A Look at How Weather Affects Whiskey

July 22, 2017

The flavor of a whiskey is dependent on many factors, including the percentage of grains in its mashbill and the type of wood (or woods) it ages in. Distillers carefully consider these options when making whiskey, but one major factor they can’t control is the weather. Unless the whiskey has the luxury of resting in a temperature controlled warehouse—an extremely rare occurrence—weather plays a critical part in the outcome of the final product.

A Trip To The Kentucky Bourbon Affair

I attended the Kentucky Bourbon Affair which takes place in early June each year, hosted by the Kentucky Distiller’s Association. This is a consumer event that gives enthusiasts a chance to visit distilleries and participate in activities that are not typically open to the public during regular tours. So instead of merely being escorted into a warehouse to look at dusty barrels and peering into mash tuns, etc., we got to see and taste for ourselves what really happens to bourbon behind the scenes.

Weather Affects Whiskey: Between RickhousesBetween Heaven Hill Rickhouses / Photo Credit: Heaven Hill

One of the most fascinating afternoons took place at the Heaven Hill compound. We were given the rare opportunity to sample identical single barrel whiskeys that were housed on different warehouse floors. This was all to experience how different zones in the same building affect bourbon maturation. The aging whiskey is stored on several levels of the warehouse, where the wooden floorboards are set wide apart to allow the air to circulate. The top floors are the hottest and most humid, and the bottom floors are the coolest, darkest and driest. Temperatures can actually vary as much as 15 degrees between lower and higher floors.

Why does the weather affect the outcome?

Consider that a water molecule is quite small. Since it’s much hotter on the higher floors, heat causes the water to evaporate from the barrels much faster. This causes the alcohol proof to rise in the barrels. On the cooler, lower floors, water is more likely to penetrate the barrel from surrounding moisture, which lowers the proof.

Weather Affects Whiskey: Barrel Entering RickhouseBarrel Entering Rickhouse / Photo Credit: Heaven Hill

The “control bourbon” was Evan Williams Single Barrel, put into oak in 2006. We tasted it on the seventh floor, then the first, then the fourth—each at cask strength. The bourbon from the upper most floor was noticeably richer and more dense. It also had the most alcoholic bite at around 139 proof. The one from the bottom floor was far more tame in comparison. Its flavor showed more of the bourbon’s cereal, spice and fruit notes on the forefront at 121.1 proof. The bourbon on the fourth floor, which for many in the group was their Goldilocks whiskey (just right!), was drier and spicier with sharper herbal notes at 121.3 proof.

Location matters

Barrels are also quite heavy, so when they’re stored, they aren’t moved from their location until they’re ready to be emptied. To offer a more consistent product, the majority of bourbon is a blend of different batches. At the new Bulleit Frontier Whiskey Experience, located at the former Stitzel-Weller distillery, some of the warehouses are not as tall and vast, but we saw that the concept is very much the same. The bourbon placed toward the front gets more direct sunlight and heat; the ones in the back stay cooler.

Rickhouse with sunbeams

Bulleit Bourbon, like many bourbons, is blended from some whiskey that was stored under hotter conditions, and some from cooler conditions, at different ages, then blended together to contribute to the final flavor profile. For special releases, some distilleries, such as Four Roses and Buffalo Trace, reveal which proprietary recipes they pulled from (though not in detailed measurements) and at which warehouses the liquid was stored. This way consumers have a better understanding of what goes into the final the blend.

So the next time you sip a bourbon on a warm day, consider what all that pleasing glass of nectar has been through for you. You think it’s hot out? Try being a top floor bourbon barrel for a summer! Luckily you don’t have to.

Armed with your new knowledge, let’s go whiskey hunting!

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