeze and expand. This is why it’s important to use widemouth jars, so that it’s easy to judge the headspace that you need.

4. Cool the food

It’s crucial to cool the food before filling the glass jars. Rapid changes in temperature can cause thermal shock and increase the risk of glass breakage. If you transfer leftovers after you’ve eaten, they are usually close to room temperature. After a meal you can safely leave food out to cool for up to an hour before transferring it to glass containers.

Once you’ve transferred the food to the glass containers, put them in the fridge for 12 hours first so the glass chills a little before going into freezing temperatures.

5. Label and date

To keep track of the contents and their storage time, take a sharpie and label each glass jar with the name of the food and the date of freezing. This simple step will help you identify the items easily and ensure you use them within a few months. The sharpie label will wash off in the dishwasher ready for next time.

6. Allow time for thawing

Keep in mind that glass jars take longer to thaw than other containers. Leave sufficient time for your food to defrost by transferring the jar from the freezer to the fridge a day or two before you plan to use it. This gradual thawing process helps maintain the quality of the food and reduces the risk of glass breakage.

Do not transfer a frozen jar directly from the freezer to a hot water bath or microwave. If you don’t have time to thaw a meal in the fridge, place the jar in a bowl of cold water.

If you follow these tips, you’ll be able to enjoy the convenience of freezer meals while reducing plastic waste. Happy freezing!