Used wine barrels let the beer shine (spirits barrels add more of their distinctive flavor whereas wine has a mellower flavor than spirits). Wine is low enough in alcohol that bugs such as Brettanomyces and Lactobacillus can survive within the staves. Unlike the case of many spirit barrels, vintners often refill wine barrels several times. Repeated batches of wine draw out much of the wood’s raw character before it accepts the new beverage. Furthermore, wood is porous and admits a slow trickle of oxygen over time. That oxygen, along with certain sugars within the wood itself, provides a cozy environment for Brettanomyces, making the wine barrel an excellent choice for Sour / Wild beers barrel aging.