In making apple jelly it is not necessary to peel the apples, but simply wash them, cut them up and remove the blossom end. Sour, juicy apples are the best, or crab apples. Add just enough water to barely cover the fruit - about 3 cups of water to each pound of fruit will be required for all hard fruits, such as apples, quinces, guavas, watermelon, etc., whilst for soft, juicy fruits, such as strawberries, mulberries, and grapes, very little, if any, water should be used.
Allow to cook until quite tender, keeping the lid of the saucepan on, then strain through a sieve or piece of butter muslin. If a nice, clear jelly is desired, it is necessary to strain the juice again through a flannel or felt jelly bag, otherwise the jelly will be cloudy; and for that reason, too, it is not advisable to mash the fruit or to try to hasten the process by forcing it through the bag.
After the juice has dropped through, measure it, pour it into an enamelled saucepan, and boil it for 15 to 20 minutes, being careful to remove any scum that may form. In the meantime take the sugar, allowing 1 cup of sugar to every cup of juice (as a rule the apple contains a lot of pectin, and therefore this is a safe proportion), put it into an enamelled basin in a moderately hot oven, and allow to warm through thoroughly, stirring it every now and then. By heating the sugar a superior jelly is obtained, for if the sugar is added cold it reduces the temperature of the juice, and so will take longer to reach the jellying stage, thus darkening the product. Add the hot sugar to the juice and stir until thoroughly dissolved, then leave undisturbed and allow to cook rapidly until the jellying stage. It is difficult to say how long to boil, as it depends on the amount of pectin present and sugar used. Usually it takes from 10 to 20 minutes, but some fruits take even longer.