There are certain rules in canning that when followed, food is safe to eat and preserved for a long time. However, sometimes the lids just don’t want to cooperate. You might find a jar with a bulging lid, or even one that completely became unsealed. This happens in commercially canned food as well, so don’t feel bad if it occurs to an occasional jar. In both cases the jar and it’s contents should be tossed, I am not referring to jars that you just processed, but ones that have been sitting on your shelf for some times. You cannot smell or taste the bad bacteria, so no sampling of the contents is allowed. I know it is hard to toss jars, but this reduces the chance of spreading bad bacteria that might be present. The jar and all of it’s contents are placed in a plastic bag and tied in a knot. Once the jar is in the garbage, sanitize any area of the kitchen the jar or contents came in contact with, and thoroughly wash your hands. While this doesn’t happen often (I had my first one yesterday in years) you should be prepared for how to handle it.
Sometimes you will discover black discoloration on the lid after opening. I know your first thought is mold, but take a deep breath. This is normal and occurs due to a chemical reaction. As long as it is more of a powder and not soft and fuzzy the contents are safe to eat.
Mistakes that might prevent seals not staying are easy to make. Make sure all jars are sanitized and that lids are following the newest guidelines before using. This means no more boiling, just place into hot water. Check jars for nicks before using. Wipe rims off with a wet rag before placing lids on. Use the proper sized headspace to prevent leakage. This leakage can leave a residue, preventing a good seal.
Something to keep in mind is the lids no longer need to be boiled. If you read the box you will see they only need to be dipped into hot water and then placed on the jar. Many suspect that since the change in procedure that those who use the old practice of simmering in water damaged the rubber seal which led to an increase in unsealed jars.
On a side note, there is a particular company who is advertising that it’s pressure cooker can be used in canning, however, when confronted has admitted that it has never properly been tested as a pressure canner, Only use a pressure canner to process food in.
Ultimately the goal is not to lose any of those beautiful jars that you made, but now you know what to do if it happens. Canning is such a great way to control the quality of what you are eating while limiting the added salt and sugar. Happy canning my friend!