Company, this method involves storing the wine in large wooden casks in a specially designed room outfitted with steam-producing tanks or pipes that heat the room, creating a type of sauna. This process more gently exposes the wine to heat and can last from six months to over a year. Cuba de Calor: The most common, used for low-cost Madeira, is bulk aging in low stainless steel or concrete tanks surrounded by either heat coils or piping that allow hot water to circulate around the container. The wine is heated to temperatures as high as 130 °F (55 °C) for a minimum of 90 days as regulated by the Madeira Wine Institute. However, the Madeira is most commonly heated to approximately 115 °F (46 °C) Barrel-aging process: Canteiro: Used for the highest quality Madeiras, these wines are aged without the use of any artificial heat, being stored by the winery in warm rooms that are heated only by the warm climate of the Madeira island. In cases such as Frasqueira (vintage) Madeira, this heating process can last from 20 years to even more than 100 years. The term Canteiro comes from canteiros - the wooden staves that keep the barrels in their places. Canteiro process is used by all of the top Madeira brands, including Blandy's, Borges, Broadbent, d'Oliveiras and Justino's. Much of the characteristic flavour of Madeira is due to this practice, which hastens the mellowing of the wine and also tends to check secondary fermentation in as much 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 colour similar to a tawny port wine. Wine tasters sometimes describe a wine that has been exposed to excessive heat during its storage as being cooked or maderized. Styles The noble varieties The four major styles of Madeira are synonymous with the names of the four best-known white grapes used to produce the wine. Ranging from the driest style to the sweetest style, the Madeira types are: Bual (also called Boal) has its fermentation halted when its sugars are between 2.5 and 3.5° Baumé (45-63 g/L). This style of wine is characterized by its dark colour, medium-rich texture, and raisin flavours. Malvasia (also known as Malvazia or Malmsey) has its fermentation halted when its sugars are between 3.5 and 6.5° Baumé (63-117 g/L).