Peat and Terroir: Why Islay Tastes Different from the Highlands
Peat is partially decayed vegetation, compressed into a wet, dense material that can be cut, dried, and burned. In whisky production, peat smoke is applied to malted barley during the malt-drying stage, depositing phenolic compounds onto the surface of the grain — phenols that survive fermentation and distillation to flavour the eventual whisky. But not all peat is the same. The composition of peat — the plant species that decayed into it, over what time, in what climate — produces dramatically different smoke characters.
Islay peat
Islay peat is the most famous: dense, coastal, formed largely from sphagnum moss, heather, and sea-influenced vegetation over thousands of years. The phenol profile is heavy on the medicinal end — iodine, TCP, hospital-corridor notes — combined with marine character. Different Islay distilleries cut peat from slightly different bogs, with measurable differences in profile.
Orkney peat
Orkney peat is composed of more heather, less sphagnum than Islay, and almost no coastal influence (Orkney peat bogs are inland, surprisingly far from the sea). The smoke is lighter, more aromatic, with floral and honeyed notes layered onto a less intense base phenol level. Highland Park is the canonical Orkney peat expression.
Highland mainland peat
Highland mainland peat (used historically at distilleries like Ardmore and Glen Garioch, currently at Tomintoul/Old Ballantruan and a few others) is more forest-influenced — pine needles, heather, lichen. Profile tends toward smokier-than-medicinal with a wood-fire character.
Off-Scotland peats
Irish peat (used at Connemara, the principal Irish peated single malt) has its own character. Mainland European peats (the few European craft distilleries that have experimented with peat) and Tasmanian peat (used at distilleries like Lark) are starting to define their own regional characters as the global peated category expands.
How peat is measured
The standard measure of peat intensity in whisky is "ppm" (parts per million) of phenol in the malted barley before fermentation. Standard non-peated malt is 0-1 ppm; lightly peated (Highland Park) around 20 ppm; heavily peated Islay (Lagavulin, Laphroaig) around 35-40 ppm; very heavily peated (Ardbeg) around 55 ppm; the extreme (Bruichladdich's Octomore) regularly exceeds 100 ppm and has gone as high as 309 ppm.
What survives distillation
Distillation strips out some phenols, fermentation has its effects, and the final whisky's phenol count is significantly lower than the malt ppm — typically about a third to half survives. A 50 ppm malt becomes a 20 ppm finished whisky.
From reading to planning
The peated-whisky geography centres on Islay (and the southern Inner Hebrides), with secondary centres at Orkney (Highland Park, Scapa lightly), the mainland (Ardmore, BenRiach's Curiositas range, others), Skye (Talisker), and increasingly Japan (Yoichi peated, Hakushu lightly peated). The interactive map shows the geography.