Work by evolutionary biologists, ecologists, and geneticists has shown that humans and fungi actually have a great deal in common. On a recent trip to Kentucky I discover one more commonality, a love for bourbon. 

Last October my boyfriend (fellow scientist) and I traveled south to Kentucky to explore bourbon country. At our first stop we saw many things we expected to see at a distillery, silos to store the corn, rye and other grains used to produce the bourbon, large stills to purify the liquor, and warehouses full of bourbon-filled oak barrels in various stages of the aging process. One thing we noticed and did not expect, but struck our curiosity more than anything else, was a strange, black, soot-like residue on many of the surfaces outside the buildings of the distillery. It was everywhere; on tree leaves, warehouse siding, fence posts. As we continued on our first tour, moving from building to building, our fascination with this substance grew. 

Like good scientists, we started to propose possible explanations. We learned that the oak barrels are charred on the inside before they get filled with bourbon. This thick, burnt layer provides flavor and color as the white dog ( one of the names given to the freshly distilled bourbon) ages. Could it be possible that this black residue is a result of the barrel charring process, producing bits of soot that scatter and land throughout the distillery? Or maybe this particular distillery had previously caught on fire. Besides charring the inside of the barrels, heat is needed to make the sour mash (the thick mix of boiled grain and water that is subsequently fermented by the yeast) and to purify and distill the liquor. With this much heat, alcohol, and wood around, it seemed feasible that a past fire could have caused this layer of soot across the distillery. We left open the possibility that this substance could be biological, but allowed for the simplest explanation as we finished our bourbon tasting and headed to the next distillery. 

When we arrived at the second distillery, many miles away from the first, we were stunned to find this black coating again! We decided to rule out distillery fire as a possible cause. What were the chances that two distilleries, miles apart, had both experienced catastrophic fires so intense that a layer of soot remained years later? The barrel charring process still made sense and seemed likely. By definition, bourbon is a whiskey that is aged in new, charred, oak barrels, so every bourbon distillery must go through the same process or charring the inside of their barrels. 

While we had, what seemed to us a reasonable explanation, the idea that this could be some sort of biological organism could not escape our minds. Unfortunately, we were nowhere near Ohio State where we could try to grow some of this substance in the lab to test if it was living. We considered setting up a makeshift experiment to try to culture the material, but decided that was more the bourbon talking and continued to enjoy our tours. On the third and last day in bourbon country, we visited my boyfriend's favorite distillery, Wild Turkey. Once again, we noticed this black residue everywhere and were finally bold enough to ask our tour guide, "What is this stuff?". That is when we finally learned about Angel's Share fungus. 

The angel's share is a common term used in distilleries that refers to the alcohol lost to evaporation during the bourbon ageing process. The barrels of bourbon remain in the warehouses for years while ageing, and overtime the alcohol content of the bourbon decreases as the ethanol evaporates through the tiny cracks and crevices in the barrels. It turns out that another organism takes advantage of this gaseous ethanol, the fungus Baudoinia compniacensis or more commonly called the Angel's share fungus. This fungus is able to grow on a variety of surfaces and feeds on airborne ethanol. A distillery is a perfect place for B. compniacensis to call home since airborne ethanol is abundant. 

We also learned that this fungus was problematic for bootlegger during prohibition. Local law enforcement was able to locate hidden distilleries by the presence of this fungus on trees and surrounding buildings. Thanks to the 21st amendment, the relationship between the angel's share fungus and distilleries like Wild Turkey is now a purely amicable one, and visitors like myself get to witness this interesting biological phenomenon while imbibing their favorite bourbon. 

Written by TPS Fellow, Katie D'Amico