Squeeze the grapes in a cold juicer; that gave me 1.5 liters of grape juice. Bring the water with the crumbled cinnamon and star anise, clove, cardamom, allspice, coriander and rum to the boil and pour through a sieve into the juice. Pour the juice into a sufficiently large saucepan, stir in the preserving sugar and the remaining ingredients and bring to the boil for a few minutes. Pour the jelly into sterile jars, close immediately.