The 2009 Doppelmagnum ex-château refers to a large-format bottle (3 liters) of Château d'Yquem 2009 that was sourced directly from the estate (ex-château), without intermediaries. This large bottle format, known as a Doppelmagnum, is equivalent to four standard bottles (750 ml) and is highly prized for its aging potential, as the wine in larger bottles tends to develop more slowly and gracefully than in smaller ones due to reduced oxygen exposure.