The vanilla orchid attaches itself to trees, and the seeds are found in longish pods hanging from the plant. The complicated process of pollinating, growing and then curing this aromatic spice makes it one of the most expensive in the world. The orchid flowers only for a few hours. Women known as marieuses hand-pollinate up to 1,000 blooms a day. The pods take six weeks to reach full size, and another six to nine months to mature.
The green pods, which have none of the familiar vanilla flavour or fragrance, are then cured - a three-to-six-month process that begins with a 20-second boiling-water bath, followed by heating by the sun. They are then wrapped in blankets to sweat (which activates enzymes to create the rich aroma) and finally dried to a deep-brown or black colour.
The plants like moderate shade, not too much sun, and just the right amount of humidity. Vanilla is mainly grown on the east coast of the island between Ste-Suzanne and St-Philippe. In the town of St Andre, just in from the coast, is La Maison de la Vanille, an old Creole mansion set amid lawns, gardens and plantations, where you can trace the history of this increasingly popular flavouring.
l La Maison de la Vanille, on the rue de la Gare in St Andre, Reunion, is open from Tuesday to Sunday, 9am-noon and 2-6pm.
l Reunion is a trekkers' paradise, and the Lonely Planet guide to Mauritius, Reunion and the Seychelles (pounds 10.99) devotes an entire chapter to it. Recommended is a two-day trek from the scorched summit of the volcano, Piton de Fournaise, down to the sea where a footpath takes you past "vanilla plants lazily wrapping their tendrils around filao trees".
l It is not that common to find vanilla from Reunion on sale in the UK. Birgit Erath, who runs the Spice Shop at 1 Blenheim Crescent, London W11 (0171-221 4448) reckons that vanilla from Madagascar, 800km away, is every bit as good. She has vanilla from Mexico and vanilla pods in bottles of Bourbon - which she says is great for pouring into coffee.
l Most vanilla-flavoured food has never been near a vanilla pod - it is usually flavoured with vanilla substitutes. But Sainsbury's has just launched Organic Madagascan vanilla ice-cream (price pounds 2.49 for 500ml, available from Monday).