Two Coopering Traditions
It wasn’t until the 17th century that European winemakers came to appreciate the contribution of wooden oak barrels to the flavor of their contents, and began to adjust the manufacture of barrels to enhance the most desirable traits. And across the Atlantic, coopers in the New World applied their Old World skills to the crafting of barrels from a different species of oak, harvested from the vast American white oak forests.
In time, two related traditions of coopering grew up, one to serve primarily the European wine industry, and the other to cater to American distillers. The differences between them persist today, as the makers of alcoholic beverages, including brewers, still put them to specific uses.
The difference starts with the trees. French oak―technically either Slovenian oak (Quercus robur) or sessile oak (Q. petraea)―the traditional choice for wine barrels, has a fine grain and high porosity. Because of the nature of the wood, French oak has to be hand-split along the grain, which preserves capillaries in the wood. American, or white oak (Quercus alba) is a more robust tree, and American loggers saw, rather than split, the logs, probably permitting stronger flavors to eventually leach out of the barrels.
“The difference between French oak and American oak is also the difference between a wine barrel and a bourbon barrel,” explains Paul McLaughlin of Kelvin Cooperage. The Kentucky company was founded by his father, a cooper trained in Scotland. “The key is that the wood for a wine barrel is air-dried for at least two years before they make it. The idea is that you allow the wood to sit out in the elements, exposed to wind, rain and sun, and you’re leaching out the harsh tannins―the more astringent elements that you can get in a really oaky wine that makes your lips pucker.”
The American oak, by contrast, is quickly kiln-dried, with more of the stronger compounds remaining behind. This difference only becomes accentuated as the cooper constructs the barrel.
Once the staves―the long boards that make up the sides of the barrel―are raised into a barrel shape and secured in place, both types of barrels are heated to cultivate the right flavors in the wood. “The big difference in wine versus whisky is that with a wine barrel you slowly toast the barrel over a small oak fire where it can sit for up to an hour,” says McLaughlin. “With a whiskey barrel, you’re going to char it heavily, usually over a gas element: you’re literally setting the inside on fire. The char gives it a smoky flavor, something on a wine barrel you’d avoid. The key difference, of course, is that whisky can handle a lot more than wine can.”
After testing the barrels for liquid-tightness, the barrels are sent to their first users. The French wine barrels arrive precisely toasted to maximize the oak flavors that emerge at different heating regimes to favor vanilla, caramel, almond, coconut and “oakiness.” The American bourbon barrels, with their heavy layer of char and underlying layers of toasted wood, are ready to permeate a relatively neutral spirit with color, and a super dose of those same flavors, augmented with smokiness, cedar or coffee notes.