Traditionally the barrels were made of chestnut instead of oak, which contributed high amounts of wood tannins and was very porous which promoted excessive evaporation in the barrel. Under this same traditional style of winemaking, a large ullage or air space would emerge in the barrel and oxidation took place.
Traditionally, barrels were made from chestnut wood instead of oak, which led to high levels of tannins and a porous structure that promoted excessive evaporation within the barrel. This traditional method of winemaking resulted in a large air gap (ullage) forming in the barrel, leading to oxidation.