After 5-6 years, our big oak barrels require cleaning. The surface layer of wood (0.1-0.2 inches) needs to be removed so that the wine is in contact with renewed wood. This is not an easy task, which is why we use a highly specialized external company. In the video below you can see a worker inside the barrel.
The barrel, after the planing, is washed with water (photo above) and then filled again with wine.