Canning Jars Not Sealing: Why It Happens and What to Do

Is it really unsealed?

Give the jars their full cooling time before you judge. The USDA says to cool them for 12 to 24 hours, then take off the bands and test each lid.

• Press the middle. If it springs up when you let go, it's unsealed.
• Tap it with the bottom of a teaspoon. A sealed jar rings. A dull sound means no seal, or food touching the underside of the lid.
• Look across it at eye level. It should curve down slightly.

Our guide to using a pressure canner has the whole sequence.

Don't press a warm lid or tighten a hot band. The USDA says tightening may cut through the gasket and cause the seal to fail.

What are the likely causes?

• Rim problem: a nick, crack or dip in the sealing edge (USDA, Penn State, Presto).
• Food on the rim: residue, seeds or grease between lid and jar (Penn State, Presto).
• Lid problem: reused, dented or scratched, or gaps in the sealing compound (USDA, Penn State).
• Old lid: the USDA says gaskets in unused lids work for at least 5 years from manufacture, and older ones may fail.
• Band too tight: air can't escape, and lids may buckle (Penn State).
• Band too loose: liquid may escape, or the vacuum is weak (USDA, Penn State).
• Wrong headspace (the gap at the top of the jar): too much or too little for that food. Your tested recipe gives the amount (Penn State).
• Rushed cooling or swinging pressure: liquid pushed out of the jars (USDA, Penn State).
• Jars turned upside down while they cool and seal (Presto).
• Lid brand: Penn State reports that off-brand lids may fail more often, based on stories, and that fake lids are sold as major brands. It names no brand.
• Recipe or timing: not following exact recipes and timetables (Presto).

What do you do with the jar?

1. Note the time

   The USDA and the National Center both work with a 24-hour window. Presto counts it from when the canner showed DONE. Do not taste the food.

2. Ask if the recipe was a tested one

   If the first try did not use a tested recipe, the National Center says all the jars, sealed or unsealed, may be unsafe and should be thrown out. Nebraska Extension words this differently. It allows re-canning within 2 hours where safe methods weren't followed. We report both and don't settle it. If this is you, ask your extension office (free local food-safety advice from your state's university).

3. Choose one of three options

   If the recipe was tested and the batch was processed correctly, pick from the list below.

4. If you reprocess, start the jar over

   The USDA says to take off the lid, check the rim for tiny nicks, change the jar if needed, add a new lid and reprocess for the same time. The National Center and Presto say more. Reheat the food, pack it into a clean hot jar and use a tested hot-pack method.

5. Label it

   Penn State suggests labeling re-canned jars and using them first, since they'll be softer and less nutritious.

Your three options:

• Reprocess. The USDA allows it in that same window. The National Center says it's not recommended for quality reasons. With no tested hot-pack recipe, the food may not be safely reprocessed.
• Freeze. The USDA, the National Center and Nebraska Extension allow it, with extra room left at the top for expansion. The USDA guide gives the amount.
• Refrigerate. The USDA says several days for a single jar. Presto and Penn State say 3 days. The National Center says within one week. We report the windows as they stand and don't pick one.

If a day has already passed since the end of the process, Presto's manual is firm. If the seal is faulty, the food is no longer safe and should be thrown out at once. The National Center's page on spoiled canned food says how to throw out a suspect jar. It's worth reading before you start, since it treats sealed and unsealed jars differently.

What if the whole batch failed?

When many jars fail, look at what they share. Maybe a box of lids, how tight the bands were, how the canner cooled, or an interrupted process. Read your canner's manual again.

If the machine stopped or the power went out, the question changes, because the process may not have finished. See what to do after a power cut. For a Presto Precise, see what its error codes mean.

If your recipe might be the cause, the tested recipes page shows where to look.

How do you prevent it next time?

• Run a finger around each rim before you fill. Penn State says to choose jars with no nicks, cracks or dips.
• Use a new flat lid each time, and look it over. Penn State says the sealing compound is only reliable for one seal.
• Wipe the rim with a damp paper towel. Then tighten the band only until your fingertips say it's snug, as Penn State describes.
• Follow your lid maker's directions on preparing lids, and let the canner cool by itself.

If you traced the problem to old lids or chipped jars, replacing them is an easy fix. Our jars and lids page explains what to buy and how much to keep on hand.