Although whiskey is a complex spirit which contains many different flavours and aromas, the process for making it is simple. In fact, you might be surprised to discover that making whiskey only requires three basic ingredients – water, yeast, and grains.

However, the ways these three ingredients are processed, distilled, and aged can vary greatly. The type of whiskey being produced, the region where it is being produced, and the distillers’ personal approach to whiskey can all change how it is made.

To help you better understand what you are drinking, this post will explain how whiskey is made, all the way from water/yeast//grains to your glass.

Stage 1: Processing and Milling of Grains

Barley grain for milling

All whiskies are made from a mash of fermented grains. However, the type of grains used will vary based on the type of whiskey being produced. Some whiskies will only use a single grain, while others will contain several.

There are several rules which specify how much of each grain should be included to make a specific type of whisky. For example:

  • Single malt Scotch whisky is 100% malted barley
  • Bourbon has at least 51% corn
  • Rye whiskey has at least 51% rye
  • Wheat whiskey has at least 51% wheat
  • Single grain Irish whiskey is 100% of a single grain (corn, wheat, barley etc)

All whiskeys will include some malted grains (germinated grains). These grains have been soaked in water then left on a flat surface for about a week to germinate. They are then placed in a kiln to dry at low heat.

Having malted grains is essential for making whiskey as they contain an enzyme called amylase, which helps to convert the grain’s starches into sugars. This is very useful during the mashing stage.

Some whiskies can only contain malted grains, like Single Malt Scotch Whisky. It must contain 100% malted barley. Scotch whisky is also notable because it uses peat when drying malted barley. This gives the barley a very smokey flavour that is noticeable in the finished whisky.

Stage 2: Mashing

Erik Charlton from Menlo Park, USA [CC BY 2.0], via Wikimedia Commons

Next, the grains that are being used to make the whiskey will be ground up to create a ‘grist’. The grist is added to a large vat called a ‘mash tun’, which contains warm water. This mixture is agitated to extract sugars from the grains before the fermentation stage.

After the mash has been agitated for several hours, it is filtered so only a sugar-rich liquid remains. This liquid is called the ‘wort’ and will be used in the fermentation stage. The mash can be processed multiple times at different temperatures to obtain as much wort as possible.

Stage 3: Fermentation

Once the wort has cooled, it is placed into a large tank called a washback. Traditionally, these tanks were made of wood, but it is now common for distilleries to use stainless steel washbacks.

Yeast is added to the wort, which starts the fermentation process. The yeast will start eating the sugar and convert it into alcohol. It also produces ‘congeners’, which are molecules partially responsible for the flavours found in whiskey.

The type of yeast used can alter the flavour of the whiskey and it is common for distilleries to only use certain strains of yeast. Fermentation continues for at least 48 hours. At this point, the wash is relatively low in alcohol, with an ABV of between 5 to 10%.

Stage 4: Distillation

Copper stills at the Glenfiddich distillery

During distillation, the wash is heated so the alcohol (which boils at 78 degrees) is transformed into a vapour while the water (which boils at 100 degrees) does not. The alcohol vapour is cooled by a water-cooled condenser and transforms back into a liquid.

The temperature of the still will determine the proportion of water and alcohol that is collected. If the temperature is too high, the still will collect a higher proportion of water, as it transforms into a vapour at higher temps. If it is too low, the alcohol collected may be very pure and will have less flavour as it won’t contain any congeners.

It’s important to note that not all congeners are good as they can also impart bitter flavours. This is why the temperature must be closely monitored during distillation.

Distilleries will typically use two stills which are connected to one another. The first still will contain the wash and is used to produce a liquid called ‘low wines’. This liquid is about 20 per cent alcohol. This solution then flows into a second still called the ‘spirit still’ and is heated again to obtain a much stronger spirit.

The distiller won’t use all of the spirit produced by the spirit still. The first part of the distillation usually contains pungent congeners which are unpleasant to taste. The second part of the distillation contains valuable distillate suitable for whiskey production. The last part of the distillation is very weak and also contains unfavourable congeners which negatively impact the flavour of the whiskey.

The types of stills used will vary based upon the whiskey being made. Scotch whisky will use large copper pot stills, while Irish whiskey is often made using column stills. American whiskeys can use many different types of stills.

Most types of whisky will be distilled twice, however it’s common for Irish whiskey to be distilled three times. The liquid produced after distillation is called a ‘high wine’. It usually contains about 70% alcohol.

Tennessee whiskey is unique because it filters the high wine through charcoal after distillation. This is done to remove unsavoury congeners from the spirit.

Stage 5: Maturation

Barrels of whiskey on shelves

The distilled spirit is then placed into timber casks to age. Some whiskeys have specific rules about the types of timber used and how long the whiskey should be aged for. Scotch whisky, for example, must be aged in oak casks for a minimum of three years.  

Whiskey is most often aged in charred white oak barrels. In the United States, these barrels are brand new. However, it is common for Scotch and Irish whiskies to use barrels which have previously been used for other purposes in order to impart more flavour.

As the whiskey ages, the spirit (which contains water, alcohol, congeners) and the timber cask interact in various ways — not all of which are fully understood. The wooden cask will begin to impart its flavour into the whiskey. Some of the more unpleasant flavours in the whiskey will also dissipate.

The temperature, air quality, and humidity can all have an impact on this process, which is why the environment where barrels are stored is crucial.

Stage 6: Blending and Bottling

Many bottles of Jameson whiskey

Once the whiskey has aged a sufficient length of time, it is ready to be bottled. Some whiskeys are also blended, which involves two or more batches of whisky being combined to create a spirit with a more appealing flavour. It is now ready to enjoy!