How is malt whisky made?

Updated: Nov 16, 2019


Malt Whisky is enjoyed across the globe. However, not many of us have a good understanding of what exactly malt whisky is and how it is made. This article will break down the malt whisky making process in an easy to understand manner for the whisky beginner and experienced drinker alike.



To begin with, malt whisky has only 3 ingredients - Barley, Water and Yeast


The steps in the production of malt whisky are


Step 1 : Malting - Conversion of barley grain to 'Malt'

Step 2 : Milling - Grinding down malt to 'Grist'

Step 3 : Mashing - Conversion of the grist to a sugary liquid called 'Wort'

Step 4 : Fermentation - Conversion of the wort to a low ABV beer called 'Wash'

Step 5 : Distillation - Concentration of the wash to a high ABV spirit called 'New Make'

Step 6 : Maturation - Aging of the new make to produce 'Whisky'


Let us look at these steps in detail


Step 1: Malting

Malting of barley is done in order to get access to its starch and for the development of natural enzymes. These enzymes are critical as they convert the starch into soluble sugars which will then be fermented to create alcohol. In order to for this to happen the barley grain must be 'tricked' into thinking that it is time to germinate.


The barley goes through a process of steeping in water and drying multiple times to activate growth. Once the steeping is done, it is time for the barley to germinate. Historically, the barley would be spread on a malting floor and turned periodically to dissipate carbon dioxide and keep the rootlets from tangling. The maltster continuously checks the grain until the starch has sufficiently been exposed. Once this is done, the germination must be stopped, lest the plant grows and consumes all the starch.


Floor malting which used to be the industry standard, has become rare in Scotland, with only 8 distilleries still doing it. Out of these 8, only Springbank floor malts all its barley while the other distilleries source most of their barley from commercial malting companies. These commercial maltsters use large scale industrial equipment to produce larger volumes.


Kilning is the process by which the germination is stopped by heating the germinated grain. Traditionally, this was done by placing the barley on a large mesh-like floor, under which would be a fire to send heat up through the mesh and into the barley. The smoke would then escape through the pagoda shaped chimney that is common in most distilleries in Scotland.


This stage is of particular interest for those of you who love your peaty whisky! In Scotland, and more so in the islands like Islay there aren't many trees. The most widely used heat source, therefore was peat. Peat is essentially partially carbonised vegetation which is abundant in the Scottish highlands. This fuel, which was used in households, was logically also used to dry the barley. The smoke from this peat is absorbed by the barley grain and lasts right through to the new make and aged whisky. Some examples would be Laphroaig, Ardbeg, Ardmore, Highland Park and so on. Even some famously unpeated whiskies have peated expressions like the Glenlivet Nadurra and Balvenie Peat Week, just to name a couple.


Once the kilning is done and the germination has been stopped, the grain has now become malt and is ready for the next process - Milling.



Step 2: MILLING

Milling of malted barley is essentially the process of grinding it down to get it ready for the mashing process. While this might sound like a simple process, it is critical to get the consistency of the ground barley called Grist, exactly right.


The barley is first put through a de-stoner to remove any stones or other unwanted particles. There are different types of mills, but the most commonly used in Scotland are roller mills from Porteus and to a much smaller extent from Robert Boby.


The Porteus mill is a combination of two heavy rollers rotating in unison. The first roller breaks the husk and the second grinds down the barley to the desired consistency. Typically distillers like a ratio of 20% Husk, 70% Middles and 10% Flour. Most distilleries in Scotland still use Porteus Mills that date back to the early 1900s. What is interesting here is that the mills were so good, that they never broke down and this led to the company going out of business!


Since the mashing process requires water to pass through the grist and extract the sugar, the ratio mentioned before is very important. If there is too much husk, the water would just flow through thereby not extracting sugars as desired.



The grist is now moved onto Step 3 - Mashing.


Step 3: MASHING

Mashing is the process of converting starch in the grist to fermentable sugars by passing hot water through it. This is done in what is called a mash tun.


The grist is fed into the mash tun which is a large vat with rotating arms. Typically, there are 3 waters added to the grist, now called the mash. The first water is generally around 65C, second is 75C and third is 85C. Some distilleries run through a fourth water as well. As the water passes through the grist it breaks down the starch into soluble sugars and the sugar water is drained through small perforations at the bottom of the mash tun.


Traditionally mashing was done in a Rake & Plough mash tun, while the modern mashing is done in Lauter tuns. The difference is that in the lauter tun, the bed of grain is not disturbed, thereby forming a natural filter for the wort to drain through the perforations on the floor.


At the end of the mashing, the spent grain leftover in the mash tun is called Draff and is high in protein. This is either sold on as cattle feed or used as fuel for bio-gas plants in some distilleries.


The sugar rich water from the first two waters is called the Wort. The third and fourth waters, called the sparge are reused for the next mashing cycle.


Before the Wort is passed onto the next step i.e. Fermentation, it passes through a heat exchanger to drop the temperature to below 30C, to ensure that the yeast used for fermentation would die. The intermediate vessel used to hold the wort coming out of the Mash Tun is called the Underback.



STEP 4 : Fermentation


Fermentation is the process where yeast acts on the sugars in the Wort to produce alcohol and carbon dioxide.


The cooled wort is pumped into fermenters, called Washbacks. Traditionally washbacks were made of wood, while most modern washbacks are made of stainless steel.


Wooden washbacks are typically made from Douglas Fir or Oregon Pine. These woods are preferred since they have tight grains, no knots and produce long planks. This is very important as washbacks need to be leak proof and tall to hold large quantities of wort. A notable exception is Chichibu distillery in Japan that uses Mizunara (Japanese Oak) which is notoriously leak prone and hard to work with.


Advocates of wooden washbacks would argue that these are better as they provide a more flavourful wash. This is attributed to bacteria that is retained in the washback even after it is cleaned. Those who prefer stainless steel washbacks argue in terms of efficiency and cleanliness.


Distillers Yeast that is used for fermentation may be of different strains, but they all originate from one - Saccharomyces cerevisiae. They Yeast may be in liquid, semi-dry or dry form.


The Yeast is 'pitched' into the wort. The yeast immediately starts converting the sugar in the wort to alcohol and CO2. This process typically lasts 2-3 days. The conversion of all sugars to alcohol takes approximately 48 hours. Letting the wash remains in the washbacks longer results in a more complex wash as at this point more compounds like fruity esters, fatty alcohols and aldehydes are formed.


A large amount of the whisky's, especially sweet fruity flavours are developed at this stage. The end product is a ~5-8% ABV liquid, similar to beer called Wash which is then passed onto the next step - Distillation.



Switcher blades cutting bubbles in the Mizunara washbacks at Chichibu Distillery, Japan, to prevent the wash from overflowing.

Extremely vigorous fermentation at Bardstown Bourbon Company. While this is not a wash of malted barley, there can be an equal amount of in malt wash fermentation. All the energy you see is generated by the yeast and there is no external heat provided in any way.


STEP 5: DISTILLATION


Distillation is the process by which the alcohol in the Wash is conventrated to arrive at a high ABV New Make.


Most Scotch Malt Whisky is double distilled in copper pot stills. In a nutshell, the wash is heated in a pot to separate out the alcohol at its low boiling point of 78.37°C from water which as well know, boils at 100°C. When the vapours rise, they are passed through a condenser which has cool water running on the outer jacket, to cool down the vapour, converting it back into liquid.


In the first distillation, often referred to as the stripping run, the alcohol is separated to an extent from the rest of the water and all the solid elements from the wash. The product of this distillation is the Low Wines, generally around 20-30% ABV. This distillation is done in the Wash Still.


In the second distillation, the low wines are heated up in the Spirit Still and four components are removed - The Heads/Foreshots, Hearts/Middle and Tails/Feints. The Heads have toxic chemicals like Acetone and Methanol with boiling points lower than the desired Ethanol. The Tails have heavy compounds that can make you sick like Fusel Oils and Butyl Alcohol, which are heavier than Ethanol. It is the Hearts or Middle Cut that is rich in Ethanol which is desirable and is now called the New Make. The New Make is typically 63.5% to 75% ABV. Distillers can choose to distill higher, but cannot go above 94.8% if they want to use it for whisky. How the Heart Cut is chosen greatly determines the character of the whisky as there as some desirable flavours that can be drawn both from the Heads and the Tails. This is where the skill of the distiller comes to the fore.


The Heads and Tails are put back in the Spirit Still for the next batch of the Spirit Still run.


The reason that copper is used for stills is that it removes sulphur and other undesirable compounds during the distillation process. It also heats evenly to ensure efficient distilling.


The shape of the still greatly influences the character of the whisky. In general, the more reflux there is, the lighter the new make will be. Reflux is when the vapours do not make it to the condenser, but instead condense back into the still. The more reflux, the more distillation and hence the more refined spirit. One factor is the heigh of the still. Another is the angle of the arm at the top of the still that leads to the condenser called the Lyne arm. If the arm is going upward, the spirit needs to work harder and there is higher likelihood of reflux.


Heavier spirit : Short still, Fast Distillation, Lyne Arm Going Down, No Bulb or equivalent shape

Lighter Spirit : Tall Still, Slow Distillation, Lyne Arm Going Up, Bulb or equivalent shape


There are two types of condensers as well - Shell and Tube which has more copper contact, yielding a lighter spirit and Worm Tubs which have lower copper contact, yielding a heavier spirit.


Most distilleries heat the still using a steam jacket. Traditionally however, most distilleries heated directly using a fire source. This lead to a number of inefficiences, but some distilleries still do this as they feel it is a factor in the character of their whisky.


In Scotland, the two triple distilled whiskies are Auchentoshan and Hazelburn. Recently Benromach released a triple distilled expression as well.


Most Scotch distilleries 'cut' the new make down to around 63.5% ABV before the next step - Maturation.



STEP 6: MATURATION


In Maturation, clear new make is put into wooden casks and left to age and become whisky. Scotch whisky must be matured for at least 3 years only in oak casks. It is estimated that over 60% of the flavour of whisky comes from the wood.


Casks come in various sizes from the 40 litre firkin up to the 1000 litre Tun. The most commonly used is the 200 litre Bourbon barrel.


When casks are made, the inside is exposed to direct fire for toasting and/or charring. Toasting caramelises the wood releasing compounds like Vanillin which gives many whiskies that distinctive vanilla flavour. Charring creates a level of charcoal that absorbs sulphur and other undesirable flavours.


As temperature changes, the whisky interacts with both the wood and the outside atmosphere. When temperature decreases, whisky gets squeezed into the wood and when it increases, the whisky comes out. Over years this interaction moulds the new make into whisky, as we know it.


Every year a percentage of whisky is lost to the outside atmosphere. This Angel's Share varies across regions : 1-2% in Scotland, >8% in tropical Asia etc. Some argue that this means that whisky matures faster in hotter conditions.


Most casks used to mature malt whisky are ex-bourbon barrels. The reason is that for a whiskey to be called bourbon it must be matured in a new charred oak cask. This makes a vast number of casks still in pristine condition available to other whisky makers who don’t have such restrictions. The other most common casks used previously held Spanish sherry. Each of these casks pass on different characteristics to the whisky. In recent


The most commonly used oaks to mature whisky are American and European. European tends to have the more robust rich spicy flavour due to its higher tannin content, while American tends to be more on the mellower vanilla and coconut profile. Casks are chosen according to the desired flavour profile. Over the past couple of decades a number of distilleries have chosen to 'finish' their whiskies in casks that have held a variety of different spirits and wines previously like Rum, Port wine, White wines, Red wines to even Sake and Tequila.



The casks are constantly monitored by the distillery team typically led by the Master Blender. The malt whisky could either be bottled as a Single Malt or blended with either other malt whiskies or grain whiskies or both. We'll discuss that in the next article.


Additionally, the Single Malt whisky could either be from a vatting of different casks or just just from a single cask. The whisky is most commonly 'cut' with water, before bottling both to make it drinkable by a wider audience as well as achieve a competitive price. However, cask strength bottlings are becoming increasingly popular with whisky enthusiasts preferring to do the watering down of the whisky, if needed, on their own.


This brings us to the end of this article, but by no means the end of the whisky education this blog hopes to impart. Keep following us on our whisk(e)y journey across the world.




Uday Balaji is the Managing Partner of The Whisky Advisor, your one stop shop for Whisk(e)y training, events, advisory and beyond. Uday is based out of India, but constantly travels across whisky regions learning and passing on knowledge about whiskies from across the world. Get in touch with him at uday[at]thewhiskyadvisor.[com] if you would like to collaborate.