Direct Fired vs Steam Heated Stills
An open oil flame beneath the wash still, a copper chain sweeping its base: a 2014 engineering profile of Springbank captures direct firing at work.[8] The flame heats the pot from below. In a steam heated still, heat commonly comes through coils or pans inside it. That difference can create much hotter copper surfaces, changing how wash residues behave and potentially shaping the spirit’s character. The precise flavour mechanisms remain unresolved.[2][5]
Direct fired vs steam heated stills: the key differences
Both methods have the same task: heat the fermented liquid, called wash, so that vapours rise through the still neck towards the condenser. The Scotch Whisky Technical File describes this gradual heating as part of pot distillation.[1] For the wider sequence, see how whisky is distilled.
Still house engineer Briggs of Burton divides heating equipment into three groups: direct fired, internally heated and externally heated. Internal systems use coils or pans, most commonly heated by steam. External systems use plate or shell and tube heat exchangers.[2] The distinction is useful: an alternative to fire need not be a steam coil inside the pot.
| Heating arrangement | Where heat enters | Main distinction |
|---|---|---|
| Direct fired | Through the base above a flame | High copper surface temperatures; a rummager removes fouling.[2] |
| Internal coils or pans | Through surfaces inside the still | Usually steam heated; cleaning in place removes fouling.[2] |
| External heater | Through a separate heat exchanger | The wash does not boil inside the heat exchanger.[2] |
These are equipment categories, not flavour grades. Briggs describes heating as an important choice and says flexible equipment can help distillers select particular characteristics, without ranking one arrangement above another.[2]
What happens beneath a direct fired still?
Direct firing means a flame beneath the pot, not necessarily a coal fire. Briggs describes natural gas as the typical fuel; the published Springbank engineering account records an open oil flame beneath its wash still.[2][8] What defines the method is where the flame delivers its heat.
The Whisky Professor’s technical account describes a convex base that distributes the flame’s heat, with heavier copper to withstand the intense heating.[5] The base is an integral part of the heating system, rather than simply the bottom of a vessel above a burner.
Temperature comparisons depend on where the reading is taken. The accounts give different figures without establishing a comparable peak measurement: flame temperature and copper surface temperature are not interchangeable.[2][5]
For flavour, the crucial meeting point is between the wash and that hot copper. According to the Whisky Professor, residues can scorch onto the surface, producing browning reactions that can increase sulphur compounds and vegetal notes.[5] Managing those deposits is therefore part of working with direct fire, alongside its possible contribution to character.
Why the rummager matters
Copper chains or mats sweep across the base of the still, dragged by rotating arms. This moving assembly is the rummager. The Oxford Companion to Spirits and Cocktails explains that it stops solids settling and scorching while helping spread heat across the bottom.[6]
At Springbank, the 2014 engineering profile describes a copper chain rotating on an arm inside the wash still specifically to prevent solid deposition.[8] It is practical working equipment, not an ornamental survival from older production.
The Oxford Companion says steam coil heating made rummagers unnecessary.[6] Changing the heat source can therefore mean more than replacing a burner: it also changes the equipment needed to keep the heated surface clear.
How steam heating differs
Internal steam heating brings the heating surface into the still, as a coil or pan. In Briggs’ internal heating example, stainless steel surfaces operate at 135 to 152 °C.[2]
Those temperatures describe the equipment maker’s example, rather than every steam heated still. They illustrate the central engineering difference: the wash receives heat through an internal surface, at a different temperature, instead of through a base heated by flame.[2]
InchDairnie describes the sequence plainly. It first preheats its wash using waste heat, then uses steam inside the still to bring it to the boil.[4] Preheating and still heating are separate stages, both contributing to the wash reaching distillation temperature.
Steam and flame can also work together. The May 2014 profile records an external oil flame and internal steam coils in Springbank’s wash still, with a rotating rummager and steam coils in the spirit stills.[8] It describes the arrangement at that time, not necessarily the current configuration.
The same publication records steam entering Glen Scotia’s wash still through two kettles, with coils in its spirit still.[8] “Steam heated” covers more than one equipment design; the useful question is how a particular still is arranged.
What can heating change in flavour?
Direct firing can create deeper, more complex new make character, Suntory chief blender Shinji Fukuyo told the Whisky Professor. He also said: “We don’t know the mechanism.”[5] That pairing captures the strongest practical evidence: distillers recognise differences, while the technical explanation remains incomplete. The case rests on their experience and technical accounts rather than a controlled comparison isolating heating alone.
New make is the spirit before maturation. Fukuyo’s observation concerns that spirit, rather than a taste shared by every mature whisky made in a direct fired still.[5]
The Whisky Professor links direct firing with increased furfural, derived from the hemicellulose in barley husks. The account describes caramel and nutty notes at lower levels, reaching a burnt chocolate effect at the extreme.[5] These are explanations of possible character, not a set of tasting notes applicable to every direct fired whisky.
Briggs approaches flavour through Maillard reactions: the formation of flavour and colour involving amino acids, sugar, water, temperature and time.[2] Its presentation compares several heating methods, offering an engineering explanation rather than identifying which compounds account for a particular distillery’s character.
Heat is only one influence. The Scotch Whisky Technical File also identifies still design, distillation rate, copper contact and the fractions collected as factors shaping the distillate.[1] The guide to reflux and copper contact explores another part of that system.
Heating is a meaningful production choice. The available accounts do not establish a universal sensory signature. There is no sound basis here for identifying the heating method from one flavour alone, or for ranking fire above steam.[1][2][5]
Heat control and energy demand
The aim of direct firing is not to burn the wash. The Whisky Professor describes preheating and gradual temperature increases as ways to avoid burnt flavours, while noting that control is harder with flame than with steam.[5] This is a production distinction, not an operating method for readers to reproduce.
Energy demand gives the choice another dimension. A 2026 modelling study by Zhuang, White and Boulton found that distilling energy dominated total energy demand in the Scotch malt whisky production system modelled. Fermenter cooling energy was negligible.[3]
Briggs gives approximately 9.2 kWh per litre of pure alcohol for direct firing, compared with 7.2 kWh per litre of pure alcohol for internal coils or pans.[2] These are the equipment maker’s comparison figures, not measured averages across distilleries or predictions for an individual site.
The same presentation reports about a 40% reduction in batch distillation steam usage through thermal vapour recompression for Scotch wash distillation.[2] That reported reduction concerns steam usage in the stated application, not a distillery’s entire energy demand.
InchDairnie’s use of waste heat to preheat wash shows another route to recovering energy.[4] The engineering question reaches beyond “fire or steam”: how heat is supplied, recovered and reused matters too.
Common misunderstandings
“Direct fired means coal fired.” Briggs identifies natural gas as typical, while the Springbank engineering profile records oil firing.[2][8] The fuel and the heating arrangement are separate details.
“A burnt flavour is the objective.” The Whisky Professor describes controlling heat to avoid burnt notes; the rummager likewise prevents deposits from scorching.[5][6]
“The mechanism is scientifically settled.” Fukuyo’s acknowledgement of an unknown mechanism separates recognising a character difference from fully explaining it.[5]
The revealing detail is where the wash meets the heat: a flame heated copper base, an internal coil or a separate exchanger. Follow that point of contact and the comparison becomes clearer, from the rummager sweeping the bottom to the way heat is controlled, recovered and reused.[2][4][6]
Where to go next
- Pot Stills Explained: understand the vessel before comparing its heating equipment.
- Still Shape and Size: How They Shape Flavour: explore another design choice affecting distillation.
- The Cut: Heads, Hearts and Tails: follow how the fractions collected help shape the spirit.
Sources
[1] UK Government. Technical File for Scotch Whisky, June 2019.
https://assets.publishing.service.gov.uk/media/5fd36667e90e07662ed92c85/Scotch_Whisky_Technical_File_-_June_2019.pdf
[2] Briggs of Burton. Ludford-Brooks, J. Still Heating Technologies and Emulation of Direct Fired Character, conference presentation, Session 5, 31 May, WDSC2017, 2017. Equipment maker’s account.
https://briggsofburton.com/wp-content/uploads/technical-papers/LUDFORD-BROOKS-Session5-May31st_JLB-WDSC.pdf
[3] Zhuang, S., White, J. and Boulton, C. Quantifying the impact of increasing wash strength for Scotch malt whisky production: a modelling study. Journal of the Institute of Brewing, 132(2), 78 to 91, 2026. DOI: 10.58430/jib.v132i2.97.
https://jib.cibd.org.uk/index.php/jib/article/view/97
[4] InchDairnie Distillery. Our process, undated web page. Producer’s account.
https://www.inchdairniedistillery.com/our-process/
[5] ScotchWhisky.com. The Whisky Professor. Why some distilleries use fire-heated stills, 10 September 2019. Trade account.
https://scotchwhisky.com/magazine/ask-the-professor/27217/why-some-distilleries-use-fire-heated-stills/
[6] Risen, C. “rake or rummager”. The Oxford Companion to Spirits and Cocktails, edited by D. Wondrich and N. Rothbaum, online dictionary entry, publication year not supplied in the fact sheet.
https://www.spiritsanddistilling.com/dictionary/acref-9780199311132-e-644
[8] Mitchell, B. Och! Campbeltown Loch... Brewer and Distiller International, May 2014, pp. 33 to 38, Institute of Brewing and Distilling.
https://www.cibd.org.uk/media/5e2hin4o/5-campbeltown.pdf
This desk research article uses the supplied verified fact sheet, distinguishing equipment maker and producer accounts from research, reference works and trade reporting.
Last checked: November 2026