Scotch whisky has a long and distinguished pedigree in the minds of connoisseurs. What they may not realize is the exquisite care that is used to craft the perfect amber liquid they are sipping. Scotch was not always the drink of choice – even in the British Isles. Prior to the crash in demand in the first half of the 20th century, Irish Whiskey held pride of place among grain alcohol brewed in Britain. Now, of course, the picture is different. The aura of Single Malt Scotch whisky revolves around the subtle flavour, aromas and mouthfeel that are developed by master distillers., the culmination of more than 700 years of experience in the craft.
It’s important to realise that the steps to produce Scotch whisky recounted below are generalised steps – master distillers in Scotland often have their own, patented processes that produce unique flavours.
History of Whisky
The processes of fermentation and distillation to create alcoholic spirits date back thousands of years. We find references in ancient Babylon, Egypt, India, China, Greece and Rome, to name just a few civilizations in antiquity. Alcoholic spirits were introduced in Britain by the Romans, likely in the 13th or 14th century. The name whisky came from the Scots Gaelic term “Uisge beatha”, which arose from the Latin name “aqua vitae” (“water of life”, a reference to distilled spirits) and was later translated to “uske” before it reached the modern name.
By the early 18th century, the name whisky was being referred to in Scottish written records. The battle between Scotch and Irish whiskies went on for another 200 years, through a period when cheap blended Scotches flooded the market after to the invention of the continuous still (more on that below) by Aeneas Coffey in the mid 19th century, following which the major Irish distilleries rose in indignation at cheap imitations. Finally, post-World War I, a real appreciation for Scotch whisky began to emerge – first in England, then elsewhere in the British Dominion, including Canada, India and Australia.
By this point, Scotch had come a long way. Though blended whisky (which was malt whisky blended with other, cheaper, grain alcohol) had definitely made an impression, the market for Single Malt Scotch, the crème de la crème, had grown significantly – to the point where major distilleries could stamp their identity and brand their products separately from the run of the mill production. Scotch whisky had arrived, a position it holds to this very day.
The Legal Definition of Scotch Whisky
By the mandate of the Scotch Whisky Regulations of 2009, Scotch whisky must be produced in a distillery at Scotland as follows:
- With principal ingredients being water and malted barley (to which only whole grains of other cereals may be added);
- Processed at the distillery into a mash;
- Converted … to a fermentable substrate only by endogenous enzyme systems;
- Fermented … only by adding yeast; and
- (At least twice) Distilled at a strength of less than 94.8% alcohol by volume (ABV) or US 190 Proof.
Upon production, the distilled liquor must further be:
- Aged in oak casks for no less than three years at an excise warehouse in Scotland (this is for value-added tax payment purposes);
- Retains the (original) colour, aroma and taste (of the original materials and production);
- Contains no added substances, other than water and caramel colouring; and
- Contains a minimum alcoholic strength of 40% ABV (US 80 Proof).
As one can see, there are fairly stringent guidelines for a marketed drink to qualify as Scotch whisky. However, the production of a great Scotch goes far beyond these guidelines. Single Malt Scotches will use other grain cereals sparingly. The type of malting, distillation process, the choice to filter or not, specifics of ageing… all play a significant role in the finished product. That’s how you get the range from smoky, peaty, heavy scotches to the brighter ones with fruity, grassy aftertastes.
The Raw Ingredients
The raw ingredients are simple – Single Malt Scotch uses all-natural ingredients. The main ones used are malted barley, fresh spring water (preferably) and yeast.
The Use of Malted Barley
Scotch manufactures go to great lengths to select the right barley for malting, and then choosing the right “method”. There are some 5,500 different strains, ranked in categories 1-9. Only the top 3 categories are considered suitable. An additional consideration is whether the barley produces enough alcohol to be considered economically profitable. The varieties used to manufacture Scotch whisky today, in order of popularity, are Belgravia, Concerto, Propino, Quench and Shuffle. Some newer varieties, such as Moonshine, are more popularly used in Bourbon and other whiskies.
There is a general belief that fresh spring water from specific regions in Scotland (e.g. the Scottish Highlands) have mineral qualities that impart certain indelible tastes to Scotch Whisky. While this may be true, it’s equally the case that with the demand of Scotch growing over the globe, many distillers may be using whatever water source they can find, as long as it meets certain purity standards.
Malting, Mashing and Fermentation
The first step in the whisky-making process is the choice of barley as mentioned above. Once the barleys are brought in, they are “malted” by steeping the barley in water and spreading them across a malting floor, allowing the barley to germinate. The barley literally sprouts, thinking it is time to burst into plant form – causing the starch inside the barley to turn into sugars. Master distillers differentiate their products through a number of tweaks to this simple process, by choosing a specific type of barley, deciding whether it’s spread in two or six rows, the length of time it is allowed to germinate, etc. Other touches are often added. For example, the barley could be dried over peat, imparting a smoky flavour.
Once dried, the malt is ground into a coarse flour called “grist”, then mixed with hot spring water in a large vessel called the “mash tun”. The sugars from the malt dissolve in the tun, producing a sweet “wort”.
The wort is passed into a large container called a “washback”, where yeast is added to the mix, starting the process of fermentation. At this stage, the organic materials and carbohydrates decompose, producing ethanol (C2H5OH) along with by-products such as methanol (CH3OH), a number of congeners and carbon dioxide. This “wash” is then distilled.
The video below on the making of Glenfiddich illustrates some of the points quite nicely.
As mentioned above, distillation is a very old process – described in cuneiform tablets from Ancient Mesopotamia 4000 years back, then on through India, Egypt, Greece, Rome, Arabia … so on and so forth. Modern distillation has gone through a number of evolutions but has proved to be a remarkably durable and stable process in terms of the methods used, type of stills and materials chosen to make stills.
Types of Stills Used
Traditionally, copper has been used to make stills. Also, till the mid 19th century, pot stills (with their distinctive teapot or kettle shape) were considered to be de rigueur. However, other materials, such as steel or aluminium, began to make an appearance in the past 100+ years, especially after the emergence of the Continuous Steel invention by Agnus Coffey in the mid 19th century.
While the Continuous Stills produce cheaper stock, Scotch whisky continues to be produced using pot stills – traditional, costly but critical for quality control according to most Scotch distillers. Similarly, while cheaper and “sterile” materials such as stainless steel have been considered and partially adopted in certain types of whisky distillations (for example, Bourbons), copper remains the material of choice for Single Malt Scotch.
The decision to keep using copper stills, a costlier proposition, was triggered by the discovery of an added benefit of copper – it removes highly volatile sulfurous compounds – such as dimethyl trisulphide (DMTS) and the toxic ethyl carbonate – formed during the distillation process. In addition, copper absorbs yeast cells and certain microbes formed during fermentation and helps in the formation of esters, lending a fruity character to the final product. These last effects are noticed over and over during the distillation process – which by the way is one of the reasons why copper pot stills seem to work best. The more area that the distillates are exposed to copper, the more they react, and the end product seems to get tastier and more aromatic.
The Process of Distillation
Distilled spirits are produced from the wash that has been formed at the end of the malting, milling and fermentation process. As described above, the fermented ethanol is “polluted” with a number of carbon dioxide and congeners – some of which range from noxious to toxic. Distillation is a process whereby these “bad” compounds are being taken out while retaining the good ones.
To begin the distillation, the “wash” of fermented grains and water are fed into the bottom of an evenly heated pot. This will release evaporated particulates that can be condensed against a cool surface, led along a pipe and collected in a different container. This first distillate, often called “low wine”, can be distilled further to increase the concentration of ethanol and decrease “impurities”.
The first distillate, when it comes out, is relatively high in noxious odours and harmful impurities, which is why Scotch whisky, by law, is at least twice distilled. Harmful congeners can be responsible for heartburn, hangovers or serious health conditions. The two most harmful consigners – methanol and acetaldehyde – produce toxic side-effects. Other congeners, such as furfural and fusel oil, are less harmful and may even add a bit to the flavour and aroma of the finished product.
One of the main things to note is that along with the bad, there are also a host of “good” congeners, esters being a class of them. These add desirable attributes, including the flavours, aromas and tastes that we can sense when we sip a Single Malt Scotch, such as the scents of wood, smoke, grass, cinnamon and citrus fruits. The process of distillation is all about cleaning up harmful congeners while keeping the good ones.
The basic philosophy is simple – different compounds in the “wash” boil at different temperatures. Ethanol itself boils at 173.10F, a temperature lower than water’s boiling point.
Making “Head” and “Tail” out of It – The Foreshot, Feint and Middle Cut
As the wash is heated in the Pot Still, it evaporates. The evaporated liquid, which condenses and is deposited in an adjoining Spirit Still, should be rich in compounds that are produced at the right temperature.
Distillers will reject (a) the “Foreshot” or “Head” liquid produced at the very beginning in the lower ranges of temperatures, and (b) the “Feint” or “Tail” liquid produced at the end (in the upper range). Choosing the right “cut” is a skill honed with practise by master distillers.
As explained above, this process of choosing the right cut is made possible due to differentiated boiling points of the various compounds in comparison to the 173.10F boiling point of ethanol.
In particular, methanol, acetone and ethylacetate are removed at boiling points lower than ethanol (e.g., methanol evaporates at 148.50F). These compounds dominate the foreshot, while the certain long-chain alcohols produced at upper ranges of temperatures dominate the feint.
The central “cut”, which contains mainly ethanol and water, but also retains aroma and taste producing compounds that had been produced during fermentation, is the desired output.
The first distillate (“weak feint”) produces a relatively weak ethanol content, typically around 8% alcohol by volume (ABV), which is known by “low wine”. Besides the low ABV, there are still substantial trace elements of various congeners that are harmful to humans and contain noxious odours/tastes.
A second round of distillation will get rid of harmful impurities. This is one of the reasons why Scotch whisky must be at least double distilled, by law. The second distillation produces what is called “strong feint”, which produces 20%+ ABV in the output.
Double or Triple Distillation
There is some (though not much) debate on whether Single Malt Scotch should be double or triple distilled. While Irish whisky is traditionally triple distilled, Scotch is typically double distilled.
If a third round of distillation is employed, there are two ways to go about it. In some cases, there is an arrangement of three stills – with the third still being employed as the final Spirit Still. In other cases, the second still itself is used to re-distill one more time. In each case, the method if the same. There is a continuous process of feeding in the foreshots from the top and the feints from the bottom into the second still to continue re-purifying the contents while drawing as much ABV into the final mixture as possible.
We saw how triple distillation can be used to strengthen alcohol content and reduce impurities through the extra round of distillation. On the other end of the spectrum, though, successive distillations will rob some of the smoky, peaty and heavier flavours and mouthfeel that whisky drinkers often crave. For this reason, Single Malt Scotch whisky distillers tend to be purists – to them, the heavier, oily and spicy flavours are important, more so than the fruity accentuations which grow with progressive distillation steps. Also, the conventional wisdom is that some congeners such as furfural and fusel oil actually add to the aroma, taste and mouthfeel.
Using Worm Tubs or Shell-and-Tube Apparatus
In addition to the cool surfaces on the insides of the still, there are two types of apparatus that are used to condense the distilled spirit vapour – shell-and-tube or worm tubs. This is a vital step in producing malt whiskey, the choice of apparatus is dictated by the taste being sought.
Worm tubs involve copper coils submerged in cooling water tubs. However, the copper does not have prolonged exposure to the condensing spirit – so the end product ends up being more sulphury with meaty or vegetal notes.
The shell-and-tube construction involves copper even more directly since the copper comes in continuous, direct contact with the condensing spirit. This ends up producing a lighter flavour with fruity, grassy overtones when the whisky eventually matures.
Another debate that arises is whether Scotch whisky should be chill-filtered. Running the distilled product through paper, sand, and other filtration devices are sometimes thought to produce a “smoother” taste, and distillers such as Macallan do adopt this method. However, traditionalists feel that there is a loss of flavour and mouthfeel, so filtration is not always carried out. Filtered Scotch will state so on its label.
The final step to Scotch may be one of its most important ones, namely ageing. Unlike Bourbon and many other liquors that can be marketed after three months in a new cask, Scotch must be aged for a minimum of three years by law. That is in fact a very low boundary, most major distillers will age Scotch for a minimum of 10 years. Good Single Malt Scotch whisky is typically brewed between 12-21 years.
Choice of Barrels
The first matter to consider is the choice of barrels. Scotch is never brewed in new casks, but in bourbon or wine (often, sherry) casks. Casks are made of oak wood, from either American or European Oak Trees. The new casks are toasted or charred before use, which breaks up the cellulose in the wood carmelizes and wood sugars. Also, the Lignin is converted into Vanillin – the primary content of the extract of the vanilla bean. The cask is now alive.
What Happens during Ageing
Sherry or bourbon is aged in the cask for 2-3 years, during which time the young oak wood imparts significant flavour to the new distillate of whisky or wine. There is a difference, of course – the average sherry is 17.5% alcohol by volume (ABV) while the average bourbon can be up to 62.5% ABV. This means that sherry casks survive with more “life” for the next phase of their life.
Whisky distillers will buy the “aged” casks once the sherry or bourbon are taken out. Their first task is to “rejuvenate” the wood – scraping the inside surface and charring once again. From this point forward, the length of time (decades) that a cask lasts is dependent on how hard it has been used prior to reaching the Scotch distiller – by definition, a sherry cask can be used for at least one more “fill” than bourbon casks, which means that they last a decade or longer.
In the first years after the new whisky is added to a first-fill cask (the bourbon or sherry years of ageing are not really counted in the Scotch ageing lexicon), there is additive maturation – which means that the cask flavours impose themselves on the distillate. There is a general woodsy tone, but the overtones are vanilla (remember the Vanillin that had been activated by “toasting”), caramel (toffee) and oak. How much flavour is added depends on how old the cask being used is – in other words, whether it’s a 1st, 2nd or 3rd fill cask.
As the Scotch continues to age in the wooden cask, a second, more interactive, process begins. The whisky has its own distinct flavours coming out of a specific distillery, based on a number of factors that Master Brewers perfect – mainly special distillation techniques and the malt used – in order to distinguish their brand. Over time, it’s not only the cask that imparts flavour to the whiskey, but the distillery character blends in with the wood flavours and the two in a certain sense either compete or blend together nicely. Since the only reduction to distillery character over the years is likely to be a decrease in the peat smoke flavour, it remains strong many years later while the wood flavour is in a certain sense “used up”. And this is where the difference between a 1st fill and a 2nd fill whisky may come in.
The above effects do differ based not only on the age of the cask, but whether bourbon or sherry casks are used. In general, bourbon casks retain more vanilla, woody and peaty flavours while sherry casks tend to impart more fruity, citrusy or grassy flavours.
Scotch manufacturers may sometimes resort to “finishing” – the whisky is first aged in American Oak casks for 8 to 10 years till it “matures” and loses its overly unpleasant tastes. They are then transferred to 1st fill European Oak casks for 2-4 years. The end product is a 10-12 old single malt Scotch whisky with the cask and distillery flavours perfectly blended.
Bottling and Selling
The image above shows the bottling plant at the Glenfiddich distillery.
Once the casks are tapped and the whisky comes out, most distillers will add caramel colouring to produce the burnt amber colour we are familiar with. Most people don’t know this, but even after decades of ageing, the colour of malt whisky rarely gets much darker than golden yellow.
Bottled Scotch whisky must mention pertinent details, including the years it has been aged, and whether it has been triple-distilled or chill-filtered.
In Conclusion …
The process outlined above is tweaked in subtle and not-so-subtle ways by master distillers to produce the exact right combination of colour, texture, flavour, aroma and mouthfeel that will please your palate. As you take your next sip, or simply savour the aroma as the liquid swirls around your glass, take a second to appreciate what has been done for over a decade to make the experience perfect for you. Cheers!