A century-old wartime recipe for making a chemical solvent has been pointed at the leftovers of Scotch whisky, and the result is a fuel that can run an ordinary car. Same microbe, same basic process. What changed is the reason for using it.

Let’s start with the wartime problem. In the First World War, Britain ran into a shortage of the chemicals needed to keep making shells. Its smokeless propellant, cordite, required acetone as a solvent, and wartime disruption cut Britain off from important continental supplies. What helped replace them was a bacterial fermentation process developed by Chaim Weizmann at the University of Manchester. A century later, an updated version of the same acetone-butanol-ethanol fermentation process was used to turn whisky-industry waste into biobutanol, which powered a car in a 2017 demonstration.

The two ends of that story don’t obviously belong together. One is about wartime munitions. The other is about a distillery waste stream nobody wanted. What connects them is a single microbe, and the odd fact that a technology shelved decades ago turned out to be exactly what a modern recycling problem needed.

The wartime origin of the process

The chemist was Chaim Weizmann, who later became the first president of Israel. At the time he was hunting for a way to make industrial solvents using bacteria. He found one, Clostridium acetobutylicum, that eats carbohydrate and produces a mix of three chemicals: acetone, butanol and ethanol. The method became known as ABE fermentation, or the Weizmann process. Chemistry World describes how the Weizmann process changed everything by relying on that organism to ferment cereals.

At first it was a lab curiosity. Asked how much acetone he could make, Weizmann is quoted as replying, “So far, I have succeeded in making a few hundred cubic centimetres of acetone at a time by the fermentation process.”

Demand for cordite pushed it much further, fast. By 1917, according to the same Chemistry World account, the process was making almost 3,000 tons of acetone a year at the Royal Navy Cordite Factory at Holton Heath in Dorset.

Getting there meant solving a problem no one had cracked at that scale. A fermentation this large had to be kept free of other microbes, or the whole batch would spoil. The Microbiology Society’s magazine, The Microbiologist, describes it as “the first microbiological process to require asepsis on an industrial scale.” After the war it kept running commercially for decades, until cheaper oil-based methods pushed it out.

The whisky problem: most of it is not whisky

Jump a century forward and a few hundred miles north.

Making Scotch malt whisky is, in pure material terms, mostly a business of producing things that are not whisky. By one estimate, as little as 7 percent of what comes out of the distillery is the drinkable spirit. Everything else is left behind.

Two leftovers dominate. There is pot ale, the liquid from the copper stills, and draff, the spent grains. Pot ale carries traces of copper picked up from those stills. Across the whole industry the volumes are large. Scotland’s malt whisky sector produces almost 750,000 tonnes of draff and two billion litres of pot ale a year. Some of it becomes animal feed and fertiliser. A lot of it is simply a cost to get rid of.

Old process, new feedstock

This is where the two eras meet. Celtic Renewables, an Edinburgh firm founded in 2012 as a spin-out from Edinburgh Napier University by the microbiologist Professor Martin Tangney, took that century-old fermentation and pointed it at whisky waste. Draff and pot ale are rich in carbohydrate, which is exactly what the bacterium wants to eat. What the company is after is biobutanol, a direct petrol substitute that goes straight into an ordinary engine.

In 2017 they tested the idea in the real world, filling up a Ford Focus and driving it. Tangney called it the first time in history a car had been driven on a fuel made from whisky waste. He was honest that this was a proof of concept, not a filling station. He told Saveur, “We physically poured a bottle of [alcohol] butanol into the car, but the scale of this could be huge.”

The pitch behind the company is less about whisky than about waste economics. Tangney says his objective is “to change the economy, taking stuff with limited use and upvaluing it.” The firm has since built what it describes as Scotland’s first biorefinery, at Grangemouth.

Then versus now: what changed, and what didn’t

The microbiology is essentially the same in both eras. Same type of bacterium, same three-chemical output, same need for a clean ferment that made the 1916 job so hard. What changed is everything around it.

In the war, the product that mattered was acetone. Butanol was close to a nuisance, piling up in storage. Today the value has flipped: butanol is the target, as a fuel, and the process is run for the very molecule the original operators barely knew what to do with.

The pressure has flipped too. A hundred years ago it was a shortage, a cut-off supply chain. Now it is the opposite, a surplus. An industry is making residues faster than it can usefully use them.

The raw material is the sharpest contrast of all. Weizmann’s plants ran on grain, and later lost out to cheap oil-based chemicals. Celtic Renewables runs on material that already exists whether anyone ferments it or not, and would otherwise cost money to throw away.

What strikes us here is how little of this is invention in the usual sense. The chemistry was worked out over a century ago, scaled up, then retired when oil got cheap. Nothing about the bacterium changed. What changed was the economics around it: a waste stream big enough and troublesome enough to make an old, shelved process look efficient again. A technology can be abandoned not because it stopped working but because the world around it moved on, and it can come back for the same reason. The whisky residues were always going to be produced. It took a First World War solvent recipe to make them worth something.