Barrels are more than packaging – they’re critical to the process of aging new whiskey. Once white dog is in the wood, the congeners, or toxins, generated during mashing and fermentation and retained during distillation, engage in a synergistic partnership with properties of the barrel wood; and with air and wind, cold months and hot ones, rainy days and drought, and with time itself. The raw, grainy white dog that entered the barrel clear as water emerges years later as an amber liquid suitable for sipping.

Federal regulations dictate that bourbon must be aged in new, charred, oak barrels. So, once they’re emptied of bourbon, most barrels are sold to distilleries in other countries and used for aging other products. Ninety-eight per cent of all Scotch is aged in bourbon wood as well as a few dark rums and tequilas. American white oak, or quercus albus to be specific, is the tight-grained hardwood used for bourbon barrels. White oak contains a substance called tyloses that naturally blocks the sap-conducting pores of the wood, giving it the right porosity for holding the whiskey while at the same time allowing it to breathe, which oxidizes and evaporates the congeners. A 53-gallon barrel is standard to the industry.

When I talked to Jimmy Banks in 2003, his job was visiting sawmills all over the country buying white oak wood that’s 75 to 100 years old for Bluegrass Cooperage. He carries a 14-inch hatchet in his briefcase. “You got to get into the wood,” he explains. The skin on his hands was thick as leather and he used a thumbnail to groove the piece of wood he held while explaining that the heads are flat sawn but the staves are quarter sawn to get the proper orientation of the growth rings and grain for maximum strength and leak resistance. “It’s bastard sawn if it exceeds 45 degrees,” he says.

The rough boards are sawed to a thickness of 15/16 of an inch and the soft outer layers of sapwood are ground off. The grinding eats up a lot of wood but the process is important because a sappy stave will taint the bourbon. The boards start out with a thickness of 5/4. “That’s 5/4,” clarified Banks, “not one and a quarter.”

The boards are stacked and seasoned for up to a year in open air but this time frame varies with distillery specifications. As it dries, the wood stabilizes by giving up moisture and lingering sap. After air-drying, the wood is kiln-dried then cut into staves for the sides and planks for the heads. The staves are shaped wider in the middle than at the ends and wider at the top than at the bottom to create the bilge of the barrel and make it liquid-tight.

The cut staves are ready for the coopers. “Raising” the barrel requires skill and experience. The cooper eyes and selects staves one by one as he begins standing them on end inside the circle of a heavy iron truss hoop lying on the floor. The bung stave, which will accommodate the bunghole, is the widest at four inches and it goes in first. The cooper snugs each one tightly to the next until the circle is complete with twelve to fourteen staves. The loose ends are pulled together with a temporary hoop and the barrel is placed on a conveyor that moves it to the steam box. A good cooper raises about 270 barrels a day.

Sometimes an exceptional cooper comes along. When one Charles Harden did this job at Bluegrass Cooperage, he raised 450 to 500 barrels every day, prompting a colleague named Spitty to observe “that boy’s not gonna last long.” Other coopers theorize that Harden could do this because he simply never made a mistake in his selection of staves. If they’re not fitting right, the staves are pulled out and the process begins again. Harden never had to start over.

The steam makes the wood pliable so the top end can be windlassed, or drawn together as tightly as the bottom end. This process bends the staves into the familiar bilge shape. The open-ended barrels are placed upright and conveyed into the toasting room. The insides are first toasted with a heated instrument for about 30 minutes to remove the surface moisture acquired in the steam box. The toasting also caramelizes the natural wood sugars. These sugars will leach into the bourbon during aging and flavor it with traces of caramel and vanilla.

When the barrels have toasted enough, the truss hoops are tightened and the barrel insides are literally set on fire for about 12 seconds to char. The depth of charring varies among distilleries with some preferring a light or medium char and others going for the deepest char, identified as a number 4. The heads are charred separately and placed on the barrel ends and the permanent quarter and bilge hoops are placed.

The barrels are cooled for an hour and all the hoops are tightened. The bung hole is bored and each barrel tested with a pressurized blast of water. Any showing leakage are turned back to hand coopers for repair. Charles Harden moved on to hand coopering.