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The science of jams and jellies

By Jennifer Bridge

 Each year one of the first signs I see of canning season is request for information on making jelly, jam, preserves or conserves. The cooperative extension service is the reliable source for information on home food preservation. Research is routinely conducted and adapted based on chemical changes and evolution of bacteria as they seem to adapt to their changing environment quicker than humans. Please be aware of sites that tout quicker, easier ways and new methods to bypass traditional pressure canning. If in doubt please call me and I will provide evidenced based research on whether or not the information is valid.

 The fruits of summer are ripening fast, and it’s time to make some jams and jellies. Besides the fresh fruit, other ingredients are needed to form the perfect jelly, namely pectin, sugar, acid, and liquid, along with the application of heat. Knowing the science behind jams and jellies can help you have the taste of summer all year round.

 Fruit pectin is a starch found in fruits. When sugar is added, the natural pectin in fruit or commercial pectin forms insoluble fibers. An acid, such as lemon juice or citric acid, helps the process. These fibers create a honeycomb-like form that traps the fruit juice or other liquid, much like a sponge absorbs water. When the ingredients are heated, a gel forms. Recipes without added pectin use the natural pectin in fruit to form a gel. Tart apples, sour blackberries, cranberries, currants, gooseberries, Concord grapes, soft plums, and quinces work well in recipes without added pectin. Other fruits, such as apricots, blueberries, cherries, peaches, pineapple, rhubarb, and strawberries are low in pectin.

 There are two types of commercial pectin — liquid and dry. Check the use-by date to make sure your pectin is fresh. Powdered and liquid pectin are not interchangeable. There are also low-methoxyl pectins that allow you to use less sugar, but the result will not be quite as thick or glossy. The acidity level is also important to jelling. The gel will not set if there is too little acid. Too much acid will cause the gel to lose liquid or weep. For fruits low in acid, add lemon juice or another acid source as instructed in your recipe. Sugar is needed for the gel to form. It also acts as a preserving agent and contributes flavor. Do not attempt to reduce the amount of sugar in regular jam and jelly recipes as a syrupy gel will form.

 Other factors might affect your jelly. Too high of a temperature or cooking for too long can destroy pectin, resulting in a poor gel. Doubling the recipe changes the length of time needed for boiling and can result in a soft gel. Commercial pectin can be used with any fruit, even those high in pectin. Too much pectin will give the jelly a tough, rubbery consistency, making it difficult to spread. Follow the recipe guide that comes with the pectin to help eliminate this problem.

 For more information, check with your local Extension office for the publications The Science of Jams and Jelly Making or Home Canning Jams, Jellies, and Other Soft Spreads for more information.

Source: Sandra Bastin, Extension professor

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