In Kentucky, bourbon demand is expected to double in the next five years, while the state’s cattle population has now reached its lowest point since 1951. Here’s how these two facts could combine to turn bourbon distilleries into a new source of biofuels.

At the end of the bourbon distilling process, producers are left with a substance known as stillage. This material consists of the grains used to feed the yeast that created the bourbon as well as dead yeast cells and other fermentation products. It is a high protein material and is most commonly used to feed cattle and other livestock. In Kentucky alone, 127.2 million gallons of bourbon were produced when the last comprehensive count was done in 2020 and for each gallon of spirits made, there is 10 times as much stillage produced.

While reusing that stillage as animal feed certainly helps reduce waste from the distilling process, transporting it can come with a significant carbon footprint. Sometimes the stillage is treated to remove solids from liquids and further refined to turn the liquids into what’s known as a syrup that can enhance existing feedstocks. But even though this syrup is more eco-friendly to transport, producing it is an energy-intensive process and many small-volume distillers – which make up 60% of the distilleries in Kentucky – simply don’t have the ability to carry out the process.

On top of that, according to a report from the US Department of Agriculture, beef herds in the country are at their lowest since 1951, meaning that using stillage as feed in the first place is becoming a less and less viable option for distillers.

Seeking a better solution for the use of the waste product, researchers at the James B. Beam Institute for Kentucky Spirits in the UK investigated turning it into the natural gas, methane.

Because bourbon stillage consists of “mash bill” – a range of grains that includes corn, barely, rye, and wheat – they conducted a series of experiments to see how different combinations of those grains would react when fed to anaerobic bacteria. They found that mash bills with higher rye content led to the lowest production of methane, while those with a higher corn content produced the highest methane yields.

Jordan Strickler, Martin-Gatton College of Agriculture, Food and Environment/University of Kentucky

Methane that escapes into the atmosphere is implicated as one of the prime sources of global warming. But when it is burned, it burns cleaner than coal and leaves the atmosphere faster than carbon dioxide. Therefore, it is often tapped as a “cleaner” fuel source, which means that turning the stillage into the gas could allow it to be used to power distillery plants, fuel trucks, heat homes, or generate electricity.

“This study shows that not only can distilleries help alleviate the environmental burden of excess stillage, but they can also create a circular system where waste turns into fuel,” says team leader Tyler Barzee, assistant professor of Biosystems and Agricultural Engineering at JBBI. “This is a local solution that could position Kentucky as a leader in both bourbon and renewable energy.”

The study Barzee and his team undertook has been published in the Journal of Environmental Management.

Source: University of Kentucky