Experienced winemakers use their noses, and they discard any barrels smelling of vinegar. Empty barrels can be safely stored for several weeks if they are gassed with sulfur dioxide and kept tightly sealed. Home winemakers and small commercial wineries burn sulfur wicks in their barrels. Large wineries purchase sulfur dioxide gas in high pressure cylinders. Barrels gassed with sulfur dioxide should be washed with clean water before they are filled.
Winemakers face another serious problem when empty barrels are stored for long times.
After several weeks, the wood in an empty barrel becomes dry, and the staves start to shrink. As the wood shrinks, the hoops become loose, and the barrel loses its shape. In hot, dry climates, barrels often fall to pieces in a few months. At best, empty barrels leak badly when first filled, and several days of soaking are often required before these barrels can be filled with wine. Barrels can be maintained for extended periods if they are stored wet.