|A good, science-y picture from a different UK CAER project.|
Stillage is a by-product of the distillation process. Unlike scotch, American whiskey is usually distilled from a mash, not a wash. In Scotland, Ireland, Japan, and most other places that make whiskey, solids and liquids are separated after all of the soluble starch in the grain has been liquefied. The liquid portion, known as the wash, goes forward into fermentation and distillation. The moist solids are considered waste and either used as animal feed or simply discarded.
In North America (U.S. and Canada) it is a little different because although the soluble starch is liquefied, just like in Scotland, the grain solids are not removed. Still known as mash it is a slurry, like a very thin oatmeal. It stays that way through fermentation and distillation. What comes out at the end of the process, after all of the alcohol has been removed through distillation, is stillage.
Keeping all of the solids adds flavor but American distillers do it mostly because they can. Since column stills are used for the first distillation instead of pot stills, the early removal of solids is unnecessary.
American distillers typically do separate their stillage into wet and dry components. It's a pretty simple process that leaves a few solids in the wet portion and a bit of moisture in the dry, but it is effective for its purpose. The wet portion is used as setback in the sour mash process. It is mixed with a new mash prior to fermentation. The wet stillage adds a little acid to the fresh mash, which the yeast likes, along with some yeast nutrients, which the yeast also likes.
Setback ratios vary but 1:3 is about the highest, so plenty of stillage is left over. The leftover wet stillage goes into the sewers. The dry portion (which is still pretty wet) goes to one of three places: (1) directly to farmers, who come and get it, for livestock feed; (2) processing that removes the rest of the moisture, which gives it a longer shelf life (it's still used as livestock feed); or (3) into the sewers.
The problem with stillage is that as a direct by-product of the process, the amount of stillage goes up as your production goes up. If there aren't enough nearby farmers willing to come and get it every day, option (1) isn't available. Although stillage is free to the farmer, the farmer has to pick it up and transport it. Even rural distilleries are having a hard time giving their stillage away under those terms, a problem that is compounded as the amount of stillage goes up.
Option (2) isn't great either because the processing (drying and other processes) needed to make the stillage something that can be packaged and stored is expensive. Although it's a good feed and does sell, as a product it barely breaks even, a situation that only gets worse as increased supply pushes the price still lower.
Option (3) is undesirable because not all municipal sewage systems can accept it and even when they can, it's adding to the waste stream when it could be used for something productive. If this project (which uses the wet portion) can find some new, value-added ways to use this material, that will be good for the whiskey industry and the environment.
Wilderness Trail Distillery is the natural partner for this project because it is a bourbon distillery run by scientists. The same folks own and operate Ferm Solutions, which supplies yeast and other products and services to distilleries in Kentucky and beyond. Formerly in downtown Danville, they have moved their operations to a new, much larger facility west of town. It is open to the public for tours.
That it is Wilderness Trail and not one of the majors involved in this is another example of how much the micro-distillery movement is contributing to the industry and to local communities.