Sulphur in Whisky: Copper Contact, Sherry Casks and Struck Match Notes
Cooked sweet corn, onion, meat and rotten cabbage: a 2022 scientific review reports more than forty sulphur compounds in whisky, with strikingly different odours.[1] Their story begins well before a sherry cask enters the picture, in barley, fermentation and distillation.
Copper contact helps reduce sulphury compounds, and maturation changes them further. Some contribute positively at low levels and negatively at high levels. A struck match aroma describes what reaches the nose, but cannot, on its own, identify where it came from.[1]
What sulphur in whisky actually means
“Sulphur” is a broad sensory label, not one smell. Wanikawa and Sugimoto’s review describes a family of compounds whose odours range from cooked sweet corn to onion, meat and rotten cabbage.[1]
A blender praising a meaty component and a drinker objecting to rotten vegetables may both be discussing sulphury character. They need not be smelling the same compound, or judging the same sensory effect.[1][3]
The review gives the following odours for individual compounds. These are reference descriptors, not tasting notes for a particular bottle.[1]
| Compound | Abbreviation | Odour reported in the review |
|---|---|---|
| Dimethyl sulfide | DMS | Cooked sweet corn |
| Dimethyl disulfide | DMDS | Vegetable |
| Dimethyl trisulfide | DMTS | Onion, meaty |
| Ethanethiol | None used here | Leek |
| Methanethiol | None used here | Rotten cabbage |
| Hydrogen sulfide | None used here | Rotten egg |
| Methional | None used here | Onion, meaty |
Source: Wanikawa and Sugimoto, 2022.[1]
A sensory wheel cited in the same review places “struck match” alongside cooked vegetable, rubbery, decaying and meaty attributes. It is useful descriptive language, rather than a chemical identification or a diagnosis of cask treatment.[1]
For the wider relationship between compounds and aroma, see whisky flavour chemistry. The distinction to keep in mind is simple: describing a smell and establishing its cause are different tasks.
Where sulphur enters the process
Sulphur chemistry begins in the barley. During germination, S-methylmethionine forms from the amino acid methionine; during kilning, it can become DMS. The review reports increased DMS at higher kilning temperatures.[1]
Fermentation opens another route. Yeast takes up sulphate to make sulphur-containing amino acids, while hydrogen sulfide can become ethanethiol and related compounds. Research summarised in the review also found stronger cereal, sulphury and feinty notes with brewer’s yeasts.[1]
Dave Waddell’s trade account identifies fermentation as the main source, with smaller contributions from germination, kilning and mashing. This is an industry interpretation, not a measured allocation of every sulphur compound in every whisky.[3]
A 1998 Heriot-Watt study makes a more specific connection. Its abstract reports a correlation between methional in wash, the fermented liquid, and DMDS in grain spirit produced with a Coffey still. It identifies methional as a possible precursor and says still operation could affect final DMTS levels.[2]
Compounds form and change throughout these stages. By the time spirit reaches a previously used cask, sulphur chemistry is already part of its history.[1][2]
Why copper contact matters
Copper does more than give a still its familiar appearance: it changes the spirit’s chemistry. The 2022 review reports that copper contact with liquid in the pot and vapour in the lyne arm, the pipe leading away from the still, was particularly important in reducing sulphur compounds. In its account, the pot had the largest effect.[1]
The underlying experiments compared copper in different parts of malt whisky pot stills. Location mattered: a still that “contains copper” tells only part of the story. The crucial question is which liquid or vapour meets it.[1]
Studies summarised in the review found higher sulphury sensory scores with non-copper distillation. Unknown analytical peaks appeared particularly in distillate from a stainless steel still and were considered possible contributors to meaty and sulphury notes.[1]
Copper’s chemistry also has a complication. In model solutions, copper ions promoted the formation of DMDS and DMTS from thiols and hydrogen sulfide. This laboratory finding does not overturn the still experiments, but it prevents the simpler claim that copper always destroys every sulphur compound under every condition.[1]
| Stage | What the evidence describes | What it does not establish |
|---|---|---|
| Malting | A DMS precursor forms during germination and can convert to DMS during kilning.[1] | The cause of a particular bottle’s aroma. |
| Fermentation | Yeast pathways produce sulphur compounds and precursors.[1][2] | One fixed sulphur level for all fermentations. |
| Distillation | Copper contact reduces sulphury character in experimental comparisons.[1] | Identical effects at every point in a still. |
| Maturation | Sulphur compounds decline at different rates.[1] | A universal timetable for their disappearance. |
Worm tubs and meaty spirit
Heavier, meatier spirit can be a style worth preserving. A worm tub is a condenser, one of the places where spirit vapour becomes liquid, and the review associates worm tub condensation with greater sulphury and heavier notes. It also reports a study in which one measured sulphur compound was lower with a worm tub. Condenser type matters, without explaining every compound on its own.[1]
Trade accounts connect older production practices, including squat stills, long fermentations and worm tubs, with meatier spirit valued by blenders. Waddell describes shell and tube condensers as reducing this character.[3]
“Sulphur equals fault” is therefore too blunt a rule. The review describes positive contributions at low levels and negative contributions at high levels; the trade account gives meaty spirit a role in blending.[1][3]
Verdict badge: sulphur as fault or style
Claim: Sulphury character in whisky is a fault rather than a desirable style.
Verdict: Disputed.
What the record shows: The review distinguishes positive and negative contributions by level; the trade account describes meaty spirit as valued for blending.
Evidence against or gap: The accounts differ in emphasis, and a sensory judgement need not apply equally to every compound or concentration.
Earliest known source: Not established from the sources checked.
Sources: Wanikawa and Sugimoto, 2022; Waddell, 2015.
Last checked: Exact date not documented.
What maturation changes
Time in a cask changes sulphur compounds at different speeds. The review describes DMS falling markedly, DMDS declining gradually and DMTS declining slowly, linking reductions to evaporation and the cask’s charcoal layer.[1]
Another study reported in the review found no change in DMTS, benzothiophene and benzothiazole, while other compounds decreased markedly within a few years. Maturation is selective: these findings do not promise that time will erase every sulphury note.[1]
“Sulphur fades” captures some observed trends, but loses those differences. The evidence offers neither a guaranteed number of years nor an assurance that a particular sulphury aroma will disappear.[1]
Sherry casks, wine sulphiting and sulphur wicks
Sulphiting wine and burning a sulphur wick inside an empty barrel are distinct practices. Both involve sulphur dioxide, but they treat different things.
The International Organisation of Vine and Wine defines wine sulphiting as adding gaseous sulphur dioxide, sulphuric solutions or potassium metabisulphite solutions to wine, with microbial stability and antioxidant protection among its purposes.[7]
Méchage concerns the empty barrel instead. Cavesa’s wine glossary describes burning a sulphur wick inside an empty barrel to sanitise its interior, producing sulphur dioxide gas.[8]
These definitions explain the practices, not the treatment history of a particular whisky cask. A sulphury aroma alone cannot distinguish wick treatment from compounds originating in malting, fermentation or distillation.[1][7][8]
The Consejo Regulador’s 2021 specification for its “Sherry Cask” brand addresses wine seasoning. Among its requirements, casks must be seasoned with registered wines in the Jerez production area for at least one year, with certification verified by Fundación OECCA.[10]
The specification does not mention sulphur or sulphur wicks. It establishes its stated seasoning requirements, confirming neither that wick treatment occurred nor that it was prohibited.[10]
Nor does every whisky sherry cask necessarily have years of solera service behind it. The branded specification requires at least one year of seasoning, which is different from establishing a long working life in a solera.[10]
Common mistakes when interpreting sulphur
Assuming a struck match note identifies a sulphured sherry cask. Empty-barrel sulphur treatment exists, which makes the association understandable. The review, however, documents several production sources of sulphur compounds and lists struck match as a sensory descriptor without tying it to one cause.[1][8]
Treating every sulphury note as a fault. Rotten vegetable and other strongly unpleasant descriptors can dominate the discussion. Yet the review also recognises positive contributions at low levels, and trade accounts document a place for meaty spirit in blending.[1][3]
Assuming all sulphur disappears with age. Different compounds follow different paths. The review reports substantial reductions for some, slower change or persistence for others.[1]
Story box: Struck match and sherry casks
Founding story: Not applicable.
Documented record: Struck match appears among the review’s sulphury descriptors; several production sources are documented. Wanikawa and Sugimoto, 2022
Legend or tradition: The automatic link to a sulphur treated sherry cask is classed as Legend in the fact sheet. Its earliest source is not established.
Last checked: Exact date not documented.
Verdict badge: struck match and sherry casks
- Claim: A struck match aroma always means a whisky came from a sulphur-treated sherry cask.
- Verdict: Legend.
- What the record shows: A recognised descriptor, with several documented production origins for sulphur compounds.[1]
- Evidence against or gap: The review establishes no unique connection between this aroma and cask treatment.[1]
- Earliest known source: Not established from the sources checked.
- Sources: Wanikawa and Sugimoto, 2022.
- Last checked: Exact date not documented.
Where to go next
- The Chemistry of Whisky Flavour: place sulphur compounds in the wider picture of whisky aroma.
- What Happens When You Add Water to Whisky?: explore a separate question about whisky in the glass.
- What Causes Haze in Whisky?: distinguish appearance from aroma.
Sources
[1] Wanikawa, A. and Sugimoto, T. A Narrative Review of Sulfur Compounds in Whisk(e)y. Molecules 27(5), 1672, 2022. https://pmc.ncbi.nlm.nih.gov/articles/PMC8911989/
[2] Prentice, R. D. M., McKernan, G. and Bryce, J. H. A source of dimethyl disulfide and dimethyl trisulfide in grain spirit produced with a Coffey still. Journal of the American Society of Brewing Chemists 56(3), 99 to 103, 1998. Heriot-Watt University research portal record and abstract. https://researchportal.hw.ac.uk/en/publications/a-source-of-dimethyl-disulfide-and-dimethyl-trisulfide-in-grain-s/
[3] Waddell, D. There's nothing wrong with sulphur. ScotchWhisky.com, 25 September 2015. Trade commentary. https://scotchwhisky.com/magazine/the-way-i-see-it/6740/there-s-nothing-wrong-with-sulphur/
[7] International Organisation of Vine and Wine. International Code of Oenological Practices: Sulphiting (wine chapter). Resolution OENO 7/2003. https://www.oiv.int/node/3681
[8] Cavesa. Méchage. Wine merchant glossary, undated. https://www.cavesa.ch/en/definition/mechage
[10] Consejo Regulador Jerez-Xérès-Sherry. Envinado (Wine-Seasoning) Technical Specifications. Revision 03, 23 March 2021. https://www.sherry.wine/documents/183/especificacion_tecnica_de_envinado_ingles_rev_03_2.pdf
This desk-researched article uses the supplied verified fact sheet, distinguishing scientific review findings, a research abstract, trade commentary and wine-seasoning specifications.
Last checked: November 2026