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 crafted from chestnut wood instead of oak, which resulted in high levels of tannins and a porous structure that facilitated excessive evaporation within the barrel. Under this traditional method of winemaking, a significant air gap (ullage) would develop in the barrel, leading to oxidation.