Draff and Pot Ale: What Happens to the Leftovers

Draff and pot ale are whisky production’s grain and liquid leftovers, but they can become animal feed, recovered protein, heat, biogas or chemicals. The useful distinction is between finding another use for these materials and proving an environmental benefit: a reuse claim, a plant’s output and a carbon saving are different things.

What are draff and pot ale?

Draff is spent grain. Glenfiddich describes pot ale as “the residue from fermented mash liquid”, while The Chemical Engineer calls it the “copper-containing yeasty liquid” left after distillation. These are different materials, with different handling requirements and possible destinations.[9][3]

Their water content helps explain the distinction. Zero Waste Scotland’s sector study gives draff a dry matter content of 23%, compared with 6% for pot ale and under 4% for spent lees and washwater, another liquid by-product stream. A tonne of each therefore does not represent the same quantity of dry material.[1]

Calling everything “waste” can obscure those differences. Zero Waste Scotland describes distillery by-products as an abundant source of proteins and carbohydrates, although its study also records substantial disposal of liquid material.[1]

How much material is there?

The published totals are Disputed, rather than a single settled industry figure. For Scotland, Zero Waste Scotland’s 2015 sector study estimates 684,000 tonnes of draff, 2,016,000 tonnes of pot ale and 361,000 tonnes of spent lees and wash a year.[1]

Edinburgh Napier University’s 2017 account gives almost 750,000 tonnes of draff and 2 billion litres of pot ale from the malt whisky industry. The trade publication scotchwhisky.com gives 500,000 tonnes and 1.6 billion litres respectively. Those figures should remain attributed, not be combined into a new total.[2][11]

The units matter as much as the disagreement: tonnes and litres are not interchangeable measurements. Nor should figures published in different accounts be presented as a current annual total.

Zero Waste Scotland also lists 32,000 tonnes of pot ale syrup and 254,000 tonnes of distillers dark grains. These are processed products, so they should not simply be added to the raw by-product figures as though every entry represented a separate original stream.[1]

Animal feed: an established destination

Feeding livestock is one of the established uses for distillery leftovers. scotchwhisky.com describes draff being pelleted and supplied to farmers as cattle feed, while Zero Waste Scotland’s 2015 estimate records all 684,000 tonnes of draff going to animal feed.[11][1]

Rothes in Speyside provides an example of processing draff and pot ale together. According to equipment supplier Siltbuster’s account, the site has made Distillers Dark Grains feed from these materials since 1970. That is a processed feed destination for both the grain and liquid streams, rather than a use for draff alone.[7]

The practice extends beyond Scotch whisky. In its Sustainable Together roadmap, published in 2022, the Irish Whiskey Association reports that over 350,000 tonnes of spent grain and pot ale from Irish whiskey production are reused annually as animal feed. The association is an industry body, and this is its reported figure.[12]

Its target is to reuse 100% of spent grain and pot ale, eliminating organic waste. That target is separate from the reported tonnage already reused: the roadmap’s ambition should not be rewritten as an achieved industry-wide result.[12]

This is one reason the broader sustainability guide needs to distinguish established practices from new projects and future commitments.

Recovering protein from pot ale

Pot ale can also be a source of protein for fish feed. Heriot-Watt University describes Horizon Proteins, a spinout registered in 2014, extracting protein from pot ale and identifies Scottish salmon farming as an initial key market.[8]

The university describes a plant venture with Rothes CoRDe and an agreement for EWOS Cargill to take the initial protein output. Its stated initial processing capacity was planned at 200,000 tonnes of pot ale a year, yielding about 2,500 tonnes of protein, with expansion envisaged to 1 million tonnes and 12,000 tonnes respectively.[8]

Those are planned capacities, not achieved production figures. The useful point is the proposed separation of a feed ingredient from pot ale, rather than an assumption that the entire liquid stream becomes protein.

The opportunity is substantial in the historical assessment: Zero Waste Scotland estimated that pot ale disposed of to sea and rivers contained 69,552 tonnes of protein. That estimate belongs to its sector study, not to a measurement of present-day losses.[1]

Making heat and biogas

Energy recovery takes more than one form. At Rothes CoRDe, draff is used in biomass combined heat and power, while the Glendullan and Glenfiddich examples use anaerobic digestion to produce energy or biogas from residues.[6][11][9]

According to supplier AET Biomass, the Rothes plant uses 115,000 tonnes of wet draff and 60,000 tonnes of clean wood annually, with an electrical generating capacity of 7.2 MWe. It also supplies about 12 tonnes of steam an hour to a pot ale syrup plant.[6]

Those figures describe a combined draff and wood operation, not electricity generated from whisky leftovers alone. The plant operator claims an annual saving of 64,000 tonnes of carbon dioxide; independent verification is not reliably established.[6]

Glendullan’s anaerobic digestion plant opened in 2015. In its first 12 months, it generated 6,000 MWh of thermal energy and reduced fossil fuel demand by 25%, according to scotchwhisky.com. These are first year results, not a statement of current annual performance.[11]

Glenfiddich says it turns draff and pot ale into biogas and claims to be the first distillery to process 100% of its residues on its own site. Transport Engineer reports that leftover digestate solids fertilise barley fields belonging to farmers supplying the distillery.[9][10]

Biogas does not mean zero emissions. Glenfiddich claims carbon dioxide reductions of over 95% against diesel, while IVECO specialist Jorge Asensio Lopez says biomethane cannot be classed as zero emission. Both statements can be true: a reduction is not the same as zero emissions.[9][10]

The distinction also matters when reading about energy in whisky production.

Turning residues into chemicals

Celtic Renewables uses acetone butanol ethanol fermentation, usually shortened to ABE, with draff and pot ale. The Chemical Engineer reports that the process produces acetone, butanol and ethanol in a ratio of 3:6:1.[3]

The company’s Grangemouth project has evidence beyond a development announcement. SEPA records issuing permit PPC/A/1193001 to Celtic Renewables Grangemouth Plc for the Caledon Green plant on 29 January 2022. A permit establishes that regulatory event, not the plant’s production volume.[5]

Celtic Renewables says construction finished at the end of 2022, operations began in 2023, and its first tanker of bioacetone and biobutanol departed on 19 November 2024. It also claims “up to a 65% carbon saving in comparison to petrochemicals”. The operating chronology and carbon comparison are the producer’s account.[4]

This route makes chemicals rather than animal feed or heat. It should therefore be described by its actual outputs, not folded into a general claim that all whisky residues become fuel.

What still needs treatment?

Not every destination is a recovered product. Zero Waste Scotland’s 2015 study records over 2 million tonnes of draff, pot ale and spent lees disposed of to sea or land, alongside the 684,000 tonnes used as animal feed.[1]

Pot ale is not harmless water. The trade accounts identify copper in the liquid and describe treatment of pot ale and spent lees to remove toxic copper levels before release into large, fast-flowing water bodies.[3][11]

At Rothes, Siltbuster describes an effluent plant treating waste from nine distilleries before licensed discharge to the River Spey. This is a documented treatment arrangement at that site, not a description of every distillery’s practice.[7]

Location also affects the opportunity for reuse. In its 2015 sector study, Zero Waste Scotland reported that remote coastal and island distilleries recovered useful products from only a small proportion of their by-products. A successful shared processing site should not be assumed to represent every setting.[1]

How to read a leftovers claim

Use this checklist when a distillery or processor announces a new use:

1. Identify the material: draff, pot ale, spent lees or a processed product.
2. Identify the result: feed supplied, protein extracted, energy generated or chemicals shipped.
3. Check the measurement: tonnes processed, generating capacity and energy output describe different things.
4. Separate stages: a target, permit, planned capacity and reported output are not equivalent.
5. Keep attribution: a company’s carbon saving remains its claim unless independently established.

These distinctions prevent a promising project becoming a broader claim than its evidence supports. They are also useful when assessing packaging and greenwashing, where a measurable improvement and a general environmental claim are not the same thing.

Where to go next

• Sustainability in Whisky: The Complete Guide: place by-product reuse within the wider production picture.
• Energy in Whisky Production: Fuels, Heat and Renewables: distinguish energy sources, recovered heat and reported reductions.
• Water Use in Distilling: explore the related questions around water and liquid streams.

Sources

1. Zero Waste Scotland, Ricardo Energy & Environment. Biorefining Potential for Scotland. Edition undated in the supplied record; 2015 sector estimates. https://cdn.zerowastescotland.org.uk/managed-downloads/mf-hg3ozjia-1681982787d
2. Edinburgh Napier University. Celtic Renewables to build whisky residue biofuel plant at Grangemouth. 2017. https://www.napier.ac.uk/about-us/news/celtic-renewables-to-build-whisky-residue-biofuel-plant-at-grangemouth
3. The Chemical Engineer. Roadtrip fuelled on whisky waste. 2017. https://www.thechemicalengineer.com/news/roadtrip-fuelled-on-whisky-waste/
4. Celtic Renewables. First Tanker Shipment of Green Chemicals From Scotland's Biorefinery. 2024, producer’s account. https://www.celtic-renewables.com/first-tanker-shipment-of-bioacetone-biobutanol/
5. Scottish Environment Protection Agency. Celtic Renewables Grangemouth Plc: Caledon Green Exemplar Plant. Permit issued 29 January 2022. https://consultation.sepa.org.uk/permits/caledon_green_exemplar_plant_ppc_application/
6. AET Biomass. Rothes CoRDe, Speyside, UK. Undated, supplier’s account. https://www.aet-biomass.com/en-gb/home/references/biomass-fired-plants/rothes-corde-speyside.aspx
7. Siltbuster. Rothes CoRDe Ltd Distillery Effluent. Undated, supplier’s account. https://www.siltbuster.co.uk/case-studies/rothes-corde-ltd-distillery-effluent/
8. Heriot-Watt University Research Portal. Horizon Proteins: Circular Economy Innovation from Whisky By-products. Undated institutional account. https://researchportal.hw.ac.uk/en/impacts/horizon-proteins-circular-economy-innovation-from-whisky-by-produ/
9. Glenfiddich. Glenfiddich fuels transport fleet with breakthrough green biogas made from its own whisky residues. Undated, producer’s account. https://www.glenfiddich.com/general/sustainability-press-release/
10. Transport Engineer. Off-grid gas. Undated trade account. https://www.transportengineer.org.uk/content/features/off-grid-gas/
11. scotchwhisky.com. Putting whisky waste to good use. Undated in the supplied record, trade account. https://scotchwhisky.com/magazine/features/13263/putting-whisky-waste-to-good-use/
12. Drinks Ireland, Irish Whiskey Association. Sustainable Together: Sustainability Roadmap 2022. 2022. https://www.ibec.ie/drinksireland/-/media/documents/drinks-ireland-new-website/irish-whiskey/iwa-sustainability-roadmap-2022.pdf

This desk-researched article uses the site’s verified fact sheet, distinguishing historical estimates, institutional and trade reporting, producer claims and planned capacity.

Last checked: November 2026