Jelly making consists in cooking fruit juice with sugar until, upon cooling, it will solidify, or jell. While this is not a difficult nor a complicated process, there are some housewives who do not have success with it. Often the result may be very good when a certain fruit is used, whereas it may be entirely unsatisfactory at another time, even though the same fruit is used and practically the same procedure is followed. If the best results are to be assured in jelly making, the principles that are involved in this process must first be thoroughly understood and then the correct procedure must be painstakingly followed out.
To solidify properly and thus become a desirable jelly, the fruit juice that is used for this purpose must have the following characteristics and treatment: (1) it must contain certain jelly-making properties; (2) it must be extracted properly; (3) it must be combined with the correct proportion of sugar; and (4) it must be cooked the proper length of time. There are, of course, numerous degrees of solidity of jelly, varying from that which will barely retain its shape to that which is very tough and hard, but neither extreme is desirable. To be right, the jelly should be firm enough to stand up well, but should be tender and soft when a spoon is cut into it.
Fruit is the principal ingredient in the making of jelly, as it is the source from which the juice is obtained. Such imperfections in fruits as poor shape or unattractive appearance do not count in this matter, since only the juice is used; but they must contain jelly-making properties in order that jelly can be made from them.
Green or slightly unripe fruits are better for jelly making than fruits that have become ripe. In fact, when in this immature state, fruits may be used to make jelly, whereas the same fruits, when perfectly ripe, often will not make jelly at all, or, if they do, will produce a jelly that is inferior in quality.
The chief requirement of fruits that are to be used for jelly making is that they contain acid and pectin. Pectin is the real jelly-making property of fruits. When it is in the presence of acid and combined with the correct proportion of sugar and the combination is properly boiled, a desirable jelly is the result. Without pectin, however, it is impossible to make the juice solidify, or jell. Pectin is closely related to the carbohydrates, but as it does not yield heat energy nor build tissue, its food value is not considered. In this respect, it is like the cellulose of fruits and vegetables.
It is because green fruits contain more pectin than do ripe fruits that they are more suitable for jelly making. The lack of either acid or pectin need not, however, prevent the making of jelly from fruits, such as sweet fruits, that contain other jelly-making properties, for either or both may be supplied from some other source. In other words, jelly may be made from any fruit that will yield juice and flavor.