Why A Canning Jar Lid Will Come Unsealed

This morning while going through my corner cupboard I found a jar of home canned green beans with a popped lid.
A canning jar lid failure is something I will come across once in a blue moon – maybe one jar every 4 years or so. It’s a fairly rare occurrence.
The other jars of green beans from the same batch are fine.

What happened is that the lid did not make a good, strong and permanent seal. The vacuum inside the jar was breached and allowed spoilage to occur.
Bacteria and yeast began to grow inside the jar causing fermentation and gas. The  force of the gas from the fermentation blew the lid off and knocked the lid to the side of the jar.
Slime and  mold on top of the beans tells me that this jar has been opened for a while.

Usually if there is a sealing failure with a jar I’ll catch it with my “lift test” after the jars cool from processing.
My lift test consists of me lifting a jar about 2″ above a table or counter top by the rim of the lid.

If the lid holds and doesn’t come loose the seal is good.
There are many reasons for a faulty seal on home canned foods.

  • Sometimes jars will not seal properly if the rim of the jar is not wiped perfectly clean before the lid and band are applied.
  • Also if the lids are not simmered long enough problems can occur. The red rubber lining on the lids must soften up a bit for a really strong seal. I simmer lids 3 -5 minutes.
  • If grease or some other material from the food product becomes forced under the lid while processing, often the lid will not give a good strong seal. This past summer I had 4 or 5 quart jars of ham & bean soup, from 2 different batches, that gave that kind of trouble. Grease had been forced between the lids and rim of the jars and prevented sealing.When I get food that doesn’t seal or pass the “lift test” I simply freeze it. It’s too much trouble and a waste of LP gas or wood to re-process it.
  • Canning jars that have not been kept hot enough before packing or suffer inadequate processing time will sometimes cause a lid failure. This is especially true when processing cold pack food.
  • Sometimes there is an unseen hairline crack in the jar or a nick on the rim. This is I believe what happened to this jar of green beans.
  • Often the reason will remain unknown. It can be a guessing game.

I did find a couple of nice things in the cupboard this morning: 2 quarts of grape juice and some raspberry jam.
I also found a surplus of apple sauce, canned pork, elderberry syrup and chicken stock.


Katherine Grossman

Katherine Grossman was born and raised in the greater Washington, D.C area. But for the last 30 years Mrs. Grossman has lived a life of deliberate self-reliance in rural western Pennsylvania. She loves to garden, knit mittens; makes a killer meatloaf and has been known to deliver triplet lambs with her eyes closed.