The method of vinification is similar to that employed in other parts of Portugal, but the method employed for hastening the maturation of the wine is peculiar and characteristic.
This consists in subjecting the wine, in buildings called estufas specially designed for this purpose, to a high temperature for a period of some months. This process is meant to duplicate the effect of a long sea voyage of the barrels through tropical climates. Madeira was originally unfortified, but the addition of grape spirits increased its ability to survive long voyages.
The temperature varies from 100° to 140° F. according to the quality of the wine, the lower temperature being used for the better wines. The buildings in which this process is carried out are built of stone and are divided into compartments heated by means of hot air derived from a system of stoves and flues.
Much of the characteristic flavor of Madeira is due to this practice, which hastens the mellowing of the wine and also tends to check secondary fermentation inasmuch as it is, in effect, a mild kind of pasteurization. Furthermore, the wine is deliberately exposed to air, causing it to oxidize. The resulting wine has a color not unlike a tawny port. Wine tasters sometimes describe an oxidized wine as being "maderized."
Exposure to extreme temperature and oxygen accounts for its stability; an opened bottle of Madeira will survive unharmed for a considerable time, up to a year. Properly sealed in bottles, Madeira is one of the longest lasting wines; Madeiras have been known to survive over 150 years in excellent condition. It is not uncommon to see Madeiras pushing the century mark for sale at stores that specialize in rare wine.
Before the advent of artificial refrigeration, Madeira wine was particularly prized in areas where it was impractical to construct wine cellars (such as parts of the southern United States) because unlike many other fine wines it could survive being stored over hot summers without significant damage. A favorite of Thomas Jefferson, it was held in high enough esteem to be used to toast the Declaration of Independence.
There are four major types of Madeira: Malmsey, Boal, Verdelho, and Sercial, the latter two being drier. Occaisonally one sees Terrantez. Madeira may be sold as a vintage wine with a specific year, or a solera wine with a minimum age, such as 10 years.
Madeira wine is prominently featured in the Flanders & Swann song "Have Some Madiera, M'Dear".
See also: Malmsey