Distillation is used to increase the alcohol content and to remove undesired impurities such as methanol.
There are two types of stills in use for the distillation: the pot still (for single malts) and the Coffey still (for grain whisky). All Scotch malt whisky distilleries distill their product twice except for the Auchentoshan distillery, which retains the Lowlands tradition of triple distillation. Springbank Distillery in Campbeltown is unique in that it distills two and a half times. This is achieved by distilling half the low wine (1st distillation) for a second time, adding the two halves together and then distilling the complete volume a final time.
For malt whisky the wash is transferred into a wash still. The liquid is heated to the boiling point of alcohol, which is lower than the boiling point of water. The alcohol evaporates and travels to the top of the still, through the “lyne arm” and into a condenser—where it is cooled and reverts to liquid. This liquid has an alcohol content of about 20% and is called “low wine”.
The low wine is distilled a second time, in a spirit still, and the distillation is divided into three “cuts”. The first liquid or cut of the distillation is called “foreshots” and is generally quite toxic due to the presence of the low boiling point alcohol methanol. These are generally saved for further distillation. It is the “middle cut” that the stillman is looking for, which will be placed in casks for maturation. At this stage it is called “new make”. Its alcohol content can be anywhere from 60%–75%. The third cut is called the “feints” and is generally quite weak. These are also saved for further distillation.
Grain whiskies are distilled in a column still, which requires a single distillation to achieve the desired alcohol content. Grain whisky is produced by a continuous fractional distillation process, unlike the simple distillation based batch process used for malt whisky. It is therefore more efficient to operate and the resulting whisky is less expensive.