Sauternes is a sweet white wine that comes from a particular region of Bordeaux, France. Unlike Bordeaux's other white wine, Graves, Sauternes is generally made from a mixture of Sémillon and Sauvignon grapes.
Its characteristic honeyed sweetness and deep gold color is an effect of noble rot, or Botrytis cinerea, a fungus which shrivels grapes on the vine, resulting in a high concentration of sugar and flavor. Botrytis, known as the grey rot when it's not wanted, grows especially well in the wet, misty Sauternes region -- and when cultivated, it can flourish.
As with most French wines, the name Sauternes is only given to wine that meets a very strict list of criteria which includes the region in which the grapes are grown. Purists may note that the name Sauterne lacks both the trailing 's' and the nod of the appellation d'origine controlée, and some insist that it only refers to inexpensive wines from California, US -- though it's common for English-speakers to use the Anglicized term to refer to both the French Bordeaux and California varieties.
The best Sauternes come from vineyards that hand-pick perfectly moldy grapes off the vine at the perfect moment, scorning any fruit not thoroughly shriveled and fuzzy. Possibly the best-loved Sauternes is Château d'Yquem; there, grapes are harvested over the course of weeks, and each vine is visited an average of three times by pickers looking for grapes at maximum botrytisation. A combination of laboratory analysis and careful attention to weather patterns is used to determine the ideal period in which to pick the grapes. Unsurprisingly, Yquem's yields are unusually low -- whereas most Bordeaux varietals produce about a bottle-per-vine, Yquem boasts one glass per vine.
Primarily a dessert wine, a glass of Sauternes -- preferably a small, tulip-shaped glass, whose narrow opening funnels vapors straight to the nose -- can also be served alongside rich flavors like Foie Gras.