Sterilization of barrels by burning sulfur wicks in otherwise closed barrels is called fumigation. The sulfur uses up oxygen from inside the barrel as it burns, forming sulfur dioxide (SO2). The combination of SO2 and lack of oxygen generally stops the action of yeasts and bacteria in a barrel. It is then necessary only to wash the barrel and refill it with wine for aging. Only with heavily infected barrels is it necessary to sterilize the barrel further. (Wine,Beer,Spirits,Sake,Mead/Production)