How Scotch whisky is made

The step-by-step process from field to cask

ABSTRACT

Whisky begins with three ingredients: water, grain, and yeast. The process appears straightforward: steep barley, sprout it, dry it, grind it, add hot water, ferment, distil twice, fill a cask, wait. Most accounts of whisky production describe these steps as a sequence, and they are; but the simplicity of the list disguises an extraordinary density of biochemistry at every stage.

When researchers began testing the variables within each stage—the temperature of the mash, the format of the yeast, the geometry of the still, the depth of the char on the cask—they found that even small adjustments produced measurable and significant differences in the flavour compounds that carry through to the finished spirit. What looks like a recipe is, in fact, a series of interlocking decisions, and each one shapes the flavours of the whisky that will eventually fill the glass.

This article traces the whisky making process from the farm and through the cask, drawing on peer-reviewed scientific literature to explain what is happening at each stage and why it matters. It is an overview, not a deep dive into any single step—those will follow in dedicated articles—but it is grounded in the research, and the key claims are sourced to specific studies.

Because it’s an overview, this article isn’t paywalled. And we’ll come back to link future articles, creating a beautiful digital web of deep dives from this one anchor article. If you like this article or learned something, consider becoming a paid subscriber so that you can take advantage of that academic web!

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Setting the scene

There is a point, early in any distillery visit, when the guide stops talking about history and starts talking about grain.

It’s usually at the mash tun, or at a display of barley in a glass jar, or at a photograph of a field. The story always begins the same way: water, barley, yeast. Three ingredients. It’s so simple. And then, over the next hour, you walk through a building in which those three ingredients are subjected to a sequence of transformations so precise and so interdependent that a single variable changed at any point—the temperature of the water, the strain of the yeast, the angle of a copper pipe—would produce a different spirit entirely.

And so, this article peels back the romance of the thing, highlighting the mechanics of it all: what happens, in what order, and why each step matters to what ends up in the glass.

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Grain: the foundation

Whisky begins long before the distillery. It begins in a field, with the selection of a grain variety, and—for single malt Scotch—that grain is always barley. The barley plant has been cultivated for roughly ten thousand years, and for most of that time it has served as a staple crop. Its use in fermentation came early, but its domestication as a specifically distilling-grade ingredient is a more recent and more precise science.^[1]

Distilling barley is not the same as brewing barley, and it is not the same as feed barley. The attributes a distiller requires are distinct: high potential spirit yield, strong enzymatic activity, and an absence of the gene responsible for producing glycoprotein nitrogen compounds, which can cause haze in the final spirit. Modern distilling varieties are bred to maximise spirit yield from a given weight of grain, and maltsters select consignments against tight specifications for moisture content, germination energy, and enzyme development.^[2]

Critically, the distiller does not boil the wort the way a brewer does. Boiling destroys the diastatic enzymes the malt has produced—enzymes the distillery needs to remain active through mashing. That single difference in process shapes every decision that follows.^[3]

(We did interviews with a barley farmer, maltster, and merchant. They’re interesting, primary sources on the world of Scottish barley farming.)

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Malting: waking the grain

Before barley can contribute its starch to fermentation, that starch must be made accessible. The purpose of malting is to coax the grain into beginning germination—to activate its enzymes—and then to arrest that germination before the plant consumes the resources the distiller needs.

The process has three stages: steeping, germination, and kilning. Steeping saturates the grain with water, triggering the onset of growth. During germination, the grain is spread across the malt floor—or loaded into mechanised turning drums—and allowed to sprout for several days. Enzymes are activated and begin breaking down the cell walls and protein matrix that surround the starch granules, making the starch accessible for conversion to fermentable sugars.

The maltster’s job is to encourage this process to proceed far enough that the starch is fully accessible, but not so far that the young plant’s rootlets consume the starch as fuel. When modification is considered complete, the grain is moved to the kiln.

A bit more on peating

The kiln is where character diverges sharply between distilleries. Malt is dried using hot air driven through a perforated floor. If that air is first passed over burning peat, phenolic compounds from the smoke—including guaiacol, cresols, phenol, xylenols, and furfurals—are absorbed onto the surface of the grain. The quantity absorbed is measured in parts per million of phenol, and it becomes one of the most defining variables in the character of the final spirit.^[4]

The peats used at different Scottish locations differ meaningfully in their botanical composition. Analysis identifies distinct differences between Islay, Aberdeenshire, and Orkney peat sources, each producing a different phenolic signature.^[5] Unpeated malt is dried using only hot air. The phenolic level fixed during kilning carries through mashing and fermentation and is not recoverable; once set, it defines the phenolic ceiling of the spirit.

After kilning, the malt is rested and then ground in a mill. Malt moisture must be managed carefully at this point: malt above 5% moisture causes problems on a standard distillery 4-roll mill, and risks introducing sulphury, green malt notes to the spirit.^[6]

(More on peat in this primer article.)

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Mashing: releasing the sugars

Ground malt—now called grist—is mixed with hot water in a vessel called a mash tun to extract its fermentable sugars. The chemistry here depends on temperature. Different enzymes operate at different thermal optima, and the distiller sequences the water additions to extract the maximum quantity of fermentable material.

The first water is typically added at around 64.5°C.^[7] Alpha amylase, which breaks starch into shorter dextrin chains, is most active at higher temperatures. Beta amylase, which cleaves those chains into fermentable maltose, operates best at lower temperatures. The distiller keeps the initial mash temperature low enough to preserve beta-amylase activity, unlike the brewer, who kills it to produce unfermentable dextrins for body and mouthfeel in beer.

The liquid drawn off from the mash tun—the wort—is rich in maltose, glucose, and longer-chain sugars. It also contains free amino nitrogen, the pool of nitrogenous compounds—amino acids, small peptides, and ammonium ions—that yeast will draw on during fermentation. A free amino nitrogen level of approximately 150 mg/L is considered sufficient to support healthy yeast growth. Below that threshold, nitrogen-starved yeast may produce higher levels of undesirable congeners as a metabolic stress response.^[8]

The spent grain solids left behind—draff—are a co-product. Most distilleries now burn draff in biomass burners for energy recovery, though some still sell it as cattle feed. The wort is cooled before transfer to the washback.

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Fermentation: building complexity

The wort is cooled and transferred into washbacks—large vessels made from wood or stainless steel—and yeast is pitched. What follows over the next 48 to 122 hours is a dense biological negotiation between yeast metabolism and the chemical environment it inhabits.^[9]

Distilling yeasts are selected for specific attributes that differ from brewing yeast strains. They must tolerate higher alcohol concentrations and ferment the full range of carbohydrates present in the wort. The format of the yeast also matters: liquid yeast enters fermentation with a 68% shorter lag phase than dried yeast, which means it begins producing alcohol before the bacterial population in the washback can establish itself.^[10]

During the early stages of fermentation, while yeast is still establishing dominance, Lactobacillus bacteria compete in the washback. At longer fermentation times—the slower, later period after yeast has consumed the available sugar—bacterial activity increases, producing lactic acid and a range of esters. This is a recognised driver of flavour complexity in the resulting wash rather than an incidental contamination.

A bit more on fermentation time and spirit character

Reid et al. demonstrate that liquid yeast, compared to dried formats, produces higher ester concentrations in the final new make spirit, with statistically significant differences in both ethyl esters and acetate esters.^[11] This points to fermentation management—including the choice of yeast format and the duration of fermentation—as a meaningful lever for spirit character, which is distinct from distillation or maturation.

The yeast converts the wort’s fermentable sugars into ethanol and carbon dioxide. That much is familiar. Less visible in popular accounts is the simultaneous production of hundreds of congeners—organic acids, esters, fusel alcohols, aldehydes, and sulphur compounds—that will carry through into the distillate and contribute to the eventual character of the spirit. The target wash ABV at the end of fermentation is 8–10%.^[12]

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Distillation: concentrating and selecting

The wash enters the still. For single malt Scotch, the still is a pot still: a copper vessel with a distinctive shape that varies from distillery to distillery, connected via a swan neck and lyne arm to a condenser. The shape of that vessel and the angle of the lyne arm are cute, but they’re not aesthetic choices. They determine the degree of reflux—the rate at which partially vaporised spirit condenses inside the still and falls back—which shapes the character of what passes through.

Single malt Scotch is typically distilled twice. The first distillation in the wash still separates the bulk of the alcohol from the spent wash, producing a liquid called low wines at approximately 20–25% ABV. The second distillation in the spirit still is where the distiller makes the most consequential decisions of the process: the cuts.

There are a few Scottish distilleries, including Springbank for its Hazelburn brand, that triple distil…but that tends to be more of an Irish whiskey thing.

A bit more on reflux and spirit character

The swan neck and lyne arm are passive reflux mechanisms. A taller, narrower still with a more steeply ascending lyne arm forces more vapour to condense before it can pass into the condenser, returning heavier, oilier compounds to the pot and allowing only lighter, more volatile fractions to pass through. A shorter, wider still with a downward-angled lyne arm allows heavier compounds to pass more easily, producing a heavier, more complex spirit.

(We took a deep dive into copper contact in this article.)

Picard et al. demonstrate that reduced natural reflux during foreshots, combined with gradual, stepwise heart distillation, significantly enhances the floral intensity and aromatic complexity of the new make spirit.^[13] Specifically, linalool, β-citronellol, and β-damascenone are all elevated under these conditions. Sensory reconstitution confirmed synergism between esters, monoterpenes, and β-damascenone, amplifying floral perception beyond individual contributions.^[14]

In the spirit still, the distillate is divided into three fractions. The foreshots—the first fraction to run—are rich in short-chain esters and long-chain compounds, as well as methanol and other low-boiling volatiles. They are not collected for maturation.^[15] The heart—the fraction the distiller retains—contains medium-chain esters and constitutes the new make spirit that will fill casks.^[16] The feints—the final fraction—are rich in carboxylic acids and long-chain esters. Foreshots and feints are recycled back into the next distillation run.^[17]

Throughout this process, congeners behave according to the ethanol content of the boiling liquid: as the still runs down, the composition of what is passing through changes continuously, and the distiller’s art is in recognising—by smell, by instruments, or by experience—the precise moment at which to make the cut.

New make spirit leaves the spirit still at 57–70% ABV.^[18] Copper plays a specific and well-documented role throughout distillation: the metal catalyses the decomposition of sulphur compounds formed during fermentation that are unpleasant at detectable concentrations. The extent to which the spirit contacts copper—determined by still geometry, fill level, and distillation speed—is therefore another variable that shapes the final congener profile.

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Let’s chat about sulphur

Sulphur compounds in whisky deserve particular attention because they are produced at multiple stages and interact with the spirit differently depending on concentration. Wanikawa and Sugimoto report that more than forty sulphur volatiles have been identified, formed during malting, fermentation, and distillation.^[19]

In sensory analysis, sulphur characteristics are described as sulfury, meaty, cereal, feinty, and vegetable, among others. Their contribution to overall quality depends on concentration, with a positive contribution at low levels but a negative contribution at high levels.^[20] Both copper contact during distillation and the passage of time during maturation reduce sulphur compound levels, but the baseline is set during production. A distillery running short distillations on lightly copper-contacted stills with rapid fermentation is working against itself on sulphur.

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Maturation: made in the cask

New make spirit is not whisky. By law in Scotland, it must spend a minimum of three years in an oak cask before it can be called Scotch whisky.^[21] In practice, most single malts spend far longer. That makes the cask an active participant in the transformation of spirit into whisky.

American white oak and European oak are the species most commonly used in cask production. The oak’s internal structure determines how spirit interacts with the wood. In American white oak, tyloses—balloon-like outgrowths of parenchyma cells—occlude the conducting vessels of the wood, making it liquid-tight without the need for wax coating. The wood also contains significant levels of lactones, vanilla-precursor compounds, and tannins that dissolve into the spirit over time.^[22]

Maturation is an active process of slow dissolution. Scott et al. demonstrate that temperature cycling drives spirit into and out of the oak staves on a daily and seasonal basis.^[23] As temperature rises, spirit expands and is forced into the pores of the wood. As it cools, it contracts and pulls back, now enriched with compounds extracted from the oak.^[24] This cycling mechanism is one reason that warehouse location—stone-floored versus racked, coastal versus inland—does, in fact, affect the rate and character of maturation.

Charring the interior of the cask before filling is a critical preparatory step. The char layer acts as a form of activated carbon, adsorbing undesirable sulphur compounds and aldehydes present in new make spirit. Beneath the char, a layer of wood modified by heat releases colour compounds, lactones, and caramelised sugars into the spirit.^[25] Reep et al. show that char gradients—produced by methods such as blowtorch charring—increase the production of ethyl esters, particularly in the early stages of aging, and that different charring methods and temperatures influence which compounds are preferentially extracted.^[26]

Cask size matters in a very direct way: a 200-litre barrel has a higher surface-area-to-volume ratio than a 500-litre hogshead, so the spirit in a smaller cask contacts proportionally more wood per unit of liquid. Previous use of the cask also shapes what it contributes. A cask that held Sherry, Port, or Bourbon brings residual compounds from its former contents into the whisky’s maturation environment—a variable the distiller selects deliberately.

And, it’s worth noting: according to Scotch whisky regulations, nothing extra can be added to the spirit besides some caramel colouring. But, if there’s some leftover Sherry, Port, Bourbon, or other residual liquid in the cask, it’s technically not considering adding. Therefore, a ‘wet’ cask might have a bit more flavour—and liquid—mixed in.

What leaves the warehouse is not what entered it. Some spirit evaporates through the stave—the so-called Angel’s Share—estimated at approximately 1.2% of a 200-litre barrel per year under certain warehouse conditions.^[27] What remains is concentrated, coloured, and transformed: a spirit shaped by grain, shaped by fire, shaped by copper, and shaped by time.

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Back to the distillery

The guide finishes the tour at the warehouse. The air is different in here: cool, damp, sweet with the smell of oak and vanillin and slow evaporation.

Somewhere in one of these casks, a spirit is sitting that was made from barley grown in a field, malted in a kiln, mashed in hot water, fermented by yeast, distilled through copper, and placed in this wood years ago. Every one of those steps left a mark. The grain set the enzymatic potential. The peat—or its absence—fixed the phenolic ceiling. The mash temperature determined the fermentability of the wort. The yeast built the ester architecture. The still selected from what fermentation had created. The cask is transforming all of it, slowly, into something worth drinking.

Remove any one of those steps and the spirit in the glass is a different spirit. It’s as much art as it biochemistry, and the volume of variables makes the outcome an exciting mystery.

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References

Bathgate, George N. 2019. “The Influence of Malt and Wort Processing on Spirit Character: The Lost Styles of Scotch Malt Whisky.” Journal of the Institute of Brewing 125 (2): 200–213. https://doi.org/10.1002/jib.556.

Bringhurst, T.A. 2015. “125th Anniversary Review: Barley Research in Relation to Scotch Whisky Production: A Journey to New Frontiers.” Journal of the Institute of Brewing 121: 1–18. https://doi.org/10.1002/jib.192.

Daute, Martina, Irene Baxter, Barry Harrison, Graeme Walker, and Frances Jack. 2023. “From Fermented Wash to New Make Spirit: Assessing the Evolution of Flavour Characteristics of Scotch Whisky Using Lab-Scale Process Simulations.” Beverages 9 (2): 37. https://doi.org/10.3390/beverages9020037.

Picard, Magali, Esteban Muller, Ivan Lainé, Clément Chambolle, Justine Garbay, and Georgia Lytra. 2025. “Impact of the Rate of Spirit Distillation on Floral Aromas in Single Malt Whisky.” Journal of the Institute of Brewing 131 (4): 257–277. https://doi.org/10.58430/jib.v131i4.82.

Reep, Jonathan, David Morrisset, Stuart Martin, and Rory M. Hadden. 2025. “Assessing the Extent of Charring and Its Impact on the Whisky Ageing Process.” Food Physics 2: 100055. https://doi.org/10.1016/j.foodp.2025.100055.

Reid, Struan J., R. Alex Speers, William B. Lumsden, Nicholas A. Willoughby, and Dawn L. Maskell. 2023. “The Influence of Yeast Format and Pitching Rate on Scotch Malt Whisky Fermentation Kinetics and Congeners.” Journal of the Institute of Brewing 129 (2): 110–127. https://doi.org/10.58430/jib.v129i2.18.

Scott, Taylor E., Jarrad Gollihue, Michael P. Sama, Michael Shaffer, and Brad J. Berron. 2026. “The Transport of New Make Spirits Through American White Oak: Implications for Maturation.” Journal of the Institute of Brewing 132 (1): 17–28. https://doi.org/10.58430/jib.v132i1.87.

Wanikawa, Akira, and Toshikazu Sugimoto. 2022. “A Narrative Review of Sulfur Compounds in Whisk(e)y.” Molecules 27 (5): 1672. https://doi.org/10.3390/molecules27051672.

Footnotes

[1] Bringhurst 2015, p. 2. “Barley (Hordeum vulgare) was one of the first cereals domesticated by humans, probably in the ‘fertile crescent’ in the Middle East (Turkey/Lebanon/Syria/Iraq) at least 10,000 years ago.”

[2] Bringhurst 2015, pp. 3–4 (Table 1). Agreed attributes for Scotch whisky malt distilling barley: maximum alcohol yield potential, protein modification (including free amino nitrogen), and EPH non-producer screening via genetic marker.

[3] Bringhurst 2015, p. 1. “The fundamental difference between distilling and brewing production practices is that Scotch whisky distillers do not boil their worts, since they need to retain the maximum levels of endogenous enzyme activity into the fermentation process, to ensure that as much of the starch as possible is hydrolysed to fermentable sugars.”

[4] Bathgate 2019, p. 204. The phenolic group of peat smoke is “represented by guaiacol (2-methoxy phenol), phenol, ortho-, meta- and para-cresol (methyl phenol), 2:4, 2:5 and 3:5 xylenol (dimethyl phenol) and ethyl phenol.” The furfural group is represented by furfural and 5-methyl furfural.

[5] Bathgate 2019, p. 207 (Table 3). Comparison of peated malts from Islay, Aberdeen, and Orkney. Each source produces a distinct phenolic profile. The Orkney peat had “a much higher content of fibrous organic matter than both Aberdeenshire and Islay peat.”

[6] Bathgate 2019, p. 202. “Malt moistures >5% are not advisable on two counts. Firstly, malt grinding on a standard distillery 4-roll mill becomes problematic and secondly there is the danger of introducing sulphury, green malt notes to the spirit. This is particularly true for the potent marker compound dimethyl sulphide (DMS).”

[7] Bathgate 2019, p. 208. “The first mash was mixed with water at 64.5°C at a grist-to-liquor ratio of 1:4.”

[8] Bathgate 2019, p. 201. “A minimum FAN wort concentration of 150 mg/L is sufficient to ensure optimum yeast growth and anything above that level is surplus to requirements.”

[9] Daute et al. 2023, p. 2. “After a fermentation time of 48 h to 122 h and once an alcohol by volume (ABV) of 8–10% v/v has been reached, the fermented wash is distilled.”

[10] Reid et al. 2023, abstract. “The liquid yeast format demonstrated a significant reduction (p<0.05) in lag time, which was 68% shorter than dried yeast.”

[11] Reid et al. 2023, p. 117. “The concentration of volatile esters (except for ethyl acetate and phenylethyl acetate) was significantly (p<0.05) higher where the liquid format” was used.

[12] Daute et al. 2023, p. 2. “After a fermentation time of 48 h to 122 h and once an alcohol by volume (ABV) of 8–10% v/v has been reached.”

[13] Picard et al. 2025, abstract. “Reduced natural reflux during foreshots, combined with gradual, stepwise heart distillation, significantly enhanced the floral intensity and aromatic complexity.”

[14] Picard et al. 2025, abstract. “Optimised conditions increased the levels of linalool, β-citronellol, β-damascenone, and some esters. Sensory reconstitution confirmed the synergism between esters, monoterpenes, and β-damascenone, amplifying floral perception beyond individual contributions.”

[15] Daute et al. 2023, p. 2. “The foreshots contain highly volatile compounds such as short-chain esters, with carbon chain lengths smaller than 6, and long-chain fatty acids and esters, with carbon chain lengths longer than 14.”

[16] Daute et al. 2023, p. 2. “The next cut, the new make spirit, contains a large variety of congeners, with high levels of medium-chain esters with carbon chain lengths between 6 and 12.”

[17] Daute et al. 2023, p. 2. “The last cut, the feints, consists of congeners with high boiling points such as carboxylic acids and long-chain esters with carbon chain lengths longer than 12.”

[18] Daute et al. 2023, p. 2. “The new make spirit, which typically has an ABV of 57–70% v/v.”

[19] Wanikawa and Sugimoto 2022, abstract. “More than forty compounds have been reported: they are formed during malting, fermentation, and distillation, but some may decrease in concentration during distillation and maturation.”

[20] Wanikawa and Sugimoto 2022, abstract. “In sensory analysis, sulfur characteristics are described as sulfury, meaty, cereal, feinty, and vegetable, among others. Their contribution to overall quality depends on their concentration, with a positive contribution at low levels, but a negative contribution at high levels.”

[21] Reep et al. 2025, p. 1. “In the U.K., legislation dictates that Scotch whisky must be aged in oak casks for a minimum of three years.”

[22] Scott et al. 2026, p. 18 (citing Siau 1984; del Alamo-Sanza and Nevares 2018; Kim et al. 2024). “Tyloses significantly reduce permeability, as they completely occlude the conducting vessels.”

[23] Scott et al. 2026, p. 18. “As the barrel cycles in temperature, the liquid expands and penetrates the staves of the barrel and then flows back out of the wood.”

[24] Scott et al. 2026, p. 18. “The liquid flowing out of the wood carries wood constituents” back into the spirit.

[25] Reep et al. 2025, abstract. “The presence of a char gradient, arising from the use of a blowtorch, increased the production of ethyl esters, particularly significant during the early stages of the aging process.”

[26] Reep et al. 2025, results (pp. 3–7). Oak charred using muffle furnace (423–873 K), hotplate (1073 K), and blowtorch (~1373 K) produced different ester profiles. The blowtorch-charred samples “led to much greater levels of the investigated esters from the first sampling point onwards.”

[27] Scott et al. 2026, abstract. “A predicted average annual liquid loss of 1.2 ± 0.3% was calculated for non-leakage losses from a standard bourbon barrel (200L) matured in Kentucky.”