The system consist of the use of vessels (named “boots”) made out of american oak , with a capacity off in between 250 and 600 liters. Periodically a percentage of the content is taken out of each of these “boots” to fill in others. In specifically the “boots” are situated in three heights. From the inferior boots approximately a quarter of its content is taken out for consumption. The missing amount of the inferior boots is obtained and filled up with the contents of the intermediate height boots. And in the same way the intermediate level ones are filled with the superior. The superior are filled with new wine (or “holandas” for the production of brandy). This system permits that the quality of the product is very high and homogeneous, because in all the boots there is big amount of old wine (or brandy) that “cheats” ( gives body) to the wine that has been added more recently ( either it is new wine or already aged wine in a superior boot). That is why the wines from Jerez and of Montilla-Moriles never have a vintage date; each bottle that is consumed has a unique mixture of wines of different years that have aged together until forming a homogeneous wine.