The final episode takes in the Atlas Mountains of Morocco and the plains of Spain for the world’s most expensive spice, saffron, before crossing the Atlantic to Mexico in search of vanilla. In the Atlas Mountains, she joins a local saffron farmer and his family to harvest their crop. In Spain, she joins a blind tasting to sort out the genuine from the fakes and meets the man who tests the DNA of saffron. In Papantla, the birthplace of vanilla, she meets the Totonac, the original guardians of the spice. She witnesses a fertility dance and comes face to face with the people determined to keep Mexican vanilla alive in the face of competition from other producers

• Paul Sapin

• Kate Humble