Glass storage containers are versatile, durable, and sustainable. But can you put glass in the freezer without creating a mess? And, if so, is all glass freezer-safe?
Can You Put Glass in the Freezer?
Yes. In fact, glass is one of the best materials to use when storing leftovers or other food in the freezer.
With that said, glass is not 100% freezer-safe. There’s always a small chance that glass will crack or shatter when exposed to freezing temperatures.
But there are many steps you can take to prevent this from happening in your own kitchen!
What Causes Frozen Glass to Break?
Thermal Shock
Thermal shock can occur when something is exposed to drastically different temperatures. It affects many materials, including glass.
Thermal shock most often occurs when something is moved from the fridge/freezer to the stove or vice-versa. The most common effects of thermal shock include cracking and shattering.
Avoiding thermal shock is important to not only save your glass containers but also because shattering glass can be extremely dangerous.
Expanding Contents
Freezing is a chemical process. While the most obvious physical effect of freezing is that it solidifies liquids, it can also cause substances to expand.
This expansion isn’t an issue when the liquid has room to breathe. But it can be a big issue when freezing glass containers filled to the brim with water, sauce, soup, or another liquid-based food.
Air Bubbles
Air also expands when exposed to sub-freezing temperatures.
Some types of glass (most notably, non-tempered glass) feature tiny, sometimes invisible air bubbles throughout. Placing this glass in a freezer could result in the air inside those bubbles expanding and causing the glass to break.
How to Prevent Glass Breaking in the Freezer
Check the Label
Tupperware, jars, cups, and dinnerware that are safe to put in the freezer are generally labeled as such. This label can be found on the bottom of the item and will list whether the glass can also be placed in the microwave, oven, or dishwasher.
Not all glass objects feature care instructions. For example, glass items that are designed to be decorative rarely have these labels.
If a piece of glass is unlabeled as safe or unsafe to put in the freezer, it’s always best to err on the side of caution.
Leave Extra Room
You can account for the expanding contents of glass containers by leaving a bit of extra room at the top. This is typically called headspace.
Not much headspace is needed to prevent the glass from cracking or shattering. Leaving ¾ -inch of empty headspace will suffice in most cases.
Use Wide Containers
Tall and narrow containers can trap expanding contents in the bottom. This can result in the glass shattering regardless of how much headspace you have left inside.
Wide glass containers are much less likely to break due to expansion. Plus, you won’t need to worry about food storage containers falling over and breaking in the freezer.
Wait to Seal the Lid
Since much of the risk associated with freezing glass has to do with the contents expanding, waiting to seal your food storage containers can help prevent cracks.
The best strategy is to let your glass containers and the food inside reach freezing with the lid unsealed. This allows excess air to escape as everything expands.
Once the contents are frozen, it’s perfectly safe to seal the lid and store it as usual.
Note that traditional metal jar lids won’t always create an airtight seal in the freezer. Specialty lids are available for this specific purpose.
Final Thoughts
If your household frequently relies on prepped meals or leftovers, investing in a set of high-quality, freezer-safe Tupperware is definitely worth your while!
Glass Tupperware is not the only thing that can be safely put in the freezer. Many cups, jars, and even glass dinnerware can also be frozen. Just be sure to check the items’ care instructions before freezing.
With a few simple steps and the right glass containers, freezing is the most convenient way to keep food fresh for as long as possible.