A landmark piece of research published this month out of one of the world's most respected institutions for distilling science has quietly landed in the technical literature — and its implications stretch far beyond Scotland's misty glens. Researchers at Heriot-Watt University in Edinburgh have identified a surprisingly straightforward modification to the fermentation stage of Scotch malt whisky production that, if adopted at scale, could slash energy use and carbon emissions by as much as 16 percent for every liter of pure alcohol produced. The finding puts a spotlight on a part of the production process that seldom gets the same attention as barrel selection or distillation cuts, and raises a question that producers on both sides of the Atlantic will soon need to answer: how much efficiency are they leaving on the table before the spirit even reaches a still?
The Science of Wash Strength: What the Heriot-Watt Study Actually Found
To understand the significance of the research, it helps to understand where wash fits inside the broader arc of whisky-making. The wash is the liquid created after the fermentation of a sweet cereal-based liquid known as wort, produced when yeast is added to cooled wort and converts the sugars into alcohol, resulting in a beer-like liquid. It is the foundation everything else is built on — and for generations, distillers have treated its strength as a largely fixed variable.
Researchers at Heriot-Watt University found that producing a stronger alcoholic liquid before distillation could make Scotch malt whisky production more efficient by cutting energy use, carbon emissions, and volume of liquid residues. That is not an incremental improvement. In an industry dealing with enormous throughput volumes, shaving 16 percent off energy consumption per unit of pure alcohol would represent one of the most meaningful efficiency gains achieved through process engineering in decades.
The Study's Methodology
The study, led by Dr. Shiwen Zhuang from the University's International Centre for Brewing and Distilling, is the first to measure how increasing wash strength from the industry standard of around 8% alcohol by volume (ABV) to between 10% and 14% ABV could affect the efficiency and environmental impact of Scotch malt whisky production. The fact that this is described as a first is itself telling. Despite centuries of whisky-making tradition and decades of applied food science, no one had apparently run the full model before — at least not in a way that could be published and peer-reviewed against real-world fermentation benchmarks.
Using a model that reflects real-world fermentation and traditional two-pot distillation, the researchers found that increasing wash strength to 14% ABV could reduce energy use and carbon emissions by around 16% for every liter of pure alcohol produced. That modeling framework is important. The team was not working with theoretical best-case assumptions; the numbers are anchored to the conditions that actually exist inside a working distillery.
The research was published in the Journal of the Institute of Brewing and was carried out by Dr. Zhuang, Dr. Jane White, and Professor Chris Boulton. The Journal of the Institute of Brewing is among the most rigorous peer-reviewed publications in the field, so the findings carry the weight of serious scientific scrutiny rather than industry-funded promotional research.
What Happens to the Waste Streams
The emissions reduction figure grabs the headlines, but the study's data on liquid residues may end up being equally important to the economics of adoption. This approach could also cut pot ale volumes — the nutrient-rich liquid remaining after the first distillation — by 55%, and reduce spent lees, the liquid remaining after the second distillation, by more than 30%, significantly lowering liquid residues from the distillation process.
Those are not minor footnotes. Pot ale and spent lees are the two most voluminous byproducts of traditional pot still production, and managing them is a persistent operational headache across the industry. A stronger wash means more alcohol enters the still with less water, so less liquid needs to be heated and processed to produce the same amount of spirit, and lower residue volumes could also reduce handling, transport, and treatment needs at distilleries. A 55-percent reduction in pot ale volume is the kind of number that causes operations managers to sit up straight — because pot ale treatment, haulage to processing facilities, and its conversion into animal feed or fertilizer all carry hard costs that add up across thousands of production runs per year.
Why Distillation Is So Energy-Hungry — and Why Fermentation Is the Upstream Lever
Distillation is one of the most energy-intensive stages of spirits production. Every distillery that runs copper pot stills knows the fuel costs intimately — gas or steam must continuously heat enormous volumes of wash-filled copper vessels, often for hours at a stretch, to coax alcohol vapor up and over the lyne arm and into the condenser. The less water that goes into the still alongside the alcohol, the less energy is wasted heating something that ultimately gets thrown away.
Traditional distillation methods require significant energy, contributing to the sector's carbon footprint, while fermentation and distillation generate large amounts of heat and cooling systems require excessive water use, further straining natural resources. This is the structural problem that the Heriot-Watt team is trying to chip away at — not by redesigning copper stills or switching fuel sources, but by asking whether distilleries are sending too much water into the still in the first place.
The logic is elegant in its simplicity. If the industry standard wash comes in at roughly 8% ABV, then for every liter of alcohol entering the still, there are approximately eleven and a half liters of water tagging along for the ride — water that must be heated, vaporized to varying degrees, and then handled as pot ale or spent lees on the back end. Pushing that wash to 14% ABV fundamentally changes the ratio. More alcohol, less water, less energy per unit of output. The thermodynamics are straightforward; the challenge is the chemistry and the craft.
The Obstacles: Yeast, Flavor, and the Mashing Problem
The research team is transparent about the fact that stronger fermentation is not simply a dial that distillers can turn up without consequence. The authors acknowledge that there are challenges to adopting this approach more widely because producing higher levels of fermentable sugars may require new approaches to mashing, while the effects on yeast performance, flavor development, and the wider production process need further study.
The mashing challenge is real and non-trivial. To arrive at a 14% ABV wash, you need substantially more fermentable sugars in your wort to begin with. That means either increasing the concentration of malt per unit of water during mashing — which can create viscosity problems and affect extract efficiency — or finding new enzymatic or process-engineering solutions to push more sugars into solution. Neither path is impossible, but both require investment in process development that goes well beyond simply telling fermentation operators to aim higher.
Yeast performance at higher sugar concentrations is a more delicate issue still, particularly when flavor is considered. Distilling yeast strains are selected not just for their ability to convert sugars to alcohol efficiently, but for the congener profiles they produce along the way. A process change that increases alcohol yield before energy-heavy downstream steps could become a useful route for lowering operating costs and environmental impact, but only if product quality holds up in commercial conditions. That last clause is the one every master distiller will be watching closely. A 16% emissions reduction means nothing if the character of the spirit changes in ways that customers — or whisky aficionados — can detect in the glass.
There is historical precedent for this concern. Grain whisky producers have operated at much higher fermentation strengths than malt producers for decades, but grain whisky uses continuous column stills rather than pot stills, and the flavor profile expectations are entirely different. Applying similar logic to single malt production is a genuinely new frontier, and the yeast physiology at those higher sugar concentrations — including elevated osmotic stress and potential shifts in ester and fusel alcohol production — remains an active area of investigation.
Economic Upside: More Than Just Cutting the Energy Bill
Dr. Jane White, one of the study's co-authors, pointed to dimensions of the findings that go beyond environmental accounting. White noted that the study also identified potential economic benefits, with lower volumes of pot ale and spent lees potentially reducing handling, transport, and treatment costs, while maintaining the concentration of valuable materials that could be recovered and reused from these residues.
That last point about maintaining the concentration of valuable materials is worth unpacking. Pot ale is not simply a waste product; it contains proteins, amino acids, and other organic compounds that have commercial value when processed into pot ale syrup for animal feed. If you reduce the volume of pot ale while keeping the concentration of those valuable compounds intact — or even increasing it — you have a more potent feedstock that can be processed more efficiently and sold at higher value per unit. The economics of distillery byproduct streams are more complex than most outsiders appreciate, and stronger wash could reshape those calculations in producers' favor.
The production capacity implications are potentially significant as well. Dr. Zhuang noted that these benefits could be achieved in different ways: existing distilleries may be able to increase output without expanding fermentation capacity, while new or growing distilleries could produce the same amount of whisky using smaller equipment and lower processing volumes. For an industry that has been on an extended capital expenditure cycle — dozens of Scottish distilleries have expanded or been built from scratch over the past fifteen years — the ability to get more production out of existing fermentation infrastructure without adding more washbacks is a meaningful operational lever.
The Net-Zero Context: Where This Research Sits in the Industry's Sustainability Race
The study arrives as the Scotch whisky industry is working toward net-zero targets and looking for ways to improve plant efficiency without cutting production. That framing captures the essential tension. Spirits producers face pressure from regulators, investors, and environmentally conscious consumers to reduce their carbon footprint, but no one is suggesting they should simply make less whisky. The only path forward is making the same amount — or more — with fewer emissions per bottle. That is exactly the kind of improvement the Heriot-Watt team is pointing toward.
The Scotch whisky industry is committed to cutting carbon emissions to net zero by 2040. Achieving that in roughly fourteen years while maintaining or growing production volumes requires stacking multiple efficiency gains on top of each other. Stronger wash fermentation, if it can be validated at commercial scale and across different malt profiles and yeast strains, becomes one brick in that wall — a process-level change that could contribute meaningfully to sector-wide decarbonization without requiring the wholesale replacement of aging copper pot still infrastructure.
Carbon capture technology is being implemented to trap and repurpose CO₂ emissions from distillation, heat recovery systems are enabling distilleries to reuse energy that would otherwise be lost, and renewable energy sources such as wind, solar, and biomass are increasingly being integrated into whisky production to reduce reliance on fossil fuels. The Heriot-Watt research adds a new tool to that toolkit — one that, unlike renewable energy infrastructure or carbon capture systems, operates entirely within the existing biological and chemical process of fermentation itself. No new machinery necessarily required; just a shift in how the wort is managed before the yeast goes in.
Prior research from the same institution adds context about just how complex the carbon accounting in this industry actually is. A simulated case study using a carbon footprint calculator for single malt Scotch whisky production calculated a carbon footprint of 2.83 kg CO₂e per 70 cL bottle of whisky, with Scope 1, 2, and 3 emissions accounting for 15%, 8%, and 77% of the total respectively. The dominance of Scope 3 emissions — those generated across the supply chain, including agriculture, packaging, and distribution — illustrates why tackling Scope 1 process emissions through fermentation efficiency improvements matters so much. Distilleries have the most direct control over their on-site production process, and that is precisely where stronger wash intervention would have its effect.
What Comes Next: A PhD Project and the Road to Commercial Validation
Heriot-Watt said it is now starting a new PhD project to build on the findings, a signal that the university views this line of research as having legs beyond a single modeling paper. PhD-level follow-on work typically means experimental validation — moving from modeled projections to actual fermentation trials, measuring not just the energy and residue outcomes but the flavor chemistry that would need to pass muster with the industry's most exacting palates.
These findings support the Scotch whisky industry's pursuit of net zero targets and efforts to improve efficiency while maintaining production. That phrase — maintaining production — is the governing constraint. The research will ultimately be judged not by what it does to an emissions spreadsheet, but by whether the whisky that comes out the other end still tastes like the whisky consumers and connoisseurs have come to expect. The flavor-neutral ceiling for wash strength manipulation in traditional pot still production is the central question that future work will need to answer.
Implications for American Bourbon and Whiskey Producers
American distillers — whether running Kentucky bourbon operations, craft rye programs in New York, or single malt projects scattered from Colorado to Washington state — have good reason to watch this research closely, even though it was designed specifically around Scotch malt whisky production and the two-pot still system. The underlying physics and chemistry of fermentation efficiency are not Scottish-specific. Bourbon distillers already operate in a world of varying distiller's beer strengths, yeast strain management, and byproduct stream optimization, and many of the same environmental pressures facing Scotch producers are bearing down on American ones too.
The bourbon industry has its own version of pot ale and spent lees in the form of stillage — the liquid left after distillation, often returned to grain as thin stillage or processed into distiller's dried grains with solubles (DDGS) for livestock feed. If higher-strength fermentation could reduce stillage volumes proportionally in a bourbon context, the operational savings could be substantial. Large-scale Kentucky operations run continuous column stills rather than copper pot stills, which changes some of the math, but the principle of reducing the water load entering the still before distillation remains relevant regardless of still type.
American craft distillers, for whom energy costs per unit of output are often far higher than for their large industrial counterparts, may find the proposition particularly compelling. A 16% reduction in energy use per liter of pure alcohol produced could represent a material improvement in operating margins for a small distillery running three or four fermenters and a single pot still. The challenge, as in Scotland, would be managing yeast performance and flavor consistency at higher wash or beer strengths — problems that are solvable with the right strain selection and process controls, but that require careful development work before any producer puts the results in a bottle with their name on it.
The Broader Picture: Process Innovation as the New Frontier in Spirits Science
What makes this research noteworthy beyond its specific numbers is what it represents about where the leading edge of distilling science is heading. For most of the past century, innovation in whisky production focused on the downstream end — new still designs, different cask types, novel maturation conditions, and creative blending techniques. The fermentation stage was treated almost as a black box: get the yeast in, get the wash out, move on.
The Heriot-Watt study is part of a growing body of work that treats fermentation as a dynamic, optimizable system with enormous untapped potential — not just for emissions reduction, but for flavor chemistry, production efficiency, and cost management simultaneously. As energy prices remain elevated and sustainability commitments become harder to ignore, the economic incentive to invest in fermentation science is greater than it has ever been.
The whisky industry has always been defined by patience — the willingness to wait years or decades for a product to reach its potential. Applying that same patience to process science, running the long-form experiments needed to understand what stronger wash really does to spirit character across different malt varieties, fermentation temperatures, and yeast strains, may ultimately prove to be as valuable an investment as any new warehouse full of aging barrels. The Heriot-Watt team has opened a door. The industry, on both sides of the Atlantic, will now have to decide how far it wants to walk through it.
