mold under lid of canning jar

kterlep(5/6)April 7, 2009

Yuck! I opened up several jars of tomato sauce (canned via Blue Book method). One of them had some black mildewy-looking mold (very fine, not furry looking) on the lid. What could have happened? Maybe the jar didn't seal well? All of the other jars smelled great, but I was afraid to smell that one (dumped it instead).

Still, a 1:40 failure rate isn't bad for a first-timer...

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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

Not bad ratio. ;) Imperfect seals can be caused by several things: chips or cracks in jar rim, sometimes so small you can't see them so a finger check helps, rubbing finger around the mouth of the jar.

Seals on the lids not pre-warmed (tho less of a problem with the new sealing materials), food or seasoning particles left on mouth of jar that didn't get wet wiped before putting the lid on, warped or bad ring bands, bands not applied to correct tightness so boil over during processing lodges food under the lid, tipping the jars after processing or lifting jars by tops while hot, etc.

It happens to all of us now and then. ;)


    Bookmark   April 7, 2009 at 11:01PM
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Shoot - I didn't check the jar. Oh well. live (hopefully despite botulisticsaucejar...) and learn!

Making room and emptying canning jars for new season...I have a LOT of pickles to eat in the next two months. :) Apparently I am the only one who likes dilly beans and pickled asparagus.


    Bookmark   April 7, 2009 at 11:58PM
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ksrogers(EasternMass Z6)

Smelling bad is only one way to tell, but keep in mind botulism does not have any odor or color differences. Lids get pulled in slightly when that small dimple in the center goes concave. Suggest that you make sure there are no chips on the sealing lips of the jars, the lids are new, clean and soaked in hot water before applying them. Tightening firmly is important too, but not overly tight to the point that its difficult to remove the rings.

    Bookmark   April 8, 2009 at 1:12AM
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Occasionally,I have found the same black substance on the underside of canned tomato products. It looked more like soot than mold, about 1/2 inch area, not raised. The contents were canned properly and smelled fine. I used it without a problem.
I assumed it was a chemical reaction of some sort.

    Bookmark   April 8, 2009 at 8:38AM
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Yes! it looked like soot! What is it???

    Bookmark   April 8, 2009 at 10:31AM
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See the link below to the Iowa university site. See if it might answer your question, as it is in the list of questions at the bottom of the article. If your seals are good, but you still see the black spots (it has happened to me too) it may.

Here is a link that might be useful: spots on inside of lid

    Bookmark   April 19, 2009 at 3:49PM
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ksrogers(EasternMass Z6)

Could be a bit of corrosion that comes off the metal lid. All you need is very slight scratch or two and the special coating is left unprotected for the metal lid and can get attacked by the acid in the tomatoes. I don't see gray, but a bit darker red around the rims of the lids where the glass and rubber seal meet.

    Bookmark   April 19, 2009 at 6:15PM
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cream_please(z5 PA)

Hi Kate,
By now you've most likely got an answer you're satisfied with however, I'd like to share my experience with you. Out of seventeen jars of homemade tomato sauce I found 4 that had black spots on the lids.
The first one was AFTER I'd ingested some of the sauce!!!
Long story, short: I talked to a county extension agent, and described the material exactly like you did: it was more like "soot" rather than "mold". (I carefully removed one of the spotted lids and took a toothpick to scrape some of the black deposit. It was dry and powdery, not wet, smelly or sticky.)The contents of the jars smelled clean and bright and the seal was tight with the proper popping sound when removed.

Here's a direct quote from the 2006 "Ball Complete Book of Home Preserving" by Kingry and Devine, P.425
"Problem...Black spots appear on the underside of metal lid.
Cause: Natural compounds in some foods cause brown or black deposits on the underside of the lid. This deposit is harmless and does not mean the food is unsafe to eat.
Prevention: None..."

I have been using my canned tomato sauce and it has been fine.


    Bookmark   April 20, 2009 at 8:47PM
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Cream, you and I both must have done that. I took the lid and the jar of tomatoes and went to my local Extension Service. After inspection my very helpful agent gave me the same information, that some natural compounds cause deposits under the lid.

I also learned that it's perfectly normal for canned garlic to turn pink or blue sometimes, and that my homecanned sweet corn turned an odd rusty color because it was too mature, but that I could have prevented some of the discoloration with some citric acid. Maybe, no promises from the extension agent, LOL.


    Bookmark   April 21, 2009 at 2:57PM
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Annie, The sugar in the corn, can cause it turn dark when pressure canned. I like to eat the SE's fresh but I only can it to use in soup. Frozen, it's OK. Too bad they don't grow corn like they did 50 years ago, like Golden Bantam. We grew acres of it for wholesale market. Stayed a nice yellow color when canned.

    Bookmark   April 21, 2009 at 4:45PM
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ksrogers(EasternMass Z6)

Ascorbic acid works better to keep corn from oxidizing. My corn relish also had a brownish color and I had not used the ascorbic that time. Golden Bantam and Legend yellow corn are still big seed sellers. I will be growing the Legend as well as a couple of other non hybrid types. Avoid the Sh2, SH, and SE types, they are just too sweet and are meant to retain sugar a week or more after picking, but are not as flavorful. You cant plant the hybrids near the regular types either as they all end up as stunted cow corn. I don't even care for the bicolor types either.

    Bookmark   April 21, 2009 at 5:42PM
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thanks everyone...

nobody got sick, so the funny black soot is likely not a killer. :)

    Bookmark   April 23, 2009 at 5:46PM
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