Wait Reek isn’t just a character in Game of Thrones?

For centuries, peat has been the secret ingredient behind some of the world’s most distinctive whiskies. Found in abundance across Scotland’s windswept landscapes, peat is an organic material formed over thousands of years from decomposed plant matter in waterlogged conditions.

When dried and burned, it produces a thick, aromatic smoke known as reek, which infuses whisky with its signature smoky, earthy character. Peat actually burns quite cold, it’s said when its burning at peak smokiness it is cool enough to pick up by hand.

Peat smoke plays a crucial role in the malting stage of whisky production.

After barley grains are soaked to begin the germination process, they are dried in a kiln to halt further growth. In peated whisky production, as is common in the island whiskies of Scotland. The drying process is carried out over a peat-fuelled fire, allowing the reek to penetrate the grain.

The intensity of the smoky flavour depends on how long the barley is exposed to the reek and the level of phenols—the chemical compounds responsible for those distinctive smoky, medicinal, and maritime notes.

There is a slight caveat. The barley can only be exposed to the smoke for about 18 hours, known as the break point. At this time it dries out and cannot absorb more smoky flavour.

These phenolic parts per million (PPM) determine just how smoky a whisky will be, with lighter peated whiskies sitting around 10-20 PPM and heavily peated drams, such as those from Islay’s Laphroaig or Ardbeg, exceeding 50 PPM. The smokiest whisky ever produced is Octomore by Bruichladdich, which can reach over 200 PPM—an absolute peat monster. Not to be confused with Swamp Monster the independent bottling.

Not all peat is the same, and its influence on whisky is determined by both where it is sourced and how it is cut. Peat found in different regions of Scotland has varying compositions, with some being rich in heather and moss, producing a gentler, earthier smoke, while others, such as the carbon-rich peat used by Ardmore, impart a dense, sooty quality.

The depth of the peat cut also plays a role—shallower cuts contain more plant matter and burn with a sweeter smoke, whereas deeper cuts produce a more intense, tarry aroma.