Whisky pot stills

Turning whisky distillery by-products into value-added opportunities

13th December 2018

This case study explores the potential to add value to unavoidable whisky distillery by-products via a process called ‘valorisation’.

Key Facts
Penderyn’s effluent is currently mixed and tankered away for land-spreading at a high annual cost
The added-value opportunities identified through WRAP Cymru support will potentially reduce effluent costs by 75%, provide a low-cost source of heat energy for the entire site and deliver a pot ale concentrate worth £10,000 per annum


This case study demonstrates how Penderyn Whisky Distillery (‘Penderyn’), with support from WRAP Cymru, has identified opportunities to transform its unavoidable, costly by-products into a valuable resource.  

Penderyn uses malted barley for its whisky production. As is typical, the waste products from its process include a malt draff, pot ale, spent lees and caustic wash from cleaning the equipment. Currently, the draff is sold into animal feed; however, Penderyn incurs a high annual cost to send the liquid pot ale, lees and wash by-products for land-spreading. 

WRAP Cymru worked closely with Penderyn through a two-staged approach. The first stage provided support to identify and appraise alternative, added-value markets for the draff and spent wash by-products. The second stage helped Penderyn to focus in on two key business opportunities; researching the capital and revenue costs associated with the installation of new plant machinery, together with cost-saving and revenue generation options.


This case study explores the potential to add value to unavoidable whisky distillery by-products via a process called ‘valorisation’. 

Penderyn Whisky Distillery is situated in the community of Penderyn in the Welsh Beacons. The main distillery, offices and visitor centre are in Penderyn, which operates two Faraday stills and two lantern stills. Penderyn produces its own malted barley spirit, which when matured is recognised as one of the finest single malt whiskies in the world. 

The majority of the spirit goes into casks for ageing in their warehouses, while the remainder is used to craft other award-winning alcoholic products, including Merlyn Cream Liqueur. It produces around 400,000 litres of pure alcohol annually, which is then used to produce Penderyn’s range of products.

Waste issues

Penderyn uses malted barley for its whisky production. The by-product, after the malted barley has been steeped in hot water and the soluble sugars extracted, is called draff. The malt draff is rich in digestible fibre, contains concentrated protein and oil and has a high moisture content of approx. 80%. The sugar-rich liquid, called wort, is fermented and then distilled.

Approximately 1,080 tonnes of Penderyn’s draff is collected by a local cattle farmer each year and used to support the feeding of his stock. There is no charge for the collection.

Penderyn's spent wash is made up of pot ale, spent lees and caustic wash from washing the stills and flushing the lines between production runs. The liquid effluent is combined and collected by a licenced contractor before being spread to land. This amounts to over 1.5 million litres a year. 

Penderyn sought support from WRAP Cymru to investigate ways to reduce its by-product management costs, and potentially develop added-value opportunities from these streams. 

Options appraisal

Initial options appraisal

WRAP Cymru provided a first stage of assistance to Penderyn to research and explore opportunities for adding value to the draff pot ale and the spent lees by-products. The emphasis of this investigation was to identify solutions that would work well practically for a distillery which has limitations on space.  

A range of potential options were explored by WRAP Cymru, including innovative pre-commercial systems and technologies for adding value to the pot ale and spent lees. This information was summarised and the options were scored according to three broad criteria: 

  1. The readiness of the technology required to deliver added value.
  2. The commercial potential of the value-added product.
  3. The ability to implement the opportunity practically on site. 

Options identified

The options appraisal identified 13 potential opportunities, some of which inter-linked in terms of treating both the liquid by-products and the draff.

The scoring and ranking process provided a structure through which Penderyn could focus on the most promising opportunities. The detail behind each option was summarised in a slide deck to enable the operations team at Penderyn to present the information easily to their board. 

After detailed discussions with both WRAP Cymru and the board, Penderyn decided to focus on three activities: 

  1. Initial separation of the liquid by-products (i.e. pot ale and lees from the wash).
  2. Technology for separating suspended solids and liquid solubles from spent grains during production.
  3. Brathadair’s pot ale treatment process for SME distilleries.   

WRAP Cymru then supported Penderyn to develop comprehensive business cases for the implementation of these opportunities.

Separation of pot ale and lees from caustic wash

A critical first step for Penderyn is the initial separation at source of the pot ale (at the wash distillation stage) and the spent lees (at the spirit distillation stage), leaving the remaining wash to be managed as trade effluent. 

The separation process will enable Penderyn to further treat and process the pot ale and lees to extract value from these by-products rather than dealing with them as an expensive waste stream. As a result, Penderyn intends to adapt its process to put in place separate tank storage to more effectively manage these streams. 

Separation of suspended solids from liquids

There is the opportunity for Penderyn to install a liquid/solid separator system to the distillery process, which will continuously remove a high proportion of the suspended solids from the pot ale, lees and wash waters. The outcome will increase the quantity of solids in draff form that can be sent to animal feed. It will also simultaneously reduce the solid content of the effluent waste waters, which is currently estimated at 5%. This will make the waste water more cost-effective to treat as trade effluent.

A 2-3m3/hr minimum flow rate is required to justify investment in the separation system. Maximum capacity will vary, but it can comfortably handle up to 50m3/hr. The return on investment on this system for Penderyn will be around 18 months. 

Pot ale/lees treatment

The treatment of pot ale   has long been problematic in the whisky sector. This is due to the fact it is produced in copious quantities, has a high polluting load and is acidic, with a typical pH value of around 3.5 – 4.0. 

According to research undertaken by the bioeconomy consultants, NNFCC, in 2017, 60% of Scottish SME distillers did not deploy technology in the treatment of their waste and were content either to have it spread to land as low-grade fertiliser or, where appropriately located, dumped to sea.  

Some whisky distilleries have invested in technology to convert the pot ale into a syrup, which can be sold as an animal feed additive, or mixed with draff to create a feed product called ‘distiller’s dark grains’. This is an energy-intensive process as it requires removal of over 90% of the water content.

Penderyn is instead exploring the potential to create a similar product from pot ale for the anaerobic digestion (AD) market. This will be in the form of a concentrate with 20% water content. This is specifically suited to AD facilities as a free-flowing concentrate is much easier to handle and manage than pot ale syrup. As the concentrate requires the removal of 80% rather than 90% of the moisture, it is a less energy-intensive process.

The Brathadair process

There is the opportunity for Penderyn to convert both the pot ale and the spent lees into a concentrate for the AD market using an innovative system developed by a company called Brathadair. The Brathadair process offers the opportunity for SMEs, such as Penderyn, to implement their system without large upfront capital investment costs.

The Brathadair system treats the pot ale and spent lees following the initial solid-liquid separation. The liquid by-product is highly acidic and, therefore, pH balancing is employed as a first stage. This results in precipitation of copper, as a particulate, for which cost-neutral markets can be found. The remaining effluent is then treated by evaporation leaving the free-flowing concentrate at around 20% of the original volume. This can then be sold into local AD facilities at around £25/tonne. 

Brathadair employs this technology alongside a water-source heat pump for cost-effective and efficient treatment of pot ale. The water-source heat pump is reliant on close proximity to a river which has a sufficiently high flow rate. 

Given the low cost of the energy, it will also be economic to process the spent lees in the same way. The energy required for evaporation will typically consume 50% of the power generated by the water-source heat pump. The remaining 50% can be used to power the other elements of the process that have an inherent heat demand.

Benefits to Penderyn

For a company the size of Penderyn, a cap-ex of £1million would be required to implement this type of system. Brathadair’s business model involves a special purpose vehicle (SPV) being established which will contract with Penderyn over a minimum 10-year period. The SPV will undertake the whole project. With backing from investment partners, it will purchase and install a water-source heat pump, evaporator and associated pipework and installation works at Penderyn's site. This approach will significantly lower the barrier to implementation that is normally presented by upfront capital expenditure. 

The SPV will capture the financial advantages from the Renewable Heat Incentive (RHI) and supply process heat from the water-source heat pump to Penderyn at low cost compared to their existing gas and electricity. Penderyn will therefore benefit from a reduction in overall energy costs associated with the process. 

Furthermore, the process will significantly reduce Penderyn’s existing effluent disposal costs, leaving just the caustic wash requiring disposal as trade effluent. Penderyn will also benefit from the income from the sale of the concentrate. 

In addition to benefiting from the extra income and significantly reduced operational costs, environmental impacts will also be much-reduced. 

For minimal initial investment and risk, Penderyn can maximise both economic and environmental opportunities.

Next steps

Penderyn is now in discussions with the technology providers to develop a more detailed business plan for potentially taking these opportunities forward. The initial liquid/solid segregation will be the easiest opportunity to implement rapidly. This will help prepare the ground for the more innovative and longer-term development around evaporating the pot ale and spent lees into a concentrate using renewable energy.