Already oxidized and pasteurized, Madeira is built to last. Perhaps that's why a Madeira from 1834 can hold up so delightfully well, nearly two centuries after it was first produced. In either case, the estufagem system is one of three modern processes used, with a second variation essentially steaming the cask warehouse for six months to a year or longer, and the final involving only natural heat over a period of decades, generally producing what is seen as today's best and most expensive Madeiras.