Q&A

How is whisky produced?

The production of whisky includes malting, grinding, fermentation, distillation, aging and other procedures. This article elaborates on the functions and effects of each step, as well as the differences in production techniques of various whiskies.

1. Raw Materials: Water and Barley

Water

Distilleries need plenty of clean low-temperature water for whisky brewing, so a stable water source is essential. Most distilleries use spring water, while others adopt lake water or municipal tap water. Different water sources have slight impacts on fermentation efficiency, yet most people believe water barely affects the final taste of whisky.

Barley

Distilleries prefer Scottish barley, though there is no legal obligation. Many distilleries use barley from other regions, and it is widely acknowledged that barley origin has little influence on flavour.

2. Malting

A barley grain is rich in starch. Malting creates suitable conditions to trigger barley germination. Barley is soaked in water and kept in a humid environment to sprout. Activated enzymes convert starch inside barley into sugar, which is the key substance needed for brewing. Once sufficient sugar is produced, germination is halted and the barley is dried immediately.

3. Drying Malt

  1. Hot air drying: This method does not alter the original flavour of barley.
  2. Peat-fired drying: Peat is a kind of semi-carbonized plant. It produces dense smoke containing phenolic substances when burning. These substances adhere to malt and endow whisky with a unique smoky flavour. Peat is easily accessible in island distilling regions, so this method is widely used and forms the typical feature of island-style whisky.

4. Milling

Dried malt is ground into coarse particles before saccharification. Strict control over temperature and duration during milling is vital. Excessively high temperature or prolonged grinding will degrade the quality of the final spirit.

5. Saccharification

Ground malt powder is put into a mash tun and mixed with hot water at 63.5°C. Starch is converted into sugar to form wort. The liquid is drained through porous equipment, and the process is repeated twice to extract sugar fully. Residual liquid is reserved for later saccharification.

  1. Slow draining yields clear wort and makes whisky with mild grain notes.
  2. Fast draining brings fine solid residues, creating whisky with rich flavours of dried fruits and nuts.

6. Fermentation

After cooling, wort is pumped into fermentation vats made of wood or stainless steel. Yeast is added to start fermentation, and the same type of yeast is used for all Scotch whiskies.

  1. Short fermentation (within 48 hours): Yeast converts sugar into alcohol rapidly, producing whisky with prominent malt character.
  2. Long fermentation (over 55 hours): More lipids are generated, resulting in lighter, more complex whisky with distinct fruity notes.

7. Distillation

Fermented wash is ready for distillation. Copper stills are adopted, and copper plays a decisive role in shaping whisky flavour. Brewers adjust the contact time between alcohol vapour and copper to achieve desired styles.

The alcohol content of fermented wash is about 8%. It is generally distilled twice in copper stills; some distilleries use triple distillation or special 2.81-time distillation. The first distillation raises the alcohol degree to around 23%, known as low wine. In the second distillation, the spirit is divided into heads, hearts and tails. Only the finest heart fraction is reserved for cask aging, while heads and tails are blended with new low wine for re-distillation.

Precise control over distillation details including copper contact, condensation and fractionation is essential, and each distillery formulates its own techniques accordingly.

Copper Contact

  1. Longer copper contact results in lighter and softer flavours. Larger stills tend to produce milder spirits than smaller ones.
  2. Shorter copper contact brings richer and more intense flavours.

Condensation

Alcohol vapour turns into liquid after condensation, and different condensation methods change whisky flavour greatly.

  1. Shell-and-tube condensation: Equipped with numerous cold copper pipes, it provides large copper contact area and softens the spirit taste.
  2. Worm tub condensation: A traditional method using coiled copper tubes soaked in cold water. With less copper contact, it makes full-bodied and robust whisky.

Fractionation

Distillate is separated into heads, hearts and tails. The cutting point directly affects flavour profile.

  1. Early cutting obtains delicate, fresh and elegant aromas.
  2. Late cutting gains richer, oilier and fuller flavours with obvious smoky tones.

8. Cask Aging

Newly distilled spirit is filled into oak casks for maturation. The casks were previously used to age sherry, bourbon, wine or are brand-new oak casks. Oak casks reduce harshness of raw spirit and infuse diverse wood flavours. The fusion of flavours greatly enriches the complexity of whisky. Aging duration, cask age and cask type all exert huge influences on whisky quality.

9. Bottling

After aging is completed, whisky is prepared for bottling with three optional processes:

  1. Chill-filtering: It makes whisky clearer but sacrifices part of its original taste and aroma.
  2. Colour adjustment: Adding caramel colour unifies and stabilizes liquor hue.
  3. Alcohol adjustment: Scotch law stipulates that the minimum alcohol content of bottled whisky is 40%. Cask-strength whisky has gained growing popularity nowadays.