Date: May 1989 (April 1995)
Source: University of Wisconsin
Failure of jellies or jam to set firmly is the most common problem faced by home jelly-makers. This can happen if you use the wrong proportions of fruit or fruit juice, pectin or sugar. Some fruits are too low in acid to form a firm gel unless you add lemon juice or some other acid fruit to them. Other fruits, such as most soft berries, are low in natural pectins; you will need to add either powdered or liquid pectin or a high-pectin juice to them to gel firmly.
The most common ingredient proportion problems happen when you intentionally reduce the amount of the sugar called for in jam and jelly recipes. Although the amount of sugar needed for some jellies may seem high, it is essential if you want good results. To make jams or jellies with reduced amounts of sugar, you need to use modified or low-methoxyl pectins: some examples of these are Sure-Jell Light, Mrs. Wages Light Home Jell, Slim Set Fruit Pectin and Pomona.
Tough jelly is usually the result of boiling it too long.
Cloudiness in jelly detracts from its appearance, but is a fairly minor problem, usually caused by leaving too much pulp in the fruit juice. If you squeeze a jelly bag to force out more juice, you will also force out pulp and get a more opaque jelly. But the yield of juice will be greater, so it is a trade-off to consider.
Grape jelly sometimes contains hard crystals. These are crystals of tartaric acid which is naturally present in grape juice. If you extract the grape juice and let it stand overnight in the refrigerator before making jelly, you will be able to strain out tartaric acid crystals that form.
Moldy jelly results from poor sealing. The old-fashioned method of sealing the top of jelly glasses with melted paraffin is no longer recommended because it often allows mold growth on top of the product. Pour hot jelly or jam into sterilized standard canning jars, leaving only one-fourth inch headspace. Cover immediately with a regular two-piece canning lid. Then, process the jam or jelly in a boiling water bath canner for 5 minutes. This will usually give you a good seal and prevent mold growth. If you store jams or jellies in the freezer, you can also avoid the risk of mold. Throw away any moldy jams or jellies. Toxins produced by many types of common molds can easily spread throughout the entire jar, making the jam or jelly unfit to eat.
Additional information on this topic is included in the Extension bulletin HE-172, "Jellies, Jams and Preserves," which is available at your county office of the NDSU Extension Service.
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