The climate of Kentucky has always been a part of the production of Bourbon. The fact that corn grows better in Kentucky than rye is because of the climate. Rye grows better in a cooler climate like Pennsylvania whereas corn thrived in Kentucky. Corn became the staple crop of the settlers and thus what they distilled into whiskey. However that is just the beginning of how climate had an effect on the production of Bourbon.

Distilling was always done in the cooler months of the year. The distillers would start in the fall after the corn had been harvested and distill into winter and spring. They quit distilling in the warmer months because they quickly learned that the process did not work as well and they had smaller yields and the whiskey did not taste as good when it was made in the summer. As scientific knowledge advanced they learned that was because yeast would die sooner in the mash when it got too hot. Bacteria also grew better in the hot, humid months of summer. Technology in the form of a cooling system in the mash tubs, was invented in the 1860s and it extended the distilling season, but distilleries still found it better to shut down in the hot months of July and August. Advances in cooling technology allow the modern distillery to extend this period even longer, but even modern distilleries still tend to close down for a maintenance period during the worst heat of a Kentucky summer.

The hot summers and cold winters of Kentucky worked well for aging whiskey. The heat of summer causes evaporation in the barrel, forcing whiskey into the wood in the day and condensation at night as the barrel cools draws the liquid out of the wood bringing with it the flavors from the barrel. During the winter months the whiskey sat dormant as the temperature never rose high enough to create the pressure in the barrel for an “aging cycle”, so in the late 1800s some distillers started to heat their warehouses in the winter to increase their “aging cycles”.

Warehouse design also had an effect on this process. Multi-storied warehouses created microclimates with the top floors getting extremely hot in the summer while the lower floors remained relatively cool. This increased the evaporation of water on the top floors and had a larger effect from the wood of the barrel while the bottom floors lost more alcohol and had less effect from the wood. Distillers quickly learned that the bottom floors were better for aging whiskey for a longer period of time. The whiskey was better balanced with tannins and sugars than whiskey aged on the upper floors which would get too much tannin. Some distillers opted to rotate barrels to get a consistent product while others built single story warehouses for consistency. Others used these difference to create different flavor profiles for their brands.

In the modern world it is the small artisan distillers that have to pay the most attention to climate. Like the original distillers, they often don’t have the money to invest in cooling systems for mash tubs or heat cycled warehouses or even multi-storied warehouses. The local climate of these distilleries have an effect on their final product so they have to adopt their production to the climate. This means their final product may not taste the same as a Kentucky Bourbon from a large distillery, but it does mean the consumer gets some very interesting variations that they have never tasted.

Photos Courtesy of Rosemary Miller