A canning jar with a failed lid is something I’ll come across once in a blue moon. It’s a fairly rare occurrence and is always a rude surprise.
When I find a jar of home canned food in my pantry with a breached lid I dispose of the food carefully. Well out of the way of people or animals.
After the offending jar is emptied, it’s thoroughly washed and then closely examined for nicks around the rim or hairline cracks. A Mason jar must be near perfect for a lid to make a good strong seal.
With a faulty jar the vacuum inside the jar is eventually breached and allows spoilage to occur. Bacteria and yeast will begin to grow inside a jar causing fermentation and gas. Sometimes the force of the gas will blow a lid off and sometimes knock the lid to the side of a jar.
Slime and mold on top of any food product tells me that the 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 countertop 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 one trip lids are not simmered long enough problems can occur. The red rubber lining on the lid 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, many times the lid will not give a good 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 the jar of green beans above.
- Often the reason will remain unknown and it can be a guessing game.