(CNN Business)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.
Whisky-powered vehicles
Biofuels aren't new. In the late 1800s, Rudolph Diesel experimented with peanut oil as the original fuel for his namesake engine, and in the 1930s, Henry Ford saw plant-based ethanol as the "fuel of the future."
But using crops was costly, and oil provided an inexpensive alternative. Tangney's goal was to find a cheap base material to make biofuels commercially viable — as well as more sustainable.
He set up the UK's first biofuel research center at Napier University in Edinburgh, Scotland, in 2007, and explored "everything from newspaper to seaweed" before settling on whisky by-products. Seeing the commercial potential, Tangney formed Celtic Renewables in 2011 as a spin out from the university.
The startup uses a process known as acetone-butanol-ethanol (ABE) fermentation in which bacteria break down the sugars in the whisky draff and pot ale into acids. They in turn are further broken down into solvents such as butanol and ethanol, which can be added to petrol or diesel to power a car. Celtic Renewables has demonstrated its fuel, driving an unmodified Ford on Scottish roads using 15% biobutanol made from whisky.
Tangney says his fermentation process isn't limited to whisky by-products, and could use waste from other food sectors such as dairy. "That's where we see ourselves as adding value," he says.
In 2021, Celtic Renewables built Scotland's first biorefinery in Grangemouth.
A viable solution?
Biofuels made from renewable organic materials such as corn, soya beans or sugarcane, are often promoted as a low-carbon alternative to fossil fuels, but producing them often requires huge amounts of land, which can detract from the benefits of reduced greenhouse gas emissions, says Alison Smith, a senior research associate at the Environmental Change Institute at the University of Oxford.
As aviation and other industries look to biofuel as a quick solution to decarbonize, Smith warns that there are "huge trade-offs and impacts on biodiversity, carbon storage, and food security," depending on the raw material.
However, fuel made from "genuine waste" such as whisky by-products is "probably the best possible kind of biofuel" she says, as it avoids these problems. Tangney has commissioned an independent life cycle analysis of his product to evaluate its environmental benefits, to be published later this year.
Scale is also an issue. With biofuels currently accounting for just 3% of the fuel used in global transport, they have a long way to go before they will make a serious dent in carbon emissions and greenhouse gases.
Instead, the transport sector should emphasize reducing demand, says Smith. "That makes it much easier to supply the rest of our transport needs from sustainable sources, whether that's renewable electricity or biogas or liquid biofuels," says Smith.
Beyond waste-based fuels
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%.
Glenfiddich Distillery has been converting its whisky by-products into biogas since 2008. Now, it uses this biogas to power its trucks, as well as the distillery's operations.
Whisky waste can be used to create more than biofuels. The solvents from its fermentation can be used as an alternative to oil in plastics, cosmetics, pharmaceuticals, clothing and electronics, says Tangney.
Celtic Renewables has raised more than £40 million ($52 million), with backing from private investors, government grants, and crowd funding, in addition to support from Napier University, which remains a shareholder.
The company built Scotland's first biorefinery last year, with the capacity to convert 50,000 metric tons of whisky by-products into biochemicals. Tangney says the plant will be fully operational later this year once testing is complete.