Scotland's whisky industry is famous for its single malts, but every dram comes with a less glamorous by-product: thousands of tonnes of draff (spent grain) and pot ale (a yeasty liquid residue). For decades, most of it went to cattle feed or was dumped at sea. Now, a cluster of startups and research institutes is eyeing this waste as a solution to one of the most pressing problems in European aquaculture: the overexploitation of wild fish stocks.
Farmed salmon, the continent's most consumed fish, still relies heavily on fishmeal and fish oil derived from wild-caught species such as anchovies and sand eels. Environmental groups have long warned that this practice is unsustainable, pushing marine ecosystems to their limits. The European Commission's own farm-to-fork strategy calls for a significant reduction in the use of wild fish in aquaculture by 2030.
From pot ale to protein
The idea is not entirely new. Farmers have fed draff to livestock for centuries. But turning it into a high-quality protein source for fish requires more than simple drying. Several Scottish companies are now using fermentation and microbial processes to convert the sugars and fibres in whisky waste into single-cell proteins, which can replace a portion of the fishmeal in salmon diets.
One such venture, based in the Speyside town of Rothes, has partnered with two local distilleries to collect their spent grains and pot ale. The facility, which opened earlier this year, uses a proprietary strain of yeast to produce a protein-rich biomass. Early trials at the University of Stirling's Institute of Aquaculture suggest that replacing 30% of the fishmeal with this protein has no adverse effect on salmon growth or health.
“We're not trying to eliminate fishmeal entirely,” said Dr. Fiona MacLeod, the project's lead researcher. “But if we can cut the wild-fish component by a third, that's a massive win for the oceans.”
The economics are also promising. Distilleries currently pay to dispose of their waste, so the startups can source their raw material at little or no cost. This makes the resulting protein competitive with imported fishmeal, which has seen price volatility due to climate-driven shifts in fish populations off the coasts of Peru and Chile.
A circular economy for the Highlands
The initiative fits neatly into the broader push for a circular economy in Europe. The European Union's Circular Economy Action Plan, part of the Green Deal, explicitly encourages the valorisation of organic waste streams. Scotland, though no longer an EU member, has its own circular economy strategy that aligns with these goals.
Local politicians have welcomed the development. Richard Lochhead, MSP for Moray, called it “a classic example of Scottish innovation turning an environmental problem into an economic opportunity.” The Scottish government has pledged £2 million to support further research into by-product valorisation.
Beyond Scotland, similar projects are emerging in other whisky-producing regions. In Ireland, the Dingle Distillery is experimenting with using its pot ale to grow microalgae, which can also serve as a fish feed ingredient. In France, researchers at the Université de Bretagne Occidentale are studying the use of cider and calvados waste for the same purpose.
Still, challenges remain. Scaling up from pilot to commercial production requires significant capital investment. The regulatory framework for novel feed ingredients in the EU is still evolving, and approval can take years. Moreover, the supply of whisky waste is finite—Scotland produces around 500,000 tonnes of draff and 1.6 billion litres of pot ale annually, but not all of it is suitable for processing.
Nevertheless, the potential is significant. If even a fraction of that waste is converted into fish feed, it could reduce the pressure on wild fish stocks while providing a new revenue stream for distilleries. For a region that has seen its traditional industries decline, this is a welcome twist.
As Dr. MacLeod put it: “Whisky has always been about patience and craft. Now it's also about sustainability.”
