It has fuelled rain-soaked Highlanders for centuries, but now a distillery in northeast Scotland has found another use for whisky -- to power lorries.
In a warehouse at the bottom end of The Glenfiddich Distillery in Dufftown, draff -- one of the by-products of whisky making -- is tipped out of the back of a truck into a steaming pile.
The soaked barley grains will be combined with a yellow, beer-like liquid called pot ale, another residue of the distilling process, before an anaerobic digester is added to produce a low-carbon biogas.
The gas, which is primarily methane, is stored in tanks in a yard around the corner, where specially adapted trucks can refuel. "The process involves taking our waste products -- pot ale and draff -- from the distilleries and turning that into gas that can then fuel vehicles," distillery site manager Kirsty Dagnan told AFP. "So we now have vehicles that can transport our goods and our spirits around the country using a renewable source that is ultra-low carbon."
Fuelling stations have been installed at the distillery and the biogas is now powering converted trucks that handle the transportation of the spirit at all stages of its production, Dagnan said.
Each truck that uses the new biofuel will save around 250 tonnes of carbon dioxide from being emitted into the atmosphere, she added.
Researchers at Edinburgh Napier University in 2010 announced they had developed a biofuel using the spent grains and liquid from the copper stills. It was hailed at the time by environmental campaigners for being made without causing damage to forests and wildlife.
"Whisky-powered cars could help Scotland avoid having to use those forest-trashing biofuels" such as palm oil, said WWF's then Scotland director, Richard Dixon. According to William Grant & Sons, the distillery's parent company, biogas significantly reduces carbon dioxide and other more harmful emissions compared to diesel.
The process is widely used, but is the first time it is being used by a distillery to power its trucks. So far, three have been adapted to use the biogas. They will transport Glenfiddich's spirit from production at the Dufftown facility on Speyside, northwest of Aberdeen, to separate bottling and packaging sites in central and western Scotland.
The company plans to expand the technology to all its 20 trucks and eventually to roll it out to the rest of the industry.
"When you take into account the cost of purchasing the truck and then running it and maintaining over its life and the cost of the fuel, actually it's a very similar cost to do that for biogas as it is for diesel," said Stuart Watts, director of the company's distilleries.
"This makes a compelling choice for companies such as ourselves to use the biogas truck rather than the traditional diesel truck."
At the refuelling yard, a truck driver cautiously presses the nozzle into his gas tank. It takes roughly the same amount of time to refuel as it would to fill up with diesel and the range of a journey is similar, he says. With the tank filled up, the nozzle hisses as the driver removes it from his tank and he heads out into the Highlands under rain.