[Madame Cholet]

I opened a jar of black berry and apple and it has a tiny bit of mold on the to but it had a good seal any ideas? Mrs Bee

[surbie100]

Am not Mrs Bee but I would have thought it's any of too much air in the jar, jars not clean enough, the seal isn't as good as it should be or there isn't enough sugar in the jam. Though to be honest that is just a list of everything I could think of. Sorry it's mouldy.  I'd still eat it if it tastes nice.

[Madame Cholet]

Thanks Surbie it popped when I opened it.
Yes it tasted ok just a little on top I scraped it off, I think the whole lot would go molding if the sugar was too low.

[Mrs Bee]

Were you using recycled jar lids?
This can happen when reusing lids. I use recycled jars for my own personal use but always use new lids. they are only a few pence per lid and I think it is worth it.

Another reason could be that there was too much liquid in the jam or you didn't boil it down enough when you added the sugar. I simmer blackberries and strawberries down until the fruit is quite thick before adding the sugar.

Another thing I use is a sugar refractometre which shows me the sugar content of the jam. I cook the jam until I get a sugar content of 60 to 65% sugar.

Did you fill the jar to the very top? Was the jam boiling hot or did you let it cool slightly.

I fill to the very top, pop the lid on and immediately turn the jar upside down while the jam is still very hot. this just  helps to kill off anything else.

Another possibility is that the top of your lid might have been wet or damp.

Did you put one of those circles of waxed paper that you get in packets of cellophane jam lids on top of the jam.  I have found that they can trap bacteria in the jam.

What ratio of sugar did you use in the recipe?

[LotuSeed]

The same thing happened with a couple of jars of strawberry jam that I made this summer. All the lids were new and everything was sterilized before being processed in a boiling water bath for 10 minutes. The jars sealed and stayed that way, I only noticed the mold because I was organizing my root cellar.  I always make low-sugar jam and I think this might be why they went moldy. Strawberries have a high water content and I think that might have played a role as well and I don't think I cooked them down enough. (The thicker batch I made didn't have mold issues)  I believe sugar only acts most effectively as a preservative when it makes up 50% or more of the final product so, if your jam was low or no-sugar that might be why.
I chucked the contents of all the jars that had mold on them.

[Madame Cholet]

I guess it could be any of those apart from letting it cool and I don't use wax, I'l try turning them over.  I usually go for 50-50 sugar It was a tiny bit on top so it wasn't the sugar.

[snowdrops]

I only ever use waxed circles & plastic circle lids. I was amazed when I came on here that people buy new jars & lids for home use. I have had jam that lasts 5/6 years, it had shrunk a bit was ok to use in cooking.

[mumofstig]

I guess it could be any of those apart from letting it cool and I don't use wax, I'l try turning them over.  I usually go for 50-50 sugar It was a tiny bit on top so it wasn't the sugar.

The mould found in jam jars, only starts where there is air, so it only ever starts on the top - so don't discount low sugar levels.

[LotuSeed]

I'm wondering if my problem was actually just been a discoloration issue and not mold. Especially since I used the boiling water bath method to can them.  I don't use wax either, liquid or disc form.


Did you scrape off the foam before you put the jam into bottles?

How much headspace did you leave?

Did you add lemon juice to the jam mixture?

Snowdrops
I use new lids every time I can. The rings that screw the lids on can be reused over and over again. (I remove the bands before storing the jars and thusly have a huge surplus of rings just hanging around lol).
I also reuse jars, but only ones that I purchased specifically for canning. I never can anything in jars that have been bought from grocery stores that have product in them, mainly because it's not a recommended practice here.   (I think that's due to the size variations in commercially canned glass jars and the variability in glass thickness.)

[Mrs Bee]

I only ever use waxed circles & plastic circle lids. I was amazed when I came on here that people buy new jars & lids for home use. I have had jam that lasts 5/6 years, it had shrunk a bit was ok to use in cooking.

I always used to use waxed circles and reused jars for the home 4o years ago when I was young and fresh faced.  Where we stored the jars we had a mouse problem! and the little blighter got the  preserves.

I go by the WI information on preserve making these days and go with new lids for home preserves.

Making for sale legally is a whole different ball game.

MC I would say that as you sterilised the jars and lids well it sounds as if you needed to simmer the fruit longer to get rid of the water and there was too much air in the jar.

I had something like that with one batch of strawberry. Mould developed but only after  I  opened them. They had a sugar content of 50%. Since I cook to  a sugar content of 60%  Touch wood I have not had a problem like that since.

Some strawberries are more watery than others.

I always fill to the absolute top of the jars and then turn them upside down immediately. Any jam that does not fill a complete jar I store in the fridge and eat up first.

I also had a problem with mould around the outside of a couple of jars of chutney. I assumed that I had left a trace of chutney on the outside of jar before I put the lids on.

I removed all jars from that batch from my selling cupboard, opened and checked them They were fine inside but to be sure I recooked it and repotted the chutney and we ate them.

Now I wipe the outside of the top of the jars with a solution of Milton before I put the lids an and no more probs.

[LotuSeed]

Mrs Bee I've had mold form on the outside of jars before too. There was nothing wrong with the contents of the jar, the problem was that during processing a small amount of the contents leaked out and the residue stayed on the jar.  Now I wash the jars in warm soapy water 24 hours after taking them out of the canner.

[Mrs Bee]

Hi LotuSeed. Yep, I always wash the outside of the jars in soapy water too but I do it straight after potting as the warmth of the jars get them dry quicker.

However despite really careful washing I still get a couple of jars with a sticky patch on the main body of the jar and end up having to polish the jars before labelling.

[LotuSeed]

Hi LotuSeed. Yep, I always wash the outside of the jars in soapy water too but I do it straight after potting as the warmth of the jars get them dry quicker.

However despite really careful washing I still get a couple of jars with a sticky patch on the main body of the jar and end up having to polish the jars before labelling.

Applesauce gives me the most trouble in this area and I usually have to scrub the threads of the jar pretty aggressively to remove any seepage lol. 

[Mrs Bee]

It was tomato chutney that gave me the problem. Perhaps because tomatoes are watery.

I have found that wiping the tops and ridges of the jars with the Milton solution is doing the trick. Haven't had any problems since. Touchwood.

What is the time where you are. Are you up early or up late.

[LotuSeed]

It's early. I've been up since 3 something, but it's almost 6 am now.