I won't reply in regards to the black spots, but I have found that if you add some fruit fresh will help prevent the darkness on the top of the corn.

I think we need a bit more information. What instructions (i.e. time and pressure) did you follow for processing corn and are we talking about plain corn or creamed corn?

What brand of lid did you use?

Also, I can't tell from the photo - are these raised spots or are these like corrosion through the enamel?

"Soot" refers to a fungus on the ears of corn. If you'd had that you would have seen it when picking. Would you have used such corn for canning?

Carol

I did a raw pack whole kernel corn, packing the corn in loosely (didn't notice anything on the corn like fungus) and covered with boiling water leaving headspace. Process at 11lbs pressure for 55 minutes. They were all pints done in Presto canner as per Presto manual instructions. Lids are standard bernardin (canada) pop lids. I didn't store them with rings on if that makes a difference? I think the spots were slightly raised but not raised like I think of mold to be, but enough that i could move it off the lid with my fingernail

Tanner, your processing time is correct.

The factory coating on that lid almost looks a little uneven to me, although it's hard to tell by a photo...While I haven't found those myself, and I admit I'd be concerned too, WSU says this -

WSU.edu:
What causes brown or black deposits to form on the underside of metal lids?
The underside of metal lids is protected by an enamel coating. If there are any imperfections in the enamel, e.g., tiny scratches or pinholes, natural compounds in food can react with the metal in the lid to form brown or black deposits. These deposits are harmless.

I did a raw pack whole kernel corn, packing the corn in loosely (didn't notice anything on the corn like fungus) and covered with boiling water leaving headspace. Process at 11lbs pressure for 55 minutes. They were all pints done in Presto canner as per Presto manual instructions. Lids are standard bernardin (canada) pop lids. I didn't store them with rings on if that makes a difference? I think the spots were slightly raised but not raised like I think of mold to be, but enough that i could move it off the lid with my fingernail

Your processing time is correct and I'm inclined to believe it's a lid issue as corroded areas (especially with longer processing times) are not that unusual.

I think this comes down to your comfort level. Since you processed for the appropriate time, if the seal was good (i.e. you can turn a jar upside down over a bucket and the seal holds) I don't see anything of concern.

Also, if you're adding the corn to a stew or soup and it's going to be cooked for at least an additional 10 minutes at a low boil, IF there were a problem with toxins, the heat would destroy them.

I've canned long enough that I've seen corrosion off-and-on with a lot of different products and I'm kind of ho-hum.

But we weren't standing there as you processed, and I give a lot of weight to personal comfort. If you find yourself holding your breath every time you open a jar to use it, then discard is probably the best option.

I can say with confidence it can't be soot or other fungus. Not processed for that duration at those temps. Such things simply don't develop after the fact.

Carol

I had a spot like that on one of my jars too this year. The first thing I thought of was that mold had developed in the applesauce, but the vacuum was still good and I can process applesauce in my sleep, and I know I did it correctly. I also chalked it up to some sort of chemical reaction in an improperly manufactured lid. Ate the stuff and lived to tell about it. ;-) I have since reordered my usual lids from Lehmans, and tell ya.........the 'high priced' lids at the market don't match up with the quality I get when I buy in bulk.