Peat, Smoke and PPM
Peat is what gives Islay its smoke. Understanding how it works — and what the famous "PPM" number does and doesn't tell you — will change how you read a whisky label.
What peat is
Peat is partially decomposed plant matter — sphagnum moss, heather, grasses — that has built up in waterlogged bogs over thousands of years, growing only about a millimetre a year. Cut, dried and burned, it gives a thick, aromatic smoke. Peat from different places smells different: Islay's is maritime and mossy, Orkney's rich in heather.
How it gets into whisky
Peat smoke is used while kilning the germinated barley. Smoke compounds called phenols — guaiacol, cresols and others — cling to the damp malt. They survive mashing, fermentation and distillation to reach the spirit.
What PPM means
PPM (phenol parts per million) is measured on the malted barley, not the finished whisky. A good deal of that phenol content is lost in distillation and maturation, so a malt specified at 50 PPM does not give a whisky with 50 PPM of phenols. The spirit cut matters too: collecting later in the run captures more of the heavy phenols, so two distilleries using the same malt can differ in smokiness.
A rough scale
| Malt spec | Examples |
|---|---|
| Unpeated (under ~2 PPM) | Most of Speyside, Bunnahabhain core, Bruichladdich |
| Lightly peated (~10–20) | Highland Park, Talisker, Springbank |
| Medium (~20–30) | Bowmore |
| Heavily peated (~35–55) | Lagavulin, Caol Ila, Laphroaig, Kilchoman, Ardbeg |
| Super-heavily peated (80+) | Octomore — 08.3 reached 309 PPM, the peatiest yet |
See every distillery and bottling ranked on the Peat Index.
Smoke is not all the same
"Peaty" covers many aromas: bonfire and ash, tar and rope, iodine and seaweed (Laphroaig's "medicinal" note), smoked meat, sweet pipe tobacco. As peated whisky ages, smoke softens and fruit and sweetness rise — a 25-year-old Laphroaig is gentler than its 10.