Hi Linda,

I wonder if the store-bought has less sugar?

Hmm....makes sense...but I would think it would have more sugar and less fruit.
Hmm again....maybe that's why the orioles don't stay around.....

I don't think that it's the sugar content. We buy low sugar jam or the no sugar added fruit spreads, keep them at room temp and they don't mold during the time it takes to get through the jam. On the other hand my home made jam has to be kept in the fridge or it molds after it's opened for a week or so.

Perhaps the grape jelly had lots of time to pick up mold spores but them getting active was slowed down by refrigeration so when it was left at room temp they got going quickly?

For what it's worth, here's what they say at the National Center for Home Food Preservation on the subject....

-Grainlady

Opened home-canned jams and jellies should be kept in the refrigerator at 40-degrees F or lower. "Regular" - or pectin-added, full-sugar - cooked jams and jellies are best stored for 1 month in the refrigerator after opening. They may last longer depending on the specific product and how it is used. The expected shelf life will be shortened by keeping the container frequently open and/or out at room temperature for long periods of time during use. At each use, you can spoon out the quantity of jam or jelly that you may require into a bowl, and replace the jar in the refrigerator quickly - this would ensure minimum exposure to sources of microbial contamination during use. Do examine the container regularly during storage for any signs of spoilage like molds, yeasts and off odors (including a fermented, "yeasty," or "alcohol" odor), once it is opened. Discard the entire contents of the container if these are detected.

Lower-sugar or no-sugar-added spreads may have a shorter refrigerated shelf life than those made with the traditional amounts of sugar. Natural flavor changes in the fruit base are more noticeable without the sugar to mask them; for example, some lower-sugar spreads may taste more tart or acidic over time. Light-colored spreads may also darken more quickly with less added sugar.

Freezer jams also have to be stored in the refrigerator after thawing and will only retain good quality for 3 to 4 weeks after opening. They are subject to more syneresis ("weeping" or separation of liquid from the gel) than cooked jams and jellies.

Note: For safe eating practices, store your opened jar of jam or jelly in the refrigerator until consumed, and examine it frequently for signs of spoilage (like mold or yeast growth, or off-odors, including "fermented," "alcohol" or "yeasty" odors). Discard the product immediately if any signs of spoilage are detected.

The way you grow a wild yeast starter, is to use mashed grapes, left at room temperature (little more complicated than that--but the grapes are the key). It works beautifully--I can vouch for that from personal experience. If the grapes attract, catch and nourish yeast spores, stands to reason that perhaps mold would be similarly attracted to the product.

I second the advice of storing any jams and jellies in the fridge. I always do and in 39 years of running a household have never had any jams or jellies mold--whether they were store-bought or homemade.

Could it be the time of year? Maybe there's higher mold in your area at this time. Just a wild, and probably wrong guess.

Sally

FYI... The silvery "haze" on grapes are naturally-occurring yeast and that's why they are used for making a natural leavening (aka starter) and contribute the yeast to help build a nice colony of them in the starter. The sugars (carbohydrates) in the grape juice also feed the yeast along with the carbohydrates in the flour.

The silvery haze of yeast can also be found on cabbage on the inner leaves, which can be used to make a natural leavening. Even things like peach tree leaves, hops, and beer were used to contribute the yeast for starters and homemade baking yeast made before WWII when fresh and dried yeast products were introduced. The outside of whole grains are also teaming with naturally-occurring yeast, which is why whole grain flour is often a good choice for making a starter.

If you do a lot of baking with yeast or make naturally-leavened breads, your kitchen is full of yeast spores. Occasionally, big bakeries have to do a thorough cleaning to eliminate yeast spores because they can affect the baked goods, especially if they are making naturally-leavened breads AND ones made with baker's yeast.

-Grainlady