That 15-year Macallan you’ve been saving for a special occasion has a dark side: It was extremely inefficient to produce. The Scottish malt whiskey industry currently disposes of 90 percent of the liquid it produces because it is undrinkable.
Scotland-based startup Celtic Renewables wants to change that. Whiskey byproducts — known as draff and pot ale — can be converted to biobutanol, a biofuel that provides 25 percent more energy by volume than ethanol. It is also safer to handle and can be blended with gasoline at a higher concentration to run in unmodified engines. To top it off, it evaporates less easily, meaning it would have a lower impact on air quality than ethanol.
Scotland’s $6.2 billion malt whiskey industry produces more than 4 million gallons of pot ale and 550,000 tons of draff annually. Pot ale is a liquid produced during the mashing process, while draff is husk residue left by fermented grains.
Celtic Renewables is halfway through its pilot program, which will determine if producing biobutanol from whiskey is cost effective. They will produce 2,600 gallons of biofuel in the process. Tullibardine, which makes single malt Scotch whisky, is providing them with pot ale and draff. If all goes well, Celtic Renewables would also like to convert waste from the wine, beer, wood processing and food prep industries.
Like ethanol, biobutanol is made with fermentation. Bacteria is added to break down draff and pot ale into products like butanol, acetone and ethanol. Celtic Renewable also plans to convert solids produced during the fermentation process into animal feed.
Biofuels are made from biological materials like corn, algae and soy beans. Liquid biofuel makes up about 1 percent of the U.S.’s energy, according to the Energy Information Administration. There has been a large push for ethanol use, which fell flat due to the fuel’s questionable sustainability. Today, it accounts for more than 9 percent of U.S. gasoline and is the most common biofuel.