To make jelly without added pectin, cranberries should be picked in the yellow stage when they are just turning red. To prepare juice, place cranberries in a Dutch oven. Add just enough water to cover. Bring to a boil; reduce heat and simmer, covered, until berries are soft. Strain through a jelly bag. Add 1 cup (250 mL) sugar for each 1 cup (250 mL) of juice. Stir until sugar is dissolved. Bring mixture to a boil and boil rapidly until jelly stage is reached. Remove from heat and skim foam if necessary. Pour into hot sterilized jars, leaving 1/4 inch (6 mm) headspace. Wipe jar rims thoroughly. Seal and process in a boiling water bath for 10 minutes.