1.Place fruit, the water, sugar and butter in a large saucepan over medium heat; stir constantly until butter is melted and sugar is dissolved. Increase heat to high; bring to the boil. Reduce heat; simmer, uncovered, for 8 minutes. Stir in soda. Cool to room temperature.
2.Transfer cooled mixture to a large bowl; stir in eggs, sifted flours and spice and rum.
3.Fill a boiler three-quarters full with hot water, cover with a tight-fitting lid; bring to the boil. Prepare one cloth at a time: wearing thick rubber gloves and using tongs, dip pudding cloth into boiling water, then boil for 1 minute. Remove cloth, squeeze out excess water. Quickly spread hot cloth on the bench; rub ¼ cup of the extra plain flour into the centre of the cloth, leaving the flour a little thicker in the centre.
4.Divide pudding mixture evenly between pudding cloths; place the mixture in a mound in the centre, keeping it within the floured area. Gather the cloth evenly around the mixture, avoiding any deep pleats. Tie cloth tightly with kitchen string as close to the mixture as possible.
5.Fill the boiler three-quarters full with hot water; bring to the boil. Lower puddings into boiling water, tie string to pan handles; boil rapidly for 4 hours, replenishing with boiling water as required (the water must not go off the boil).
This pudding can also be steamed in eight 1-cup (250ml) pudding steamers. To store, wrap the puddings in plastic wrap; seal tightly in freezer bags or an airtight container and place in the fridge or freezer. You will need kitchen string and eight 30cm squares of unbleached calico. If the cloth is new, soak in cold water overnight, then boil for 20 minutes; rinse well before using.