Scotch whisky has a reputation for its smokiness. Whether just a hint in a blended whisky or a full-on bonfire malt, dry smokiness is synonymous with all things ‘Scotch’. Above all peat is synonymous with Islay, but not exclusively.
‘Peatiness’ is introduced to a whisky at the end of the malting process during kilning (drying) the grain. As a traditional quirk of the islands and some parts of the highlands during the early generations of malt whisky production, the most readily available fuel to fire the kiln was locally sourced peat, which is a type of moss that has developed over millions of years. If cut from the earth and dried, peat burns with a particularly distinctive thick smoke, which has a very dry, smoky aroma. Therefore, malted barley that has been kilned using peat retains an intensely dry smokiness, which transfers into the mash and later the spirit.
These smoky compounds are called phenols, and the level of ‘peatiness’ observed in grain is measured in phenol parts per million (ppm).
Some distilleries are traditionally very peaty, while others contain just a wisp of smoke. However surprisingly few distilleries today actually produce a smoky/peaty profile, and on top of this, just to confuse matters, any distillery has the capability to do a separate peated run. Balvenie, Ardmore, Tomintoul, Glendroach… they’re all at it!
By comparison, unpeated barley would traditionally be dried using coke, a type of coal with gases removed.
Interestingly, even if a single malt is made using barley malted to 35ppm, it doesn’t necessarily mean that the resulting spirit is 35ppm. In fact, much of the ppm is stripped out of the spirit during the distillation process, depending on copper contact and distillation process.