title_body: Maturation process in casks
upvoted_answer: Liquor casks are not cleaned between transfers, just emptied and stored until they need them again. The liquor that soaked into the wood makes sure nothing will grow in them.
  
  Wine barrels on the other hand, need to be cleaned between transfers. Typically they are rinsed with hot water and then maybe steam. Left to drip dry for a day or two. Then sulfur dioxide is put into the barrel either through a gas or burning sulfur in the barrel. This sterilizes the barrel. 
  
  Many wine/sherry casks are reused as Whisky barrels. Minimal amount of cleaning is need before the strong alcohol is put in them (which sterilizes them).