BARREL SCIENCE: Tinkering with barrels allows distillers to experiment with new whiskey flavors.
Image: Courtesy of Buffalo Trace Distillery
Master distiller Harlen Wheatley of Buffalo Trace Distillery draws a bourbon whiskey sample out of the barrel and pours it into a brandy snifter glass. Wheatley raises it into the light; the bourbon illuminates with rich colors of caramel, gold, straw yellow and light brown. He tastes the seven-year-old drink known as W. L. Weller and says, "That's really coming along."
As Wheatley moves onto the next barrel, the glass sits in the light, the bourbon shining brightly and illustrating the chemical change wrought by the barrel. After being poured into the barrel, the colorless spirit sat there or "aged" for seven years. The liquid mingled with the wood, giving the bourbon it's color, taste and smell.
A new generation of distillers have begun to break time-honored tradition and tinker with the barrels, relying on science and experimentation to bring new flavors into the spirits. For the bourbon whiskey business, the barrel is everything.
Bourbon barrel science
All bourbon is whiskey, but not all whiskey is bourbon. Congress declared bourbon "America's Spirit" in 1964 and, according to the Federal Alcohol Administration Act, bourbon whiskey must be produced from a fermented mash of at least 51 percent corn, although malted barely, rye or wheat can be added to the mash. Once distilled, the clear spirit must be stored at not more than 125 proof in charred new oak containers. Coopers have long built bourbon barrels out of American white oak, specifically the species Quercus alba, instead of the popular-for-wine French white oak or other common oaks.
American white oak's durability as well as its ability to hold water and oxygenate it make it favorable for bourbon barrels. American oak is denser and harder than French oak, making barrels less prone leakage. Q. alba also yields different flavor profiles appealing to the U.S. whiskey market, says Brad Boswell, whose Independent Stave Company makes the majority of U.S. whiskey barrels.
"American oak has lactone levels certainly not found in French oak," Boswell says. Lactones, a molecule in oak wood that imparts taste, yield a coconut flavor that can be controlled by cooking, toasting and seasoning the wood. Before a barrel is assembled, barrel pieces called staves air dry either indoors or outdoors. This process slowly degrades the wood "because of the microbial activity that grows and feeds off the wood. The rainwater, snow and the natural elements leach the [bitter] tannins out of the wood," Boswell says.
Once air-dried, the staves form a 53-gallon barrel that is later charred to filter out organosulfur compounds that are not eliminated in the distilling process. Distillers pour fresh distillate into the new, charred oak barrel, and the change begins.
Pressed into the wood
At the chemical level, the wood's lactones, sugars, tannins, cellulose, hemicellulose and lignins interact with the esters, aldehydes, butanols and two-methyl butanols to give the whiskey flavors of vanilla, caramel, spice, toast, smoke, coconut, coffee and mocha. Vapor and barometric pressure push the whiskey deep inside the wood, bringing out more intense flavor notes. Wheatley says the higher a barrel is in a several-story warehouse, the more pressure the barrel exerts on the liquid, pushing it deeper inside the wood. "When it's real hot outside with high pressure you hit the side of the barrel and the bung [stopper] will shoot up four or five feet," Wheatley says. "If it's cold outside with low pressure, it's hard to get the barrel bung out. It will just sit there."
Such observations are valuable for Wheatley and others who have dedicated their careers to studying the complexities of bourbon whiskey. For 200 years distillers did not have the science or perhaps the desire to test the limits. They just followed the procedures and practices from distillers before them: Make spirit from fermented mash, age in new charred oak barrel and bottle.
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4 Comments
Add CommentLarger barrels would have a smaller "surface-to-whiskey" ratio than smaller barrels. This is because "surface" increases as a square function while "whiskey" (volume) increases as a cube. Thus, a barrel that holds twice as much whiskey only has only 1.59 times as much surface. The "surface-to-whiskey" ratio decreases by 21% for the larger barrel vs. the smaller barrel. This does account for the "extra" wood staves in the larger barrel, since the depth to which the whiskey can penetrate would be a constant and again vary primarily due to surface area.
Reply | Report Abuse | Link to thisA couple points to dispel the marketing hype...
Reply | Report Abuse | Link to thisFirst, *larger* barrels of the same relative dimensions have *less* surface-to-area ratios than smaller barrels.
Second, given that the altitude relative to sea level of the Kentucky distillery is probably under 185 meters, the barrels near sea level are only experiencing about 2% more atmospheric pressure ("Oceanic air pressure" is a marketing blurb) than at the company's other storage facility. Realistically, storage at higher temperatures and its effect on the vapor pressure of the liquid is the factor most responsible for any higher pressure in a barrel. Even less significant, and I'd call it negligible, is the difference in air pressure for barrels stored at different heights in the same warehouse. If one wanted to 'drive more whisky into a barrel's wood', one could simply pressurize the barrel.
About the only science this story gets right is that temperature affects the pressure inside the barrels and that different woods exchange different compounds with the whisky.
Sorry, one thing to add...
Reply | Report Abuse | Link to thisThe claim that storing casks at sea level helps increase the pressure, driving more of the whisky into the wood strikes me as being perfectly backwards.
If the casks are bunged at higher altitudes the relative pressure inside the barrels will generally be lower than the atmospheric pressure at sea level. The pressure-driven flow would be in the opposite direction claimed. If the casks were bunged at seal level, there would be practically no starting differences in pressure and so being at sea level would add no change to the net flow in or out of the wood.
It's ironic that distilling spirits helped drive the science of thermodynamics but the spirit marketing departments embrace voodoo to sell it.
The lively experimentation in American whiskey is a magnificent thing. All sorts of new things are being tried. Some work, some don't, but the stuff that works brings us new and interesting spins on a time-tested idea.
Reply | Report Abuse | Link to thisTake this for example: an American single malt smoked with mesquite instead of peat!
http://whiskeyreviewer.com/2013/03/ranger-creek-mesquite-single-malt-set-for-release/