Most canning jars are freezer-safe, but the way you fill and seal them matters more than the jar itself
Standard canning jars — Mason jars, Ball jars, and Kerr jars in quart and pint sizes — are made from tempered glass designed to handle temperature swings. You can freeze food in them. The real risk is not the glass breaking from cold, but from pressure inside the jar as liquid expands when it freezes. A jar that is too full, sealed too tightly, or filled with a liquid that expands more than others can crack or shatter in the freezer.
The safest approach is to leave headspace (empty space at the top), avoid sealing the lid tightly before freezing, and choose foods that freeze well in jars. Jams, sauces, and broths freeze better in jars than foods with high water content, which expand more aggressively.
Key Takeaways
- Canning jars made from tempered glass can freeze, but you must leave at least one inch of headspace to allow for expansion.
- Do not screw the lid on tightly before freezing; leave it loose or use a plastic freezer lid so pressure does not build inside the jar.
- Liquids and foods with high water content expand more when frozen, so they carry higher risk of jar breakage than thick sauces or jams.
- Thaw jars in the refrigerator or at room temperature rather than in direct heat to avoid thermal shock that can crack the glass.
Why jars crack in the freezer
Glass itself does not break from cold. Tempered canning glass is made to withstand temperature changes. The problem is what happens inside the jar. When liquid freezes, it expands — water expands about 9 percent. If a jar is completely full and sealed tight, that expanding ice has nowhere to go. Pressure builds until the glass gives way, usually with a crack along the side or bottom.
The risk is highest with foods that are mostly water: broths, soups, fruit juices, and pickles. Thicker foods like jams, nut butters, and tomato sauce expand less and are safer to freeze in jars. Even with thicker foods, headspace is still necessary because some expansion always happens.
How to freeze food safely in canning jars
Leave at least one inch of empty space between the top of the food and the rim of the jar. For liquids and soups, one and a half inches is better. This headspace gives the contents room to expand without building pressure against the lid.
Do not screw the metal lid down tight before freezing. Either leave the lid loose, use a plastic freezer lid (which is not airtight), or skip the lid entirely and cover the jar with plastic wrap. Once the food is frozen solid, you can tighten the lid if you want to, but it is not necessary. The frozen food will not spoil.
Wide-mouth jars are easier to fill and empty than narrow-mouth jars, and they are slightly safer because the wider opening reduces the chance of ice pushing against the lid with concentrated force. Both styles work, but wide-mouth is the better choice if you freeze jars regularly.
Which foods freeze well in jars and which do not
Jams, jellies, and fruit preserves freeze reliably in canning jars because they are thick and do not expand much. Sauces — tomato sauce, pesto, salsa — also freeze well. Broths and stocks freeze in jars if you follow the headspace rule, though they are more prone to cracking than thicker foods.
Avoid freezing foods with very high water content, such as raw fruit juice, clear broths made from just water and bones, or pickled vegetables in brine. These expand aggressively and are harder to manage in a sealed jar. If you want to freeze them, use plastic containers instead, or use jars with extra headspace and leave the lid completely off until thawed.
Soups with chunks of vegetables and meat freeze in jars better than clear broths because the solid matter takes up space and reduces the proportion of liquid that will expand. Cream-based soups are riskier because cream can separate when frozen and thawed.
Thawing frozen jars safely
Thaw jars in the refrigerator overnight or at room temperature on the counter. Do not run hot water over a frozen jar or place it directly on a heat source. The sudden temperature change can cause thermal shock — the outer glass warms and contracts while the inside is still cold, and the stress can crack the jar.
If you need to thaw quickly, place the jar in a bowl of cool water and change the water every 30 minutes. This is slower than hot water but much safer. Once the jar reaches room temperature, you can transfer the contents to a pot and heat it on the stove.
Comparing jar types for freezer use
| Jar Type | Freezer Safe | Best For | Headspace Needed |
|---|---|---|---|
| Wide-mouth pint or quart | Yes | Jams, sauces, thick foods | 1 inch |
| Narrow-mouth pint or quart | Yes | Jams, sauces, thick foods | 1 inch |
| Half-pint jars | Yes | Small portions of jam or sauce | 1 inch |
| Plastic freezer containers | Yes | Liquids, soups, high-water foods | 1 inch |
When to use plastic containers instead of jars
If you freeze a lot of broths, soups, or other liquids, plastic freezer containers are a better choice than glass jars. Plastic is flexible and expands with the contents, so there is no risk of cracking. Plastic containers are also lighter and take up less space in the freezer.
The trade-off is that plastic does not last as long as glass. After a few years of freezing and thawing, plastic containers can become brittle and crack. Glass jars last indefinitely. If you freeze occasionally and stick to thicker foods, jars are fine. If you freeze regularly and work with a lot of liquids, plastic is the practical choice.
Frequently Asked Questions
Can I freeze food in canning jars with the metal lid screwed on tight?
No. Screwing the lid on tight before freezing traps pressure inside as the food expands, which can crack the jar. Leave the lid loose, use a plastic freezer lid, or leave it off until the food is frozen solid. Once frozen, you can tighten the lid if you want to store it that way.
What happens if a jar cracks in the freezer?
The food inside will still be safe to eat if the crack happened during freezing and the jar stayed cold. Thaw it in the refrigerator and transfer the contents to a new container. Do not use the cracked jar again for freezing because the weak spot will fail again. You can use it for room-temperature storage or canning if the crack is small.
How long can I keep food frozen in canning jars?
Frozen food in jars lasts as long as frozen food in any container — typically 3 to 6 months for best quality, though it remains safe longer. Freezer burn and flavor loss happen over time, not spoilage. Label the jar with the contents and date so you know what you have.
Are vintage or antique canning jars safe to freeze in?
Older jars may not be tempered glass and are more likely to crack in the freezer. If you have jars from before the 1950s, test one with a small amount of water first. Modern canning jars from Ball, Mason, and Kerr are all tempered and safe. When in doubt, use a plastic container instead.
Can I freeze jars that still have the original canning seal on them?
Yes, if the seal is intact and the jar was properly canned. The seal will hold through freezing as long as you follow the headspace rule. However, do not rely on the seal to keep the food fresh — freezing preserves food on its own, and the seal is not necessary for frozen storage.