What wine production technique did the Celts introduce around the first century C.E.?

The technique introduced by the Celts around the first century C.E. primarily involved the use of oak barrels for storage and transportation. This method significantly enhanced the aging process of wine, contributing to improved flavors and complex aromas. Oak, being a porous material, allows a small amount of oxygen to interact with the wine, which is essential for the development of tannins and other flavor compounds during aging.

The ability to store and transport wine in oak barrels also facilitated trade and distribution, helping wines to reach broader markets. This innovation was a notable advancement over previous methods, such as using clay amphorae, which while effective for fermentation and storage, lacked the beneficial aging properties imparted by oak. This advancement by the Celts in barrel-making techniques set the stage for the widespread adoption of oak barrels in winemaking throughout Europe in subsequent centuries.