It’s a question every jam and jelly maker asks: why do some batches come out as a delightful spread that smears nicely on toast, while others are a syrup better suited for pouring over pancakes? Jams and jellies contain so few ingredients: fruit or fruit juice, sugar, and sometimes an acid and pectin. As with more complex recipes, success depends on respecting chemical ratios and reactions.
Fruit or juice is the basis of jams and jellies, of course, yet its obvious role is not its only one. Besides flavor and volume, fruit contributes two other essential ingredients: pectin and acids. Although pectin and acids are the smallest ingredients in terms of size, they form the glue that holds the sweetened fruit mixture together.
Pectin is a complex carbohydrate, or starch. It occurs mostly in the rind and core of the fruit, where it adds support to cell walls. Boiling the fruit when you’re making jam causes the pectin to be extracted. Overcooking, however, can result in too much breakdown.
Like other starches, pectin molecules include many branchlike side chains of atoms. In pectin, the chemical makeup gives these chains a negative charge. Normally, these like charges would repel each other. The fruit’s acid, however, plays a critical role. It alters the chemical environment to neutralize the charge, which allows the pectin chains to join together. The framework created by these pectin bonds traps the fruit molecules, resulting in that pleasingly thick consistency. Science calls the process gelatinization (juh-LA-tun-uh-ZAY-shun).
The strength of the bonds depends on the amount and proportion of pectin and acid, which vary among different fruits. Tangerines, for example, are high in pectin and low in acid. Strawberries are just the opposite. Pears are both low-acid and low-pectin. Pectin and acid levels reach their height in mature fruits and drop as the fruit ripens.
In some fruits, the level and ratio of acid and pectin are conveniently suited for gelling. Most recipes, however, boost the process with either additional acid, often in the form of lemon juice, or powdered pectin, commercially prepared from fruit peels. Sometimes both are added. Blending fruits is another way to increase and balance these ingredients. Some popular combinations, such as blueberry-lemon and pineapple-orange, may have developed from this need.
Sweetening the Deal
Like fruit, sugar adds more than sweetness and substance. Sugar is hygroscopic (hy-gruh-SKAH-pik)—it attracts water. This action combines with the work of acid to promote gelling. By drawing water molecules into its own structure, sugar encourages pectin molecules to bond with one another rather than with water. This also helps preserve the food, by leaving less water available for microorganism growth.
Here, too, balance is important. With too little sugar, jelly and jam won’t completely set. With too much, it will be rubbery. Excess sugar may also recrystallize as crunchy nuggets when the mixture cools.
Jellies and jams are usually highly sweetened—one cup of sugar for every four cups of juice is a typical ratio. To make a low-sugar version, often called a fruit spread, you have several options. You can slightly reduce the sugar in a regular recipe. This produces a softer consistency, which some people prefer. You can also buy a type of pectin that includes a powdered, positively charged form of calcium that takes the place of the acid. Because no sugar is needed with this product, a preservative is added to the pectin.
Some recipes replace pectin with gelatin dessert mix. They may use a sugar substitute also. These sweeteners break down with prolonged heating, however, so the jars cannot be processed. These aptly named “freezer jams” are kept refrigerated or frozen instead.
explore our Web site. To report a technical problem with this Web site, please contact the