Date: May 1989 (Revised April 1995)
Source: University of Minnesota
Some of the most common problems with jams and jellies are softness, weeping, fermentation, darkening, clouding, mold and crystal formation.
If jelly is too soft, there may be incorrect proportions of sugar, acid and juice. Making too large a batch or undercooking may also be a cause.
Another problem is jelly that weeps. If this happens there may be too much acid in the fruit or too much acid added in the form of lemon juice. Also, the storage place may have been too warm or the temperature changed too much during storage.
Fermentation is another problem. This may occur because of too little sugar or improper sealing. The boiling water bath process helps to get an adequate seal and prevent fermentation.
Sometimes jellies and jams darken at the top of the container. There are two main reasons: Either the storage place was too warm--or a faulty seal has allowed air to leak in. Red fruits such as strawberries and raspberries are especially prone to fading.
If your jelly is cloudy, it may be for one of the following reasons: first, you may have poured the jelly mixture into the jars too slowly allowing bubbles to form. Or, you may have allowed the jelly mixture to stand before it was poured. Other reasons are that your juice may have had too much pulp because of improper straining, or your jelly set too fast, probably because the fruit was not ripe enough.
Mold growth may occur on jam and jelly products when there is an imperfect seal or too much air space between the jar lid and jellied product.
The prevention of mold growth on jams and jellies is important for economic as well as food safety reasons. We used to think molds on jams and jellies were harmless and should be scraped off before using the rest of the product. New information indicates that molds may be harmful and shouldn't be eaten. If mold does develop, throw away the entire contents of the jar.
The best way to avoid problems with mold growth on jam and jelly products is to pour the hot jam into hot, pre-sterilized half pint or pint size canning jars. Pour to within a fourth of an inch of the top of the jar. Seal with pre-treated two-piece lids and process in water bath for the recommended time.
A final problem is crystals in jelly. This may be caused by too much sugar or not cooking the mixture long enough for the sugar to dissolve. Another cause may be cooking the jelly too long or too slowly, and ending up with too much evaporation of liquid. Once the jelly is made, allowing it to stand uncovered may also result in evaporation of liquid and the formation of crystals on top of the jelly.
For future reference, you may want to obtain a copy of Extension bulletin HE-172, "Jams, Jellies and Preserves," which is available at your county office of the NDSU Extension Service.
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