I'm assuming there was some minor siphoning during the canning process. Did you wash and dry the jars before storage? It's very important to be sure rings are removed and jars are clean before shelving.

Carol

I always rinse off my jars after they have cooled. Usually such thngs dissolve in the boiling water bath, unless there was some contamination leaking into the water from the jars. You can rinse and wipe off with a weak solution of water and a little bleach. I must assume that the lids were new and and are all concave with the button indented in the center, which indicates a vacuum inside.

I would just wipe it off with a bleach solution, as you suggested.
I used to have this problem frequently with my canned whole tomatoes (PC processed). While I don't think it's dangerous, it is certainly not desirable. Now, after my jars have rested overnight, I remove the rings and give each jar a "bath" in a bleach solution as mentioned above. Let the solution dry, date the lid and store in a cool, dry place. Since I have been doing this, no fuzzy mold!

Thanks to all for the info. I am continually amazed by the amount of good, usable advice and KNOWLEDGE on this site!! Thanks again.

Steve

I agree, wipe them off with a weak bleach solution and they should be fine.

I always take the rings off my jars before storage and wipe them well to present mold and because if I leave the rings on they seem to "cement" themselves to the jars or rust and I can't get 'em off!

good thing that's what the instructions say I should do. Plus, I reuse those rings several times during a canning season.

Annie