When your wine has stopped fermenting, you have to rack it off into another demijohn to get it off the yeast. Dead yeast decays and will give a strange flavour to the wine if you don't.
So I did, and at the same time I topped it up with a little water that had been boiled in the kettle, and added a little sugar. The wine promptly turned a green colour, rather like pea soup.
However it did eventually clear into a pale yellow pee-colour, and this I then transferred to bottles, where, according to the instructions, you have to leave it for a year before drinking it. I have to admit that I tried a bit. I hope that ageing improves it.