Then they can drain and dry out completely. The bacteria, yeasts and molds that grow so profusely on the bottoms of old dirty wine bottles represent a constant source of contamination. Consequently, dirty, used wine bottles should not be stored in winemaking areas. Dirty bottles should be washed and sterilized and stored away in a sanitary condition. Maintaining empty oak barrels in good condition is difficult.
Small producers burn sulfur wicks in their empty barrels.
Large wineries fill their empty barrels with sulfur dioxide gas from high pressure cylinders. Experienced winemakers avoid empty barrels by immediately refilling them with new wine.