About 44 bottles of Scotch whisky are shipped around the globe every second, making it the world's most internationally traded spirit and generating export revenues of £4.5 billion ($5.9 billion) last year.
But for every liter of whisky, there is a huge amount of waste: around 2.5 kilograms of solid by-products known as draff, 8 liters of liquid known as pot ale, and 10 liters of spent lees, a watery residue. This amounts to 684,000 metric tons of draff and over 2.3 billion liters of pot ale every year, according to Zero Waste Scotland. Some is used for animal feed, and some goes to landfill or is dumped in rivers and oceans.
One biofuel scientist has come up with a creative, high-value use for this waste. Martin Tangney, founder of Celtic Renewables, uses a fermentation process to transform whisky by-products into biochemicals that can replace some of the petrol and diesel used in cars, and can be used to make other oil-based products, too.
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There are already whisky-powered vehicles driving around Scotland. Glenfiddich Distillery, operated by William Grant & Sons, uses biogas made on-site from the by-products of its own whisky to power some of its trucks, reducing the trucks' carbon emissions by 90%
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