Distillery by-products, livestock feed and bio-energy use: report

We commissioned this report in response to concerns by livestock farmers about the impact of anaerobic digestion and bio-energy on the availability of distillery by-product for use as livestock feed in Scotland.

2. Distillery by-products output

Introduction to distillery by-products

3. There are two main types of Scotch whisky produced; malt whisky and grain whisky. Malt whisky is produced from malted barley while grain whisky is produced using grain (wheat or maize) and a small quantity (~10%) of malting barley.

4. A range of by-products are produced from the Scotch malt and grain distilling processes as outlined in the following table. These by-products have differing characteristics which determine their suitability for different end uses. The two predominant uses are; livestock feed and bio-energy production. Bio-energy production is principally achieved using Anaerobic Digestion but there are also a small number of Combined Heat and Power plants using draff as a feedstock in the combustion process.

5. Distillery by-product can be wet, liquid or pelletised. Some are utilised in their raw or minimally processed form straight out of the distillery; draff and grain moist feed. Other products undergo further processing. Distiller’s Dark Grains with Solubles are formed by combining, drying and pelletising in the case of malt whisky; draff and pot ale syrup and in the case of grain whisky; grain moist feed and spent wash syrup. Both pot ale and spent wash syrup are produced by concentrating the very dilute liquids from the malt and grain distilling processes respectively to form a thick syrup. Details of the typical processes involved in whisky production are detailed in Appendix 1. Bioethanol plants produce similar by-products. Actual processes vary widely from distillery to distillery.

Table 1. Summary of distillery feed by-products and use




Dry Matter (typical) (%)






Pot ale syrup








Grain moist feeds




Spent wash syrup




Wheat/Maize DDGS



Source: SRUC. Note - * Distiller’s Dark Grains with Solubles (DDGS)

Appendix 1 outlines the inputs, process flows and product outputs involved in malt and grain Scotch whisky production.

Estimated output of Scotch whisky distillery by-products

6. Estimates of total output of Scotch whisky distillery by-products were calculated for the period 2000 to 2017 based on available industry data. Projections were also made from 2017 to 2022.

7. These estimates were calculated using the following data:

  • Spirit production (in million of Litres of Pure Alcohol (m LPA) and spirit yields (LPA per tonne of malt and grain) (Gray, AS, 2017)[1] and based on the Scotch Whisky Association Databank.
  • Conversion factors in distilling from malt/grain to feed by-product obtained from industry experts Pass et al (2003)[2].
  • Full details of the calculations are given in Appendix 2 and results displayed in Figure 1.


8. Based on these methods the production of Scotch whisky distillery by products in Scotland in 2019 is estimated to be 443,000t of Dry Matter (DM) equivalent (Figure 1, Table 2 following). This comprises the total output (on a 100 % dry matter basis) of distilling by-products for both malt and grain distilling. In practice, as well as dried and pelletised product (at around 10% dry matter) much of this feed is produced in a wet form with dry matter in the 20% to 30% range for draff and substantially lower for other by-product streams such as pot ale. Therefore on a wet basis a much greater overall tonnage is produced.

9. The level of distillery by-product output mirrors changes in Scotch whisky production. The industry is estimated to have produced a record 531,000t DM of by-product in 2013. Output then fell 20% (109,000t DM) by 2017 to a low of 422,000t DM. Output has since started to rise and is expected to increase by 13% (56,000t DM) between the low of 2017 up until the forecasted values in 2022. This suggests that overall availability of distillery by-product will increase but it is not known in which sectors (livestock feed, bio-energy) this increased supply will be utilised.

10. Given the uncertainties outlined above these estimates should only be taken as a starting point for the potential availability of feed by-products from the distilling sector.

Figure 1: Estimated by-product feed output from Scotch whisky distilling

Figure 1: Estimated by-product feed output from Scotch whisky distilling

Source: SRUC

Table 2: Estimated by-product feed output from Scotch whisky distilling in Scotland

‘000’s t Dry Matter
2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022

Distillery by-products














Source: SRUC

UK production of bio-ethanol by-products

11. The output of bio-ethanol plants in England has been extremely variable, responding to volatile conditions in global grain and ethanol markets. In September 2018 the large Vivergo ethanol plant (1.1mt of grain, 0.35mt of by-product) on the Humber was closed (it is assumed permanently) due to lack of profitability. The estimates above assume continuation of production at the remaining Ensus ethanol plant on Teeside (1.0mt of wheat, 0.30mt of by-product). However, in October 2018 it was announced this plant would close for extended maintenance from December 2018 for an unknown period. In summary, the recent growth of UK bio-ethanol production has helped counter the fall in feed by-product availability from the Scotch whisky distilling sector (see Table 8). This has helped to maintain or increase overall UK supply of distillery by-products. However, the current lack of profitability in the ethanol market is leading to closure and extended maintenance of these bio-ethanol plants curtailing by-product output.

Scottish production of draff alternatives - brewery by-products

12. When considering distillery by-products as feed it is useful to consider the supply of alternative sources of similar feeds. Beer production results in output of a similar by-product to distillery draff with very similar feeding values known as brewer’s grains.

13. Beer production in Scotland was estimated at 2,435,000 hecto-litres (HL) in 2013 according to the Scottish Government[3] though this is an approximate value as no official estimates of beer production in Scotland are available. Total UK beer production has declined from 55 million HL in 2000 to 39 million HL in 2016 according to the British Beer and Pub Association. In the absence of production data for Scotland it is not known how beer production in Scotland may have changed in recent years.

14. Based on typical levels of by-product production per unit of beer produced, this is estimated to have resulted in the production of 48,700t of brewer’s grains in Scotland in 2013. At 23% dry matter this would equate to 11,201 t of dry matter. This was equivalent to 2% of the 529,000t DM of distillery by-products estimated to have been produced by the Scotch whisky industry in that year (2013). Therefore, while locally significant, the production of feed by-products from the brewing sector in Scotland is a relatively minor component of national feed supply.

Scottish production of malt feed by-products

15. Scotch whisky production is based on the use of malting barley. The malting process generates a range of by-products that can serve as feed for livestock or other sectors including bio-energy. The primary malting by-product is malt culms; the sprouted shoots of barley. Other by-products include malt corns, barley dust and malt dust. These by-products are usually blended with a binder and pelletised to produce a feed product known as malt residual pellets.

16. No official figures are available for the annual quantity of barley malted in Scotland nor the level of malt feed by-product generated. However, Scottish Government produce estimates of the quantity of Scottish barley used for human and industrial uses[4] which in 2017 was estimated to total 949,000 t. The Scottish Government do not give a breakdown of actual end uses within this category, but based on industry knowledge, SRUC understand that almost all of this is used for malting apart from a relatively small and undisclosed quantity for milling and pearl barley production.

17. The MAGB estimate[5] that the GB malting industry is capable of producing around 50,000t of feed by-products from a GB malting usage of approximately 2,000,000t of malting barley. Given likely malting barley use in Scotland of over 900,000t in 2017 this is expected to result in approximately 22,500t of malt feed by-products being produced in Scotland. At 90% dry matter this would equate to approximately 20,000 t of dry matter. This would be equivalent to around 5% of the 422,000t DM of distillery by-products estimated to have been produced by the Scotch whisky industry in that year (2017). Therefore, while locally significant, the production of feed by-products from the malting sector in Scotland is a relatively minor component of national feed supply.


Email: Gordon.Jackson@gov.scot

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