Every liter of Scotch whisky leaves a mess behind it. For each liter of the spirit, a distillery produces roughly two and a half kilograms of spent barley grains \u2014 called draff \u2014 and about eight liters of a warm, coppery liquid called pot ale, the dregs left in the still.<\/p>\n
Multiply that across an industry that ships dozens of bottles of Scotch around the world every second, and the leftovers are staggering: almost 750,000 tonnes of draff and two billion liters of pot ale<\/a> a year. It is whisky\u2019s dirty secret \u2014 some of it becomes animal feed, some is spread on fields, and plenty has historically been dumped in rivers and the sea. Getting rid of it is a permanent line on every distiller\u2019s budget.<\/p>\n A Scottish company looked at that river of warm barley soup and saw a fuel depot. The trick was to hire the right microbes.<\/p>\n The century-old fermentation that came back<\/p>\n The process at the heart of it is not new \u2014 it is a resurrected antique. Acetone-butanol-ethanol fermentation, ABE for short, uses a bacterium, Clostridium acetobutylicum, that eats sugars and starches and excretes a mix of three solvents: acetone, butanol and ethanol.<\/p>\n ABE fermentation was a giant of early-twentieth-century industry \u2014 it made the acetone Britain needed for munitions in the First World War \u2014 and then the petrochemical boom undercut it, and it nearly died out. Celtic Renewables, a company spun out of Edinburgh Napier University\u2019s biofuel research center by Professor Martin Tangney, revived the old chemistry and pointed it at a feedstock the Victorians never had: distillery waste.<\/p>\n Draff and pot ale are, from a bacterium\u2019s point of view, a banquet \u2014 spent grain still rich in sugars, and a nutrient-loaded broth. Feed them to Clostridium, and the microbes do the rest, converting whisky\u2019s garbage into industrial solvents by simple biological digestion. The company built Scotland\u2019s first biorefinery beside the petrochemical complex at Grangemouth to do exactly this at scale.<\/p>\n The fuel that needs no new engine<\/p>\n Of the three products, butanol is the prize, because of a chemical accident of fit.<\/p>\n Most biofuels come with an asterisk. Ethanol \u2014 the corn-based additive in ordinary gasoline \u2014 carries less energy than petrol, absorbs water, and can corrode or degrade parts of an engine not built for it, which is why pumps cap it at a blend percentage. Biobutanol has none of those problems: its energy content and chemistry sit close enough to gasoline that it can, in principle, go straight into an existing engine as a direct replacement<\/a>, no modification required.<\/p>\n Celtic Renewables proved the point on the road. In 2017 the company ran an unmodified car on Scottish roads<\/a> using biobutanol made from whisky residue \u2014 a Ford burning, in effect, refined distillery slops, with nothing changed under the hood. Tangney\u2019s line for it was the oldest one in recycling: one man\u2019s waste is another man\u2019s gold.<\/p>\n Why leftovers beat crops<\/p>\n The deeper argument for the whisky plant is what it is not doing, and it lands on the central complaint against biofuels generally.<\/p>\n First-generation biofuels \u2014 ethanol from corn, biodiesel from soy or palm \u2014 have a land problem: growing fuel crops competes with growing food, and clearing ground for them can erase the carbon savings the fuel was supposed to deliver. Draff and pot ale sidestep the objection entirely. Nobody grows barley to make draff; the draff already exists, in vast quantity, as an unavoidable by-product of a thing the world was going to make anyway. The feedstock is free of the food-versus-fuel dilemma because it is the leftover from the food. Turning it into fuel doesn\u2019t cost an acre.<\/p>\n The honesty column is real too. The plant so far operates at demonstrator scale, its output a rounding error against national fuel demand; ABE fermentation is finicky and historically hard to make pay against cheap oil; and Celtic Renewables has broadened its pitch from \u201cbiofuel\u201d toward higher-value sustainable chemicals \u2014 bio-acetone and bio-butanol for paints, pharmaceuticals and, eventually, aviation fuel \u2014 precisely because the economics work better there than at the petrol pump. The company\u2019s next Grangemouth facility, backed by fresh investment, is designed to process far more waste and to take in other food-industry leftovers, potatoes and dairy residue among them, not whisky alone.<\/p>\n But the core image holds, and it is a small marvel of circular design. Scotland makes its most famous export, and the export makes a mountain of warm barley waste. Rather than pay to dump the waste, the country can now, in principle, feed it to bacteria and pour the result into the fuel tank of an ordinary car. The whisky industry\u2019s embarrassment becomes its second product line \u2014 and the microbes doing the work are running a chemistry humanity used a hundred years ago, rehired to eat the one thing Scotland will never run short of.<\/p>\n About this article<\/p>\n This article is for general information and reflection. It is not professional advice. For your specific situation, consult a qualified professional.<\/p>\n Follow Space Daily on Google<\/p>\n Add us as a preferred source to see more Space Daily reporting in Google.<\/p>\n \t\t\tAdd as preferred source<\/a><\/p>\n A personal measure of deep time<\/p>\n \t\t\tSee what has changed in the universe since you were born.<\/p>\n Begin with one date. Get a personal, sourced journey through everything that kept moving after you arrived.<\/p>\n Six sourced measurements. No predictions. No astrology.<\/p>\n Standards<\/p>\n \n\t\t\t\tSpace Daily articles are edited and fact-checked before publication. We use AI tools in the newsroom. See our editorial standards<\/a> and masthead<\/a>.\n\t\t\t<\/p>\n","protected":false},"excerpt":{"rendered":"Every liter of Scotch whisky leaves a mess behind it. 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