The step in the process of making Madeira that involves heating the wine. Depending on the quality of the Madeira being produced, there are several estufagem methods. The most basic involves placing the FORTIFIED base wines in containers that are then heated to an average temperature of 113°F (with a maximum temperature of 131°F allowed) for three to six months. To make the very finest Madeiras, however, the containers may be placed in a warehouse attic, which builds up tremendous heat thanks to the intense Madeiran sun. There the Madeira-to-be may be left for twenty years or more.