Fire crackles between the seasoned oak staves, fastened with steel hoops. As the sparks settle, the aromas float through the air -- clove, cedar and vanilla. All the nonfruit characteristics you've ever identified in wine are coming to life here, in the warehouse of Seguin Moreau, a cooperage, or barrel making facility, in Napa. They're actually born long before that, as centuries-old timber in some of Europe and America's most precious forests. Through a laborious process that includes watering and firing, coopers turn the wooden slats into oak barrels, the spice racks of winemaking. Grapes alone don't make great wine. Juice needs a spine, and cooperages work with winemakers to customize fermentation barrels that achieve a desired wine style, whether it's a soft pinot noir or a big chardonnay. With the exception of mechanized sanding and a few quality control operations, the art of wine barrel making hasn't changed much in 2,000 years.