Maderisation is the (controlled or uncontrolled) process of exposing wine to heat and oxidization, which in turn darkens the colour and alters the taste. The winemaking-term takes is name from the controlled process used in the making of Madeira wine, where it occurs while the wine rests in oak barrels. The wine as mentioned darkens to richer shades and acquires a unique character and flavour profile.
When not refering to Madeira wine - it is generally seen as a fault, but at controlled levels is desired in certain dessert wines where it occurs over the course of lengthy ageing. The term Maderised (or oxidised wine) - is derived from the French word Madère - meaning Madeira and thus Madérisé, meaning oxidised, the process by which Madeira is deliberately made.

 

A maderised white wine will have a yellow to pinkish hue, whilst a red wine will turn tawny. Oxidation is the reaction of oxygen with various components in wine. When oxidation occurs during the winemaking process, the winemaker is able to treat the condition by using sulphur dioxide or ascorbic acid. However, there are many styles of wine which are deliberately oxidised, such as Madeira, Sherry, Vin Santo, Rancio, Vin Jaune and other styles vinified ‘sous voile’ - literally under a veil, for example the thin layer of yeast referred to as 'flor' which forms on the surface of Fino Sherry.
The style of Madeira wine was previously achieved by long ship journeys to tropical countries. The wine endured hot condistions that changed its character, the so-called maderisation. In the 18th century ‘estufajes’ were built. These are vessels in which the wine is heated for 3 months to a minimum of 40ºC up to a maximum of 50ºC. The wine is slowly brought to temperature, with a maximum of 5°C per day.
The creator of this system was Pantalão Fernades - inspired by ancient Roman baths. After warming follows the ‘estagio’ a resting period for at least one year - and up to 10 years. There are two types estufa: the ‘Armazen the colour’, warming in wooden barrels, and the ‘cubas the colour’ warming in plastic of ceramic vessels of 20,000 to 40,000 litres.
Bual or Boal in Portuguese is a name given to a number of different varietals grown on the island of Madeira and also refers to the style of wine produced. The grape has a high acidity which works extremely well when put through the 'maderisation' process where the wine is fortified and then slowly cooked in the barrel over a number of years (traditionally the barrels are placed in the attic where they get nice and hot during the summer days and cool off during the night). The slower the maturation proceeds, the better the wine becomes.
When the winemaker feels that the character of the wine is sufficiently formed, step by step the barrels will be moved to lower levels until it is on the cool floor of the winery. Keeping the barrel constantly at high temperatures would be too costly, because of the evaporation of the wine - every year the winery loses about 1.5 - 4% of wine by evaporation, the so-called angels share. This slow aging system called ‘Canteira’ is the basis of all quality wines. Canteira is the name of the wooden beams on which the casks rests.
They also use a unique solera process, which resembles the Sherry system, but not exactly the same. As in the Madeira solera system - the wine can stay for decades in wooden casks. Occasionally some wine is taken off and sold, up to 10%. The cask is then refilled with new wine. This gives a wonderful blend of flavours: the old wines provide intensity and complexity; the young wines give vibrant freshness. After 10 times draining and refilling the entire cask must be bottled at once.
These wines attain amazing longevity and it is rare but not that unusual to find centenarian bottles or even older. These older wines have a wonderful combo of sweetness, acidity and texture with a delicious caramel, molasses and green apple flavours that seem to last forever on the palate. All 3 year old Madeira wine is produced in estufajes. The caramel-like character from this young Madeira makes it very suitable as an aperitif, also used in the kitchen for soups, sauces and stews, being today’s most exported style of Madeira wine.