Wash the fruit and place in pan with sufficient cold water to cover; bring slowly to a boil and simmer until skins burst. Press carefully with potato masher just enough to finish opening all the fruit. Do not press or mash hard or a bitter flavor results. Strain through a soft cloth or jelly bag. Let drain without pressing the bag of fruit. Measure the juice and put equal amount of sugar into a jelly kettle (tall enough that it won't boil over).
An enamel-lined pan is preferable to aluminum, or stainless steel is good. Stir only until the sugar is melted, then bring to a full rolling boil. Jelly is ready when it falls in very thick, heavy drops from a spoon and almost sets before it drops.
For a tart jelly to take the place of cranberry sauce to be served with meats, use only half the amount of sugar.