The marrow should be very, very firm and too tough for cooking or cutting with a kitchen knife. Saw through the stalk end, and scoop out the seeds and pulp. Fill the marrow completely with sugar. Put the top back and tape it tightly in place. Put into a bag made of strong cloth and hang it in a cool, dry place. After two weeks, fill the marrow again with sugar. Seal the top again and hang up the marrow. After about a month, the sugar will begin to drip. Take the marrow from the bag and make a hole in it where the sugar is starting to drip. Let the liquid run through a muslin-covered funnel into bottles. Cork them lightly. Fermentation will soon start. When it has ceased (in a few weeks) cork firmly. Keep for at least a year before using.