If you're speaking of a full-sugar jam (i.e. "regular" jam) even open-kettle canned it's safe to eat unless there are signs of mold. Then it has to be discarded.

This is not an invitation to open-kettle can. Full-sugar jams and jellies are the only exception.

However, the shelf life is reduced and the likelihood of mold increases. If you want to process, I suppose you could. Most foods have a 24-hour window for this sort of thing, but again, jams are an exception.

You would need to remove the jam from the jars, bring back to the boil, have clean hot jars, prepped rings and lids and follow the regular boiling water bath process from scratch. I would check very carefully that there isn't even a hint of mold before mixing those individual jars of jam into a single batch.

Carol

Agree with Carol.

If you want a longer life for it once opened, you can add some acid blend to it, and stir it in. My jams are mostly sugarless and because I add Splenda and extra acid, they don't get moldy after opening. The blend consists of 33% each of citric, malic, and tartaric acids.

I did use a low-sugar pectin (I used maybe a 1/4 cup of sugar per cup of jam), would that make a difference? Also, if I did try to put sealed jam jars in a hot water bath, would that work?

If it's low-sugar it's even more important to re-process because the lower sugar level greatly reduces longevity and increases the likelihood of mold formation.

In fact, since it's now been several months at room temp some may have molded or fermented already.

No, you can't put the previously sealed jars in a boiling water bath. First, because the jars aren't heated there's a much higher risk of breakage. Secondly, you need to bring that jam back to the boil to kill off any incipient organisms that might have formed in the interval since the jam was first shelved. If you wish, this would also be an appropriate time to add acid as Ken suggested.

There is no simple no-pain way to correct this, I'm sorry to say. It takes time and fresh lids, so there's also an added expense. Believe me, I know re-processing is no fun, but there just aren't shortcuts.

Carol

If you don't see mold inside the jars, to extend their life a bit, you can place all the jars in the fridge, but as mentioned, mold may not be the only issue, but with the natural acid in the fruits, the risks beyond mold are usually miminal. For jams, as mentioned, its always necessary to reheat the jam to boiling, then fill clean jars and to process in a boiling water bath, with about 2 inches of water covering the jars, and of course with a cover on the canner. In the future, you may want to try the Pomona pectin as it has a better texture than the low/no sugar pectin, which tends to weap a bit. Pomona is so stable it has no expiration date, and can even gel water!

perhaps I misspoke: I did use Pomona's pectin, but I did not use the maximum amount of sugar in the recipe (the range the pectin directions give are between 3/4 and 2 cups and I think I used 1 cup or a little more). Would I still have mold problems with pomona's pectin? Also, if I took out all the jam, reboiled it and then recanned it with new lids in a boiling water bath, would the quality of the jam be affected very much? Thanks for your help!

Pomona Pectin is not a mold preventative. It makes no difference which pectin you used. A full measure of sugar and the natural acidity of the fruit will help to prevent the growth of molds, but in your case the level of sugar is quite low.

Jams and jellies are not "high-risk" regardless of how they're prepared because the fruit is acid and the sugar aids preservation. But jams and jellies with low levels of sugar are far more prone to spoilage, whether it's mold, fermentation or just a general oxidation and degradation of flavor and quality.

The options are to refrigerate, as Ken suggested. But since it's already sat at room temp unprocessed for some time, it's potentially going to have a shorter refrigerated life than a processed product just opened and refrigerated. If your family eats a fair amount of jam and it's not a very big batch, then consuming it quickly and leaving it unprocessed may be a suitable option. There isn't a full vacuum, but if you used sterile jars and hot sterile lids, there is a weaker seal, and that does help somewhat.

Re-cooking generally does affect the quality of the jam, but if you just bring the product to a good boil and don't overdo it before jarring, the effect should be minimal. The boiling water bath isn't going to cook the jam any further. It's a different sort of heat process.

Carol

As mentioned numerous times in many posts, adding extra acid to a jam will reduce the issue of mold. Actually, Pomona does NOT need ANY sugar to set up. it uses the calcium that is included in the box. Because I make mine with Splenda and a little honey, my jams would be suseptable to mold. If I increase the acid by adding the acid blend, it will raise the acidity level to a point that prevents mold from forming.

I agree with Carol, the best solution might be to do nothing, I wouldn't reprocess unless I had a jar ferment or mold. I make low sugar jams and spreads regularly without any commercial pectin at all. I find that as long as they are sealed, they keep well, I do have a quicker deterioration of quality after they are opened.

And, of course, if it's moldy or tastes spoiled, toss it out.

Annie