How to make whisky
On a recent trip to Scotland with a couple of friends I visited a few whisky distilleries. The guided tours were quite fun, and usually finished with a tasting in a stylish, cozy room with plenty of special bottles on display. The tour guides were happy to answer any questions on the whisky production process, allowing us to soak in all that in-depth information.
While sipping on a glass (or dram) of whisky, it is common to talk about its viscosity, aromas, flavours, and other emotions associated with profound sensory experiences. Fun!
How does all this relate to the actual single malt scotch production process? I wanted to find out.
TLDR: Grind some barley, put it in water, let yeast turn it into alcohol, evaporate it, cool it down and save it in a wooden barrel for a long time.
Barley, water and yeast
Single malt scotch by definition is made of three things only: Barley, water and yeast. Barley grows on big fields and is usually imported from farmers in the nearby area. It is an important cereal grain that forms the basis for what a lot of people around the world get their nutrients from. Just like wheat, rye and oats.
Barley has two benefits over other grains:
- it is easier to grow
- it germinates faster
Malting
The first step is taking in a large amount of barley and adding water to it. The barley is immersed and dried multiple times, as if it was taking multiple baths. The moisture content goes up from 12% to around 45%, which breaks down the starch into sugar. Starch is like a chain of sugar molecules stuck together.
The barley only germinates every so slightly, until the tiny sprout reaches something like 75% of the grain size. This is because the sprout uses sugar to grow, and sugar is useful for making alcohol later on. So the germination is stopped at the right time by taking it out of the water. The remaining stuff is called green malt.
To fully stop germination, the barley needs to dry in large kilns. Moisture content goes down to about 5%. Traditionally this is done on a large floor with tiny holes in it. Below that is a giant heating source, with optional peat added to it to add smoky flavours.
Peat is basically a dense block of very old compressed old leaves and plants found in the ground. Peat on the Isle of Islay differs from mainland peat, because it includes different plants like seaweed. Orkney peat also has its own distinct aroma.
The (peat) smoke rises through the floor with tiny holes, drying and flavouring the green malt along the way.
Now we have malted barley.
Milling and mashing
The malted barley contains sugar, but also a lot of other stuff. To get the good parts, the barley has to be smashed into smaller parts first. The interesting thing is that this is usually done in old, heavy, big machines. They rarely brake down, so the company that made them went bankrupt because nobody needed new machines.
On top of that, there is practically just one guy in the UK that now knows how to service these old milling machines. He's probably making a killing.
The malted barley has to be milled to the exact right size, into something called grist. The next step is to add hot water to the grist, in which all those nice sugars will dissolve. If the grist is milled too fine, water won't pick up the sugar. If it is too coarse, water will run through too quickly.
Basically this works like your espresso machine: grind the beans to the right size, or water will flow through too quickly or not at all.
This process is called mashing and is done in a big round tank called a mash tun. A giant metal arm slowly moves through the tank to stir through something that looks like liquid porridge. Water is added a couple of times at different temperatures to make sure plenty of sugar is dissolved.
The bottom of this tank has tiny holes through which the water can escape, leaving the grain inside. This grain is usually fed to Scottish cattle, which is why their beef is allegedly pretty special.
Producing alcohol
Yeast is a special beast - a family of microorganisms that humans have been using for ages to bake bread and produce alcohol. There is a specific yeast species that converts sugar into CO2 and alcohol. They prefer 'peak' temperatures of 34C, anything higher than that and they are killed. The same holds for making sourdough bread, don't add hot water!
The sugary liquid wort is unloaded into big round wooden tanks called washbacks, where the yeast in liquid form is pumped also into. The yeast starts 'eating' away at the sugar, which produces alcohol and lots of CO2 bubbles. Sometimes this foamy layer overflows the tank, so they prepared the surrounding area to drain any excesses. The fermentation usually takes around 3 days.
The resulting liquid (wash) smells a bit like barbecued beer and holds around 7% alcohol. Several tour guides did mention though it is not so tasty, as the hop is still missing. But basically the process up until this point is similar to brewing beer.
For whisky we need something stronger than this. During the distillation process, the wash is heated in large copper stills until it evaporates. The vapour is rich with lots of alcohol and a few other molecules. This is because the alcohol vaporises at lower temperatures than plain water itself.
As the vapour rises, it is led through a copper tubing system with a few curves where it slowly cools down again. The actual shape of this system and the height of the stills influences which vapour molecules make it through, and which are left behind. This is just one factor that makes whiskeys across distilleries unique.
Vapour then condensates into liquid again. This time it is not barbecued beer, but a clear liquid called low wine, of around 25% alcohol.
The second distillation step generates a new liquid called the spirit, which is typically around 70% alcohol.
When the low wine is heated, a few molecules that we don't want typically evaporate first. The first part of the distillation process, known as the head, is taken out of the process because high concentrations of methanol and acetaldehyde are pretty bad for the human body.
This 'cutting' of the liquid is done in a glass box called the spirit safe. Someone knowledgeable goes there with modern tools (a thermometer and experienced nose) to measure exactly when the right time is to draw the line between good and bad.
Maturation
The resulting spirit has a very fruity flavour, but it may not be called whisky just yet. At this stage perhaps it could be sold as wodka or something similar. Most of the flavour is actually added by keeping the spirit in casks for many years. Tour guides typically say whisky flavour comes from around 60-80% from the type of casks used.
After the spirit has matured for at least 3 years in a cask, it may be called whisky. Interestingly there are a lot of distilleries that don't do their own maturation, as it requires a lot of space. Diageo, one of the biggest conglomerates, has a large warehousing area near Glasgow where brands like Talisker mature their whisky.
Simply put, there are two types of wood used for these casks:
- American white oak. Imported, they are usually old bourbon casks. Whiskies matured in these casks have a ligher colour.
- European oak. Usually old sherry, port, or sometimes wine or madeira casks. Usually this results in a dark coloured whisky.
In stores it is typical to find whiskies aged in multiples of 3 years: 9, 12, 15, or 18 years. As far as I know this has no reason other than tradition. The minimum of 3 years also means you can say something like, this whisky has matured 4 times the minimum age.
Other interesting facts
- High spirit stills usually mean more balanced, rounded flavours. Lower spirit stills allow for more different kind of flavours to make it to the top, possibly creating a more complex whisky.
- Stills are made of copper, which serves as a sort of filter for heavier molecules that are not so nice.
- When adding drops of water, sometimes a white cloud forms in whisky lower than 46% alcohol. Some bottles are filtered of this white cloud because it doesn't look nice. Look for bottles that are "non-chill filtered".
- The only artificial additive that may be added to single scotch is E150, also known as caramel colouring. Some distilleries use this to make the colour of the whisky darker. Look for "non-coloured" whisky.
- Whisky straight out of the cask has higher than 57% alcohol. Distilleries may dilute this up to 40% before bottling it. Look for "cask strength" whisky.