The ingredients that are in the most basic forms of jelly include fruit, sugar and pectin, which allows the jelly to form a gel like substance. In commercial jelly, preservatives may be added and additional substances can be added to enhance and increase the flavor of the jelly.
Many jellies will also include some type of acid, such as citric acid obtained from the juice of a lemon, to help protect the fruit from decomposing and fermenting. Additional acid is not used in fruit that is extremely ripe or fruit that already has a high acid content because the acid contained in the fruit is enough to help the pectin form the gel substance.
Fresh fruit is the most common type of fruit to use when making jelly. The fruit can be irregularly shape and is able to have irregular colors within it, as long as it has not gone bad. The fruit is sliced, mashed and combined together with other ingredients so the way that the fruit looks will not make a difference. Sugar must always be used to ensure that the pectin is able to set. Artificial sugars should not be used when making jelly because they will not cause the chemical reaction that allows the pectin to set.