This section is from the book "Everywoman's Canning Book", by Mary B. Hughes. Also available from Amazon: Everywomans canning book; the A B C of safe home canning and preserving.
One secret of quick and perfect jelly is to have everything hot which comes in contact with the jelly. Add the sugar after heating it (on a platter in the oven is often the most convenient way), and have the jelly glasses standing in hot water, ready for the jelly as soon as it is ready to take from the stove. Have everything at hand before putting the fruit juice to boil.
With a wooden potato masher or spoon, crush soft fruit, such as raspberries, strawberries, grapes, etc., in a saucepan, add just enough water to prevent burning, and heat slowly over the fire. When hot throughout (do not let fruit boil) pour into a jelly bag and let drip. The jelly bag may be suspended from the backs of two chairs, or in any clean and convenient place where it will be out of the way.
Hard fruits, such as apples, quinces, peaches, plums, pears, etc., are prepared for jelly making as follows: Wash; do not remove skins; cut up and put in a saucepan, cores, seeds, and all. Barely cover with water and cook until soft. Drain in a jelly bag until the pulp is dry. Do not press the bag. Four to six hours is usually long enough to let fruit drain.
To make a second extraction, return the pulp from the jelly bag to the saucepan, add enough water to prevent burning, and heat through. Return to the jelly bag and let drip. This second extraction may be combined with the first, if desired. The alcohol test for pectin will show whether the second extraction will make jelly, or be fit only for fruit juice.
To make a good jelly, fruit juice should taste about as tart as a sour apple. If juice is found to be lacking in acidity, add a little lemon or other acid fruit juice. The addition of acidity improves not only the flavor, but the texture of the jelly. This is true of jelly made from flavorless apples, quinces, blackberries, and blueberries.
Jelly pulp may be cooked with a little water, spices and sugar added to taste, and made into a fruit butter.
Measure the fruit juice before putting it over the heat, bring to the boiling point quickly, and boil eight minutes. Skim just before adding the sugar, and then as needed.
To each quart of juice add three-fourths of a quart of sugar which has been heated. There are three exceptions to this general rule, blueberries, green grapes, and currants. With these juices allow equal measures of sugar. Stir until the sugar is dissolved, then boil rapidly from three to five minutes.
Make jelly in small quantities. One quart or three pints of fruit juice is enough to make into jelly at one time. Such quantities can be handled more safely and successfully. If one desires to make more jelly, have two saucepans over the fire, with a quart of juice in each.
The most reliable and the simplest test by which to know when to take jelly from the stove is called the two-drop test. A little experience in this method gives one a safe guide for all time. Take a little of the boiling syrup on a tablespoon, after the sugar has been cooked in it for three minutes, and pour the syrup from the side of the spoon above the kettle. When the jelly is done, the syrup will form in two large, thick drops at the side of the spoon before falling off. Remove at once from the fire and pour into jelly glasses, which should be standing in hot water.
A single layer of damp cheesecloth placed over the top of the glass may be used as a strainer, in case some of the white coating from the sides of the saucepan is floating in the jelly.
Jelly may be made on a rainy or cloudy day, as well as when the sun shines brightly.
If jelly does not seem firm enough after it is cold, let it stand for a few days in the hot sun, covered by a piece of plain window glass.
Honey may be used in place of sugar, with equal measures of fruit juice and honey.
Give great care to the jelly bag, especially those made of felt. See that the bag is scalded and hung out of doors in the sun after use. Any sourness about the jelly bag imparts a flat, insipid taste to the fruit juice. Fruits are sometimes blamed for their lack of good flavor, when a poorly cared for jelly bag is really the cause.
When making jelly in the winter, it is well to let the fruit drip from the jelly bag near a hot stove or radiator. The pectin in the fruit juice causes the bag to stiffen when it is cold, and if the fruit becomes chilled, a great deal of the juice is lost in this way.
When the jelly is cold, melt a little paraffin in a saucepan and pour over the top. Be sure that the paraffin touches the edge of the glass all around. A tablespoon of melted paraffin is enough to cover and protect the jelly. Great, thick coverings of paraffin are unnecessary and wasteful. Tip the glass after putting on the paraffin, in order that it will reach the edges all around. Another method is to cut white paper to fit the glass above the jelly. Dip the paper in brandy before putting on top of the jelly. Either of these methods will protect jelly indefinitely. When jelly is for immediate use, the brandy is superfluous.