Kate Humble's journey takes her from the Atlas Mountains of Morocco to the plains of Spain as she uncovers the story of the world's most expensive spice, saffron, before crossing the Atlantic to Mexico in search of vanilla, a spice discovered by the famous Spanish conquistador Hernan Cortes.In the Atlas Mountains, October is saffron harvest month for the Berber people. Kate joins local saffron farmer Ahmed and his family to harvest their crop and visits a stunning store house carved into the mountainside.Worth 4,000 pounds a kilo, saffron is also known as red gold and inspires countless imitations. In Spain, Kate turns detective as she joins a blind tasting to sort out genuine saffron from the fakes and meets a man who tests its DNA in order to make sure it's genuine.The Berbers of Morocco took saffron to Spain in the Muslim conquest of the 8th century, and 800 years later it was an ambitious Spaniard that brought us the next exotic taste, vanilla. It's now so widespread that it has become the world's most popular ice-cream flavour.Kate journeys to Paplanta in Mexico, the birthplace of vanilla, to meet the Totonac - the original guardian of the spice. She witnesses a spectacular death-defying fertility dance and meets the people determined to keep Mexican vanilla alive in the face of the massive competition from other producers.