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, Calif.

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.

The monetary value has. Barrels are expensive, and they don’t last long. They’re relegated to the garden after about five years of use. At the few French cooperages with Napa Valley facilities, such as Seguin Moreau and Calistoga’s Nadalie USA, American oak barrels with lumber originating from forests in Missouri and Pennsylvania run about $400; Eastern European barrels cost close to $700, and the highly coveted French oak barrels from the forests of Vosges and Troncais fetch nearly $1,000.