Although it’s proverbially wine that’s known for getting better with age, we all know it is the same with whiskey. Even more so, whiskey doesn’t even turn into whiskey without the ageing and flavoring processes, which simultaneously happen inside the “magic”barrels. I’ve touched upon the subject quite a few times before, especially when talking about Tennessee whiskey and Kentucky Bourbon, but I find it a very complex topic which I could write many posts about.
After leaving the whiskey still, the raw liquor, moonshine at this stage, enters barrels for ageing. The wood is where the whiskey gets about 40-70% of its distinctive aroma and color. Maturing is the ultimate goal, not a specific age but, it’s a general rule that the older the whiskey, the stronger the flavor. Wood to whiskey ratio is also very important, as the bigger the contact surface, the stronger, or quicker to obtain, the flavor. What is interesting to observe during visits to distilleries is that, no matter how many revolutionary, accurate, modern equipment has come out in the past decades (gas chromatographs, mass spectrometers and computersthat can break down chemical components to the very last cell), it is still a man-mastered art, completely dependent on a skilled master distiller and his senses.
For American whiskeys, the standard whiskey barrels of 53 gallons are made from new white oak. American white oak's durability, as well as its ability to hold water and oxygenate it, make it favorable for whiskey barrels; the wood is denser and harder than French oak, making barrels less prone to leakage. French oak also has a different flavor profile, it’s spicier; the wood is also lighter, allowing oxygen to interact differently with the spirit. In United States, the barrels have to be new so that as much of the flavor as possible gets soaked out of the wood by the whiskey and many commercial distilleries now re-barrel their whiskey in new charred oak barrels to reinforce the wood notes.
For drying the new oak staves, before turning them into barrels, some choose to use a kiln, which is obviously faster, but many distilleries still use the traditional, natural option of air-drying. They usually leave the wood outside for 9-12 months as they believe exposure to the elements prepares it much better for its next task: flavoring. The exposure is believed to reduce the level of certain chemicals which are unfavorable to the whiskey aroma. This is not a general rule though, as some distilleries also air-dry their wood indoors.
Back in the day, the wood was held over fire to make it easier for it to bend and turn into barrels. In time, the fire was replaced with steam. Although steam was much more efficient for softening the wood, whiskey makers discovered they were missing some of the flavors that originated from the fire. That’s why, today, barrels are toasted on the inside: the process modifies the wood’s chemical components, turning some into sugars. The sugars caramelize in the heat and give the whiskey its caramel-vanilla sweetness and its amber color. It’s also where the smoky flavor comes from. The charring process, which we’ve seen before with bourbon, is different from the toasting. It’s an additional quick burning of the inside of the barrel, which produces more caramel and creates a thin charcoal layer which filters the liquor during its maturation.
Once the moonshine’s out of the copper whiskey still and moved into barrels, the maturing process begins. Many distilleries have observed that storing their freshly-filled whiskey barrels at the top of the warehouse for the first 2-3 years, helps exert more pressure onto them. In this way, the spirit is pushed deep inside the whiskey, bringing out more intense flavors. They then move the barrels in the lower half of the warehouse, where the temperature variations throughout the year are more moderate, compared to the hot top half. Other distilleries simply leave their barrels in place for the length of the maturation, then make a selection of barrels from the top and lower areas and blend them together. And for some, aging has even gone beyond stationary warehouses: such as Jefferson's Reserve with their Ocean-Aged Bourbon, which was left to mature on a ship for nearly four years. The founder of the distillery said the Panama Canal's extreme heat pushed the whiskey deeper inside the wood, causing the wood sugars to caramelize and add a rum-like black hue. He said the bourbon also breathed differently at sea, and the salt air added a unique briny taste to the whiskey.
Many distilleries have tried to come up with new, tastier or more interesting products. As seen with experiments like the one above, most distillers choose to alter the wood or the aging process. The Woodford Reserve Distillery put standard 6-7 year-old Woodford Reserve in a maple wood barrel as well as former sweet wine casks to lend more chocolate, nutty and dark cherry flavors not usually found in bourbon. The former fortified wine barrels had wine soaked into the wood and the fruity flavors that remained from the barrel's former alcohol enriched the flavor of the bourbon.
In an effort to create a spicier-finishing whiskey, Maker's Mark added toasted French white oak staves to its existing bourbon barrel for its 2010 Maker's 46 . When the bourbon hit the barrel and mingled with the French and American oak, it took on both woods’ profile characteristics and became a combination of French spice and American sweetness.
The owner of an upstart distillery from Ohio called Cleveland Whiskey decided the conventional method of producing whiskey simply wasn't fast enough to meet that demand. But rather than water down an existing recipe, he also started experimenting with wood. His new method: he ages the whiskey in a new oak barrel for the first six months, and then deposits it in stainless steel tanks. He cuts up the used barrel, processes the wood and adds it into the tank. In the tank, the spirit is agitated and undergoes a series of differences in pressure to squeeze in and out of the wood pores. After a week in the tubs, the hyper-aged whiskey is ready for bottling. Cleveland Whiskey hopes to produce 20,000 cases of the whiskey in 2014.
But the Buffalo Trace Distillery is said to hold the record for whiskey experimentation. Since 1987 the company has conducted more than 1,500 barrel experiments for its Experimental Whiskey collection. The tests included studying sections of the tree to determine which heartwood should go into which stave and making a French oak barrel three times the size of a standard barrel. In the latest experiment the distillery charred a regular bourbon barrel for 3.5 minutes instead of the standard 55 seconds.
The wood and the ageing are the points where the most important differences between American whiskey and Scotch whisky come up. Very few Scottish distilleries use new oak casks and most Scottish distillers don't even want new barrels since they claim the flavors from the wood would overpower the character of their distillate. Traditionally, 132 gallons sherry casks called butts have been used. But these became scarce during the Spanish civil war of the 1930s and that’s when many Scotch distilleries turned to used bourbon barrels as an alternative. Sometimes, other cask types like port, rum or wine are used as well. The process of re-filling whisky into a fresh cask for the final months of the maturation is called finishing. Most whisky casks are re-used several times by Scottish distilleries. During maturation, the spirit extracts flavoring and coloring both from the wood and the remains of the previous cask filling, which makes the flavor palette much wider. The longer it stays in the cask, the darker the whisky gets. But every cask is different: there are 5 year old whiskies that are dark brown, and there are 30 year old whiskies that are only slightly yellow.
Maturation, too, differs between American whiskey and Scottish whisky. Although Scotch can legally be sold once it is three years old, it’s usually decades that create distinction. But that is mostly to do with the climate. As an experiment, Maker's Mark swapped barrels with a Scottish distiller to see how much the environments of the two places affected the whisky's maturation. The experiment's outcome was that one year in Kentucky, with its hot summers and cold winters, was roughly equal to four in Scotland, with its much more constant and humid climate.
The list of experiments can go on for many more pages, but the essential process has been the same for centuries: fermentation, distillation, most often in a copper whiskey still, ageing and flavoring in new or “second-hand” wood barrels. And although the first two are key foundations for the final product, it’s the last two that give the spirit its unique flavor and distinctive notes.