What’s Happening in the Barrel?

How differences in weather conditions affect whiskey aging in Bourbon Country
inside the Maker’s Mark aging cave

All photos by Maggie Kimberl. 

If you’ve ever been on a distillery tour in Bourbon Country you’ve heard the same basic thing about why Kentucky is the most perfect and magical place on Earth to age bourbon – the summers are really hot, which drives the whiskey into the wood, and the winters are really cold, which pulls it back out. It’s this process that gives bourbon all of its color and a lot of its flavor. The water in the whiskey dissolves the wood sugars while the charcoal filters out all the undesirables. Pretty simple, right? Not so fast.

Maker’s Mark Has Studied Aging Extensively With Independent Stave

Independent Stave explains it better than anyone I know,” says Maker’s Mark Maturation Specialist Jane Bowie. “There are basically four primary things that happen: addition, subtraction, oxygenation, and reaction. Addition is the one everyone really thinks of – you’re extracting the wood components into the distillate. You’re pulling everything out of the barrel. Subtraction, when you char the barrel you’re pulling out some of the undesirable things with the charcoal. Oxidation people don’t fully understand yet – basically when oxygen and water and alcohol and all these things get together it’s going to create new compounds – that’s esterificiation. Oxygen and airflow are big, not only for climate but also for what’s happening in the barrel. Reaction is about all of those chemical reactions that are happening in the barrel, and people are still learning about everything that is going on in there. Alcohol is more soluble with certain compounds and water is more soluble with certain compounds. Certain compounds are going to only be created in certain environments.”

Maker’s Mark aging cave exterior

Different weather conditions cause different compounds to enter the whiskey, says Bowie. “It goes back to those reactions. Furfural is one of those compounds that gives you those caramel aspects. It becomes more soluble in warmer temperatures. I have learned this from our cooperage partner. We have spent a lot of time figuring out which compounds come from the wood and the fact is in many cases we still don’t know. That’s one of the things that is so romantic about maturation – it’s just so natural.”

Tannins are another flavor compound that enters the whiskey in hotter temperatures, says Bowie. For this reason an extended hot summer or too many summers can have a detrimental effect on maturing bourbon. It’s also why Maker’s Mark built a man made cave to age its Maker’s 46 line of products.

“The cellar is underground because 46 needs that cold temperature,” Bowie explains. “The way we cook those staves the tannins are really locked in. The reason we built the cellar is to make 46 year round in the cooler temperatures so those tannins aren’t being released.”

Across The State, Buffalo Trace Built An Experimental Warehouse

Buffalo Trace experimental Warehouse X

In 2006, a tornado ripped the roof off of Warehouse C at Buffalo Trace Distillery in Frankfort. As the damage was assessed and eventually repaired, dozens of barrels of bourbon sat at the top of the rickhouse completely exposed to the elements. A few years later it was bottled and labeled as “Tornado Surviving Bourbon,” and there was something about it that people went wild for. This inspired Buffalo Trace to build Warehouse X, where they could conduct various experiments on the maturation process of bourbon that included controlled variants in temperature, light and more.

Inside Warehouse X there are five separate chambers with sensors that monitor the conditions day and night. After more than two years there has been only one phase of the study completed with 3.5 million data points collected.

So what have these experiments told us about how different elements impact the maturation process of bourbon? According to Master Distiller Harlan Wheatley, “What it has proven is that you can change the environment and change the whiskey.  Ventilation, temperature, humidity, etc. all play a part.”

monitoring the barrel temperature at BT

Knowing that, it stands to reason that changes in weather patterns can have an impact on the end product that comes out of the barrel, but how much? If the weather becomes atypical for a year or two, is there a noticeable difference?

“For us,” says Wheatley, “most of our products are aged longer than our competition so the immediate changes affect our bourbon slightly less. Over the long haul it is an average of exposure to the atmosphere. So we take a look at 7 or 8 years of the environment to see how it changes the whiskey.”

In other words, it all evens out in the end.

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