Scrape the seeds from the vanilla bean into a large pot, then add the bean and all the other ingredients. Cover with 850ml cold water and bring to the boil. Reduce to a low heat and continue to simmer for 10 minutes.
Turn off the heat, cover the pot with a lid and leave to infuse for a further 20 minutes. When ready to drink, strain and serve, or transfer to your fridge once cool and drink cold.