Washbacks: Wooden vs Stainless Steel
A washback is the fermenting vat where yeast is added to wort, the liquid from mashing, to make wash, the fermented liquid. Wooden washbacks offer insulation and a home for resident micro-organisms; stainless steel offers surfaces that are easier to clean reliably, but neither material is established as producing better whisky in every distillery. [1][2][5]
What wooden and stainless steel washbacks do
The washback belongs between mashing and distillation. Its job is fermentation, not maturation, a distinction that matters when comparing a wooden vessel with a wooden cask. The Scotch Whisky Technical File describes wort being transferred to a washback and yeast being added there. [5]
For the preceding stage, see how mashing produces fermentable sugars. The separate guide to how wash is made explains fermentation itself; here, the question is what the vessel contributes.
Timber washbacks are traditionally made from pine or larch, according to ScotchWhisky.com’s technical account. Stainless steel provides a different working surface: where wood is porous and has crevices, steel is easier to clean reliably, particularly when the vessel has a conical base. [1]
Those differences give the comparison its useful starting point. Insulation, cleaning and resident microbial populations are documented considerations; a universal ranking of the resulting spirit is not established by the research recorded here. [1][2][3]
| Criterion | Wooden washbacks | Stainless steel washbacks |
|---|---|---|
| Surface | Porous, with crevices that complicate cleaning. [1] | Surfaces are easier to clean reliably. [1] |
| Heat insulation | Insulating properties are cited in trade reporting and Heriot-Watt research. [1][3] | The cited evidence does not provide a measured thermal comparison. [2][3] |
| Resident organisms | Distillery-associated organisms have been recovered from within washback wood. [3] | The cited wood study does not establish a corresponding result for steel. [3] |
| Comparative flavour evidence | Producer views and research proposals exist, but no measured wood-versus-steel flavour difference is established here. [1][2][7] | The same evidence limit applies. [1][2][7] |
The case for wooden washbacks
Insulation and temperature
Wood’s insulating properties are one reason wooden washbacks remain in Scotch malt production, according to Heriot-Watt research. Insulation is not an uncomplicated advantage, however: the trade account notes that high temperatures in a wooden washback can be difficult to bring down. [1][3]
Glenfiddich’s brand ambassador, Struan Grant Ralph, makes a stronger case for the distillery’s own practice. In a sponsored trade article published in 2023, he says wooden washbacks allow better temperature maintenance and that the new make spirit, the spirit before maturation, was better than that obtained from stainless steel. That is an attributed producer judgement, not an independent comparative trial. [7]
The distinction matters. The research supports insulation as a reason for using wood; Glenfiddich’s account adds a judgement about its own spirit. They are different kinds of evidence and should not be presented as interchangeable proof. [3][7]
Micro-organisms, rather than timber flavour
A wooden washback should not be understood as a miniature maturation cask. ScotchWhisky.com’s account says the wood itself does not flavour the wash; instead, micro-organisms surviving in it can contribute flavour congeners, meaning compounds associated with flavour. [1]
The peer-reviewed paper Experimental Whisky Fermentations: Influence of Wort Pretreatments likewise describes wooden washback microflora as contributing to flavour development. It also notes that microbial populations vary between batches with cleaning, raw materials and environmental factors. [4]
Wood therefore brings more than a choice of construction material. It can support a resident microbial community, but that community exists alongside other influences on fermentation. The presence of wood alone does not establish which compounds will result, or how a finished whisky will taste. [2][4]
The case for stainless steel washbacks
The clearest practical argument for stainless steel is cleaning. Wood’s pores and crevices make reliable cleaning more difficult, while stainless steel’s surface is easier to clean, especially with a conical base, according to the trade comparison. [1]
That is not a minor distinction. The same source describes poor cleaning as the most common cause of failed fermentation and notes that Lactobacillus bacteria compete with yeast for sugar in the wort. A microbial contribution to flavour and an unwanted fermentation problem are not simply two names for the same desirable effect. [1]
Nor does easier cleaning establish that steel produces less interesting spirit. Glenfarclas’s position, reported by ScotchWhisky.com, is that changing from wood to steel made “no difference at all”. That is the distillery’s assessment, just as Glenfiddich’s preference for wood is its own assessment. [1][7]
Steel’s strongest supported advantage in this comparison is therefore practical and specific: a surface that can be cleaned more reliably. It does not need an unsupported claim of superior flavour to make that a meaningful distinction. [1]
What the microbiology research actually shows
The most revealing evidence concerns what can live on and inside washback wood. A Heriot-Watt longitudinal study, described in a 2023 seminar synopsis, sampled the inside and outside of wooden washbacks, including a new vessel, during a silent season and again a year later during production. [3]
The exterior microbial community was consistent during production but shifted during the silent season. The researchers also examined wood from a decommissioned washback after six months of storage, recovering distillery-associated organisms from samples taken at depths of up to 12 mm. [3]
That finding supports persistence within the material. It does not, by itself, measure a flavour difference between otherwise comparable wooden and stainless steel fermentations, nor does the synopsis establish how any resulting difference would survive into mature whisky. [3]
A separate peer-reviewed study provides broader context. Its survey of 23 Scottish malt distilleries isolated 64 Lactobacillus strains; at one distillery, the bacterial range remained stable over 12 months, with malt supply and the annual maintenance closure influencing it. [9]
Together, these findings make the microbial question more interesting than “wood contains bacteria”. They show persistence and patterns of community change, while also pointing to influences beyond the vessel. For the organisms’ wider role, see lactic acid bacteria in whisky fermentation. [3][4][9]
Does wood change the whisky?
Story box: Wood, steel and producer views
Founding story: Not documented.
Turning point: In the 1960s, Glenfarclas gradually replaced wooden washbacks with steel, retaining wooden lids for heritage. Source
Documented record: Trade reporting records contrasting producer views about the effect of washback material. Source
Claim source mapping: The Glenfarclas changeover, retained lids and producer views are reported by ScotchWhisky.com, 2016.
Last checked: November 2026. The exact day must be verified by the editor.
Verdict badge: Disputed
Claim: Producers disagree about whether wooden rather than steel washbacks change the resulting spirit.
What the record shows: Glenfiddich reports better new make from wood, while Diageo cites sensory properties in retaining wood and Glenfarclas reports no difference after changing to steel. Sources and Glenfiddich account.
Evidence against or gap: Heriot-Watt described a direct comparison as an unanswered question in 2021; the sources recorded here do not establish a measured flavour difference. Source
Earliest source identified in the sheet: ScotchWhisky.com, 16 May 2016. Source
Last checked: November 2026. The exact day must be verified by the editor.
The answer remains disputed in the accounts available here. Glenfiddich reports better new make from wood, while the trade account says Diageo retains wooden washbacks because of the spirit’s sensory properties; Glenfarclas reports no difference from its change to steel. [1][7]
These statements should stay attached to the producers making them. They do not establish a universal rule that one material changes spirit in a particular direction, or that every distillery would obtain the same result. [1][7]
Heriot-Watt’s 2021 seminar synopsis called the influence of wood versus stainless steel a question “yet to be addressed”. It proposed that wooden washback microflora could increase methyl ketones, potentially contributing sour and fatty notes, but this was a research proposition rather than a demonstrated sensory result reported in the synopsis. [2]
That leaves a useful distinction: there is evidence for microbial persistence in wood and published discussion of flavour contributions, but the recorded research does not settle a direct material comparison. Choosing between the vessels cannot honestly be reduced to a guaranteed tasting note. [2][3][4]
Reading distillery examples fairly
Different distilleries also use different timbers and fermentation schedules. Springbank’s published process account, checked in November 2026, describes six washbacks made from boatskin larch and fermentation lasting up to 110 hours. [6]
The sponsored 2023 Glenfiddich article describes 48 handmade Douglas fir washbacks holding the liquid for 72 hours. These are figures from that dated account, not a current inventory or an industry-wide fermentation standard. [7]
Such examples help explain what a distillery means when it says it uses wooden washbacks. They do not isolate material as the cause of its spirit character: the examples describe different vessels and schedules, not a controlled comparison. [6][7]
Common mistakes
Treating wood as a flavouring ingredient. The resemblance to a maturation cask makes this an understandable assumption. The cited explanation instead points to surviving micro-organisms as contributors to wash flavour, rather than flavour extracted from the timber itself. [1][4]
Assuming easier cleaning means fermentation without microbes. The documented comparison concerns how reliably surfaces can be cleaned. The research also identifies raw materials and environmental factors as influences on wort populations, so vessel material is not the whole microbial story. [1][4]
Reading a producer preference as a scientific verdict. Distilleries’ judgements are valuable evidence about their own practice. The contrasting positions of Glenfiddich and Glenfarclas, alongside the research question identified by Heriot-Watt, are reasons to keep those judgements specific rather than turn them into a general ranking. [1][2][7]
Where to go next
- Mashing: How Grain Starches Become Fermentable Sugars: follow the stage that supplies wort to the washback.
- Fermentation: How the Wash Is Made: understand what happens after yeast is added.
- Lactic Acid Bacteria and Whisky Fermentation: examine the bacterial contribution in more detail.
Sources
- ScotchWhisky.com, The Whisky Professor. Are wooden washbacks better than steel?, 16 May 2016. Trade source. https://scotchwhisky.com/magazine/ask-the-professor/9275/are-wooden-washbacks-better-than-steel
- Heriot-Watt University, School of Engineering and Physical Sciences. Proctor, H. The Fungi, the Ketones and the Washback: The influence of distillery microflora on whisky flavour, seminar synopsis, 28 April 2021. https://projects.eps.hw.ac.uk/seminars/node/1672
- Heriot-Watt University, School of Engineering and Physical Sciences. Proctor, H. A longitudinal study of fungal communities on wooden washbacks and in washback wood at a Scotch Malt whisky distillery, seminar synopsis, 21 June 2023. https://projects.eps.hw.ac.uk/seminars/node/1902
- Daute, M., Jack, F., Harrison, B. and Walker, G. Experimental Whisky Fermentations: Influence of Wort Pretreatments. Foods, volume 10, issue 11, article 2755, 2021. https://pmc.ncbi.nlm.nih.gov/articles/PMC8624260/
- Department for Environment, Food and Rural Affairs. Technical File for Scotch Whisky, June 2019. Used for its process description, not a current legal conclusion. https://assets.publishing.service.gov.uk/media/5fd36667e90e07662ed92c85/Scotch_Whisky_Technical_File_-_June_2019.pdf
- Springbank Distillers. Our Process, undated, producer’s account. https://www.springbank.scot/about/process/
- Scottish Licensed Trade News. Davidson, G. Glenfiddich’s cutting edge take on tradition, 5 April 2023. Sponsored trade article. https://sltn.co.uk/2023/04/05/a-cutting-edge-take-on-tradition/
- Simpson, K. L., Pettersson, B. and Priest, F. G. Characterization of lactobacilli from Scotch malt whisky distilleries and description of Lactobacillus ferintoshensis sp. nov. Microbiology, volume 147, issue 4, pages 1007 to 1016, 2001. Abstract recorded through Europe PMC. https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=DOI:10.1099/00221287-147-4-1007&resultType=core&format=json
This desk-researched comparison follows the site’s verified fact sheet, separating peer-reviewed findings, seminar synopses and attributed producer views.
Last checked: November 2026